Glia a Promising Target for Neuropathic Pain – Ketamine Acting on Glia More Than on Neuronal NMDA Receptors?

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 Three important new articles from March, August and November 2011, show ketamine acts on glia.

Emphasis within articles is mine.

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Microglia: a promising target for treating neuropathic and postoperative pain, and morphine tolerance.

Abstract

Management of chronic pain, such as nerve-injury-induced neuropathic pain associated with diabetic neuropathy, viral infection, and cancer, is a real clinical challenge. Major surgeries, such as breast and thoracic surgery, leg amputation, and coronary artery bypass surgery, also lead to chronic pain in 10-50% of individuals after acute postoperative pain, partly due to surgery-induced nerve injury. Current treatments mainly focus on blocking neurotransmission in the pain pathway and have only resulted in limited success. Ironically, chronic opioid exposure might lead to paradoxical pain. Development of effective therapeutic strategies requires a better understanding of cellular mechanisms underlying the pathogenesis of neuropathic pain. Progress in pain research points to an important role of microglial cells in the development of chronic pain. Spinal cord microglia are strongly activated after nerve injury, surgical incision, and chronic opioid exposure. Increasing evidence suggests that, under all these conditions, the activated microglia not only exhibit increased expression of microglial markers CD 11 b and Iba 1, but also display elevated phosphorylation of p38 mitogen-activated protein kinase. Inhibition of spinal cord p38 has been shown to attenuate neuropathic and postoperative pain, as well as morphine-induced antinociceptive tolerance. Activation of p38 in spinal microglia results in increased synthesis and release of the neurotrophin brain-derived neurotrophic factor and the proinflammatory cytokines interleukin-1β, interleukin-6, and tumor necrosis factor-α. These microglia-released mediators can powerfully modulate spinal cord synaptic transmission, leading to increased excitability of dorsal horn neurons, that is, central sensitization, partly via suppressing inhibitory synaptic transmission. Here, we review studies that support the pronociceptive role of microglia in conditions of neuropathic and postoperative pain and opioid tolerance. We conclude that targeting microglial signaling might lead to more effective treatments for devastating chronic pain after diabetic neuropathy, viral infection, cancer, and major surgeries, partly via improving the analgesic efficacy of opioids.

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Ketamine depresses toll-like receptor 3 signaling in spinal microglia in a rat model of neuropathic pain.

Abstract

Reports suggest that microglia play a key role in spinal nerve ligation (SNL)-induced neuropathic pain, and toll-like receptor 3 (TLR3) has a substantial role in the activation of spinal microglia and the development of tactile allodynia after nerve injury. In addition, ketamine application could suppress microglial activation in vitro, and ketamine could inhibit proinflammatory gene expression possibly by suppressing TLR-mediated signal transduction. Therefore, the present study was designed to disclose whether intrathecal ketamine could suppress SNL-induced spinal microglial activation and exert some antiallodynic effects on neuropathic pain by suppressing TLR3 activation. Behavioral results showed that intrathecal ketamine attenuated SNL-induced mechanical allodynia, as well as spinal microglial activation, in a dose-dependent manner. Furthermore, Western blot analysis displayed that ketamine application downregulated SNL-induced phosphorylated-p38 (p-p38) expression, which was specifically expressed in spinal microglia but not in astrocytes or neurons. Besides, ketamine could reverse TLR3 agonist (polyinosine-polycytidylic acid)-induced mechanical allodynia and spinal microglia activation. It was concluded that intrathecal ketamine depresses TLR3-induced spinal microglial p-p38 mitogen-activated protein kinase pathway activation after SNL, probably contributing to the antiallodynic effect of ketamine on SNL-induced neuropathic pain.

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Microglial Ca(2+)-activated K(+) channels are possible molecular targets for the analgesic effects of S-ketamine on neuropathic pain.

Abstract

Ketamine is an important analgesia clinically used for both acute and chronic pain. The acute analgesic effects of ketamine are generally believed to be mediated by the inhibition of NMDA receptors in nociceptive neurons. However, the inhibition of neuronal NMDA receptors cannot fully account for its potent analgesic effects on chronic pain because there is a significant discrepancy between their potencies. The possible effect of ketamine on spinal microglia was first examined because hyperactivation of spinal microglia after nerve injury contributes to neuropathic pain. Optically pure S-ketamine preferentially suppressed the nerve injury-induced development of tactile allodynia and hyperactivation of spinal microglia. S-Ketamine also preferentially inhibited hyperactivation of cultured microglia after treatment with lipopolysaccharide, ATP, or lysophosphatidic acid. We next focused our attention on the Ca(2+)-activated K(+) (K(Ca)) currents in microglia, which are known to induce their hyperactivation and migration. S-Ketamine suppressed both nerve injury-induced large-conductance K(Ca) (BK) currents and 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS1619)-induced BK currents in spinal microglia. Furthermore, the intrathecal administration of charybdotoxin, a K(Ca) channel blocker, significantly inhibited the nerve injury-induced tactile allodynia, the expression of P2X(4) receptors, and the synthesis of brain-derived neurotrophic factor in spinal microglia. In contrast, NS1619-induced tactile allodynia was completely inhibited by S-ketamine. These observations strongly suggest that S-ketamine preferentially suppresses the nerve injury-induced hyperactivation and migration of spinal microglia through the blockade of BK channels. Therefore, the preferential inhibition of microglial BK channels in addition to neuronal NMDA receptors may account for the preferential and potent analgesic effects of S-ketamine on neuropathic pain.

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The material on this site is for informational purposes only,

The material on this site is for informational purposes only,

and is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider.


For My Home Page, click here: 

Welcome to my Weblog on Pain Management!

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Gliopathic Pain — when Neuropathic Pain Treatment Fails

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Coming soon, though these stand on their own:

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Modulation of microglia can attenuate neuropathic pain symptoms and enhance morphine effectiveness.

Abstract

Microglia play a crucial role in the maintenance of neuronal homeostasis in the central nervous system, and microglia production of immune factors is believed to play an important role in nociceptive transmission. There is increasing evidence that uncontrolled activation of microglial cells under neuropathic pain conditions induces the release of proinflammatory cytokines (interleukin – IL-1beta, IL-6, tumor necrosis factor – TNF-alpha), complement components (C1q, C3, C4, C5, C5a) and other substances that facilitate pain transmission. Additionally, microglia activation can lead to altered activity of opioid systems and neuropathic pain is characterized by resistance to morphine. Pharmacological attenuation of glial activation represents a novel approach for controlling neuropathic pain. It has been found that propentofylline, pentoxifylline, fluorocitrate and minocycline decrease microglial activation and inhibit proinflammatory cytokines, thereby suppressing the development of neuropathic pain. The results of many studies support the idea that modulation of glial and neuroimmune activation may be a potential therapeutic mechanism for enhancement of morphine analgesia. Researchers and pharmacological companies have embarked on a new approach to the control of microglial activity, which is to search for substances that activate anti-inflammatory cytokines like IL-10. IL-10 is very interesting since it reduces allodynia and hyperalgesia by suppressing the production and activity of TNF-alpha, IL-1beta and IL-6. Some glial inhibitors, which are safe and clinically well tolerated, are potential useful agents for treatment of neuropathic pain and for the prevention of tolerance to morphine analgesia. Targeting glial activation is a clinically promising method for treatment of neuropathic pain.

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Microglia: a promising target for treating neuropathic and postoperative pain, and morphine tolerance.

Source

Department of Anesthesiology, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA.

Abstract

Management of chronic pain, such as nerve-injury-induced neuropathic pain associated with diabetic neuropathy, viral infection, and cancer, is a real clinical challenge. Major surgeries, such as breast and thoracic surgery, leg amputation, and coronary artery bypass surgery, also lead to chronic pain in 10-50% of individuals after acute postoperative pain, partly due to surgery-induced nerve injury. Current treatments mainly focus on blocking neurotransmission in the pain pathway and have only resulted in limited success. Ironically, chronic opioid exposure might lead to paradoxical pain. Development of effective therapeutic strategies requires a better understanding of cellular mechanisms underlying the pathogenesis of neuropathic pain. Progress in pain research points to an important role of microglial cells in the development of chronic pain. Spinal cord microglia are strongly activated after nerve injury, surgical incision, and chronic opioid exposure. Increasing evidence suggests that, under all these conditions, the activated microglia not only exhibit increased expression of microglial markers CD 11 b and Iba 1, but also display elevated phosphorylation of p38 mitogen-activated protein kinase. Inhibition of spinal cord p38 has been shown to attenuate neuropathic and postoperative pain, as well as morphine-induced antinociceptive tolerance. Activation of p38 in spinal microglia results in increased synthesis and release of the neurotrophin brain-derived neurotrophic factor and the proinflammatory cytokines interleukin-1β, interleukin-6, and tumor necrosis factor-α. These microglia-released mediators can powerfully modulate spinal cord synaptic transmission, leading to increased excitability of dorsal horn neurons, that is, central sensitization, partly via suppressing inhibitory synaptic transmission. Here, we review studies that support the pronociceptive role of microglia in conditions of neuropathic and postoperative pain and opioid tolerance. We conclude that targeting microglial signaling might lead to more effective treatments for devastating chronic pain after diabetic neuropathy, viral infection, cancer, and major surgeries, partly via improving the analgesic efficacy of opioids.

 

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The material on this site is for informational purposes only, and is not a substitute for medical advice,
diagnosis or treatment provided by a qualified health care provider.
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For My Home Page, click here:  
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Ketamine Intranasal for Rapid Relief of Pain and Depression

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Poorly managed pain can evolve into chronic disease of the nervous system

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Ketamine is an important analgesic, more important than opioids. It can dramatically reduce pain, and rapidly relieve depression and PTSD.  Please read my earlier posts here and here. And the NPR report here just after I posted this (skip to their last section). Yes, it is FDA approved and legal. One woman said:

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 ’It was almost immediate, the sense of calmness and relaxation.

‘No more fogginess. No more heaviness. I feel like I’m a clean slate right now. I want to go home and see friends or, you know, go to the grocery store and cook the family dinner.’

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NPR again reports ketamine’s rapid relief of depression. A 28 year old man whose refractory depression began at age 15, after ketamine, says:

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‘I Wanted To Live Life’

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Stephens himself has vivid memories of the day he got ketamine. It was a Monday morning and he woke up feeling really bad, he says. His mood was still dark when doctors put in an IV and delivered the drug.”Monday afternoon I felt like a completely different person,” he says. “I woke up Tuesday morning and I said, ‘Wow, there’s stuff I want to do today.’ And I woke up Wednesday morning and Thursday morning and I actually wanted to do things. I wanted to live life.”.
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Since then, they treated him with Riluzole that is FDA approved for ALS and has one of the dirtiest side effect profiles I have ever seen in medicine with serious organ toxicity. Ketamine rarely causes mild transient side effects, usually none. It appears the concern is how ketamine is used on the street with potential for abuse. I do not see ketamine abuse in my patients, some of whom are on opioids for pain or Valium family medicines from their psychiatrist. All of those have a greater potential for abuse, also not occurring in my patients. Pain and/or depression can lead to suicide.
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About 18 months ago, researchers at Yale found a possible explanation for ketamine’s effectiveness. It seems to affect the glutamate system in a way that causes brain cells to form new connections.
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Researchers have long suspected that stress and depression weaken some connections among brain cells. Ketamine appears to reverse the process.

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It would be of interest to see a case report of the bladder problems they mention. Is this in a single drug addict who used many unknown medications on the street? Several physicians have infused IV ketamine for persons with pain for many years, in far higher doses than I prescribe, with no report of any but transient minor symptoms.

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David Barsook’s 2009 review, reference below, describes changes that cause memory loss and brain atrophy with chronic pain, in particular, Complex Regional Pain Syndrome (CRPS), and they also occur with chronic depression:

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With the onset of chronic pain (including CRPS) a number of changes in brain function occur in the human brain including but not limited to: (1) central sensitization ; (2) functional plasticity in chronic pain and in CRPS; (3) gray matter volume loss in CRPS ; (4) chemical alterations; and (5) altered modulatory controls. Such changes are thought to be in part a result of excitatory amino acid release in chronic pain. Excitatory amino acids are present throughout the brain and are normally involved in neural transmission but may contribute to altered function with excessive release producing increased influx of calcium and potentially neural death.

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Brain atrophy and memory loss has also been shown in chronic low back pain as well as in chronic depression.

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Barriers to management of chronic pain are many:

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Although opioids are effective for acute pain, effective treatment of chronic pain is often daunting, particularly neuropathic pain.

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Opioids have been shown to create pain causing imbalance in the glial cytokines that favor pain rather than relief of pain. Opioids carry the risk of opioid-induced hyperalgesia which is a severe pain sensitivity. They affect the brain and endocrine system. Opioids may fail to offer significant relief, fail to improve function, and risk misuse, abuse, diversion and death. Their costs are astronomic, insurance coverage is increasingly limited, the potential for complications may be life threatening in a hectic medical setting, side effects can be lethal, lack of physician training in use of opioids and alternatives to pain control lead to increasing deaths, addiction and diversion. It has become a national emergency and a trillion dollar war on drugs.

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Complications can be greatly reduced through use of a scrupulous history and physical examination, but reimbursement is directly proportional to the shortest time spent with a patient. Will that help assessment and care?

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Individuals may have dramatically different responses to opioid therapy; some may not tolerate any, and relief must be balanced with side effects that increase as the dose increases. Patient status may change and require IV, rectal or tube delivery instead of oral formulas; drug-drug interactions may require rapid changes, and disease of kidney, liver or brain may require modifications or stopping altogether. They may increase risk of falls and cause central sleep apnea with drop in oxygen because the brain fails to give a signal to breathe.

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Chronic pain can lead to loss of sleep, hopelessness, depression, anger and other mood disorders such as panic, anxiety, hypochondriasis and post traumatic stress disorder [PTSD]. Treatment of mood disorders are shown to profoundly reduce pain perception and/or ability to cope with pain.

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Ketamine is anti-inflammatory and can reduce the need for opioid use, thus reducing the pain and side effects caused by opioids.

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Nasal ketamine is more effective than oral ketamine for pain relief; oral dosing has no effect on depression.

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Nasal delivery of ketamine is now possible due to advances in metered nasal sprayers that deliver a precise dose. No needle is required, no IV access, no travel to a specialist needed.

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You can carry pain relief with you and use it as directed when it is needed.

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Ketamine is an NMDA antagonist: it antagonizes the NMDA receptor which plays a profound role in pain systems and centralization of pain.

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Ketamine is neuroprotective and it can help other disease states  as noted by Barsook, 2009:

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Besides improvement in pain, “there may be lessons from other diseases that affect the brain; it is noteworthy that acute ketamine doses seem to reverse depression and ketamine decreased prevalence of post-traumatic stress disorder (PTSD) in soldiers receiving ketamine during their surgery for treatment of their burns. In addition ketamine attenuates post-operative cognitive dysfunction following cardiac surgery that has been known to produce significant changes in cognition. [emphasis mine] The data suggest that the drug can alter or prevent other conditions based on its NMDAR activity where other drugs NMDA receptor antagonists are perhaps not as effective in these or pain conditions. Lastly, NMDA antagonists have been used in degenerative disease (and pain may be considered a degenerative disease as defined by loss of gray matter volume, see above) with mixed effects perhaps relating to how they act on specific NMDA subtypes. Taken together, ketamine may act not only on sensory systems affecting pain intensity, but also on a constellation of brain regions that are involved in the pain phentype. [sic, phenotype]“

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Side Effects

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Ketamine is more frequently used in babies and children than in adults because high doses of ketamine can induce hallucinations in the adult. Importantly, it is used in high dose in adults for treatment of Complex Regional Pain Syndrome.

Low doses, cause little or no side effects in adults. If present, they are transient and often resolve in 20 minutes. Patient who respond to ketamine report good acceptance as they find the relief of pain and/or depression far outweighs any short term minimal discomfort.

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Pain care reform is urgently needed.

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Research funding for pain is less than half of one percent of the NIH budget. More research is needed, but research on low dose ketamine for treatment of pain and depression has gone on for twenty years.

The public health crisis of untreated pain, which often results in disability, parallels the country’s struggle to halt the cost of health care. The longer a person remains with untreated pain, the less likely they are to return to work or to be employable.

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Conclusion

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Pain control requires urgent attention. It is past time to put into practice the use of this valuable medication so people can get on with life instead of being mired in chronic pain that for many risks suicide and ensures continuing decades of disability. Academic studies are usually limited by defining a predetermined dose rather than clinically titrating to effect. Thus no surprise, they find no effect as every patient will have no response until they reach their dose. And that dose, in my experience, falls into a bell shaped curve. One size does not fit all. Some respond at very low dose, others require much more, and the majority fall between.

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In my experience prescribing ketamine for ten years, only a rare person has problems. Almost all find it has returned function or significantly relieved pain. Some have been able to entirely eliminate opioids that did nothing for their pain for decades, though they dutifully returned to the MD every month to chronicle that pain. Pain continued to be rated ten on a scale of ten; patient always compliant despite side effects of constipation and often depression. My patients find the benefits of nasal ketamine far outweigh the relief of oral ketamine and at much lower doses with fewer side effects.

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Further, while the pain relief may be short lived, some find it gets better with repeat dosing, and relief of depression may last one to two weeks with a single dose.

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References

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http://www.wjgnet.com/1007-9327/10/1028.asp  Ketamine suppresses intestinal NF-kappa B activation and proinflammatory cytokine in endotoxic rats.

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CONCLUSION: Ketamine can suppress endotoxin-induced production of proinflammatory cytokines such as TNF-a and IL-6 production in the intestine. This suppressive effect may act through inhibiting NF-kappa B.

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http://informahealthcare.com/doi/abs/10.1080/J354v16n03_03  Ketamine as an Analgesic Parenteral, Oral, Rectal, Subcutaneous, Transdermal and Intranasal Administration

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Ketamine is a parenteral anesthetic agent that provides analgesic activity at sub-anesthetic doses. It is an N-methyl-D-aspartate (NMDA) receptor antagonist with opioid receptor activity. Controlled studies and case reports on ketamine demonstrate efficacy in neuropathic and nociceptive pain. Because ketamine is a phencyclidine analogue, it has some of the psychological adverse effects found with that hallucinogen, especially in adults. Therefore, ketamine is not routinely used as an anesthetic in adult patients. It is a frequently used veterinary anesthetic, and is used more frequently in children than in adults. The psychotomimetic effects have prompted the DEA to classify ketamine as a Schedule III Controlled Substance. A review of the literature documents the analgesic use of ketamine by anesthesiologists and pain specialists in patients who have been refractory to standard analgesic medication regimens. Most reports demonstrate no or mild psychotomimetic effects when ketamine is dosed at sub-anesthetic doses. Patients who respond to ketamine tend to demonstrate dramatic pain relief that obviates the desire to stop treatment due to psychotomimetic effects (including hallucinations and extracorporeal experiences). Ketamine is approved by the FDA for intravenous and intramuscular administration. Use of this drug by the oral, intranasal, transdermal, rectal, and subcutaneous routes has been reported with analgesic efficacy in treating nociceptive and neuropathic pain.
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http://www.ncbi.nlm.nih.gov/pubmed/15109503  Safety and efficacy of intranasal ketamine for the treatment of breakthrough pain in patients with chronic pain: a randomized, double-blind, placebo-controlled, crossover study  Daniel Carr, et al, 2004
Crossover, 20 patients. Ketamine reduced breakthrough pain within 10min of dosing, lasting up to 60min
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http://www.ncbi.nlm.nih.gov/pubmed/15288418  Safety and efficacy of intranasal ketamine in a mixed population with chronic pain
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The intranasal route for ketamine administration has been applied only for pain of dressing changes in a single case study (Kulbe, 1998). In this patient, oxycodone and acetaminophen were ineffective to control pain during burn dressing changes in a 96-year-old woman cared for at home. She tolerated the burn dressing changes after three intranasal sprays of 0.1 ml each, in rapid succession, each containing 5 mg ketamine (15 mg total) (Kulbe, 1998).
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http://www.acutepainjournal.com/article/S1366-0071%2807%2900167-2/abstract  Safety and efficacy of intranasal ketamine for acute postoperative pain
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Ketamine delivered intranasally was well tolerated. Statistically significant analgesia, superior to placebo, was observed with the highest dose tested, 50 mg, over a 3 h period. Rapid onset of analgesia was reported (<10 min), and meaningful pain relief was achieved within 15 min of the 50 mg dose. The majority of adverse events were mild/weak and transient. No untoward effects were observed on vital signs, pulse oximetry, and nasal examination. At the doses tested, no significant dissociative effects were evident using the Side Effects Rating Scale for Dissociative Anaesthetics.
The safety profile following treatment with ketamine was comparable to that seen with placebo.
Although patients did report side effects of fatigue, dizziness and feelings of unreality more often following treatment with ketamine than following treatment with placebo, no patient reported hallucinations and the side effects were generally reported to be of mild or moderate severity, and transient. No serious adverse events were reported and the incidences of associated adverse events were comparable for ketamine and placebo. Although study medication was administered intranasally, nasal signs and symptoms were few and inconsequential. A distinctive taste, however, was reported more often following treatment with ketamine than following treatment with placebo.In conclusion this randomized, placebo-controlled, double-blind study, in 20 patients, has demonstrated that intranasal ketamine is safe and effective for BTP [breakthrough pain]. Our findings augment an early but promising literature documenting the effectiveness of nasal administration of a variety of opioids for pain management in adults (Dale et al., 2002) .
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~http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2875542/

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2875542/  Ketamine and chronic pain – Going the distance, David Barsook, 2009

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This important paper covers essential points not mentioned by many, thus quoted at length below:

“Ketamine, brain function and therapeutic effect – neuroprotective or neurotoxic

With the onset of chronic pain (including CRPS) a number of changes in brain function occur in the human brain including but not limited to: (1) central sensitization ; (2) functional plasticity in chronic pain and in CRPS; (3) gray matter volume loss in CRPS ; (4) chemical alterations ; and (5) altered modulatory controls. Such changes are thought to be in part a result of excitatory amino acid release in chronic pain. Excitatory amino acids are present throughout the brain and are normally involved in neural transmission but may contribute to altered function with excessive release producing increased influx of calcium and potentially neural death. Here lies the conundrum the use of an agent that potentially deleteriously affect neurons that may already be compromised but may also have neuroprotective properties by mechanisms that include reducing phosphorylation of glutamate receptors resulting in decreased glutamatergic synaptic transmission and reduced potential excitotoxicity . Alternatively, ketamine may affect glia regulation of glutamate and inhibit glutamate release within glia. However, by whatever mechanism ketamine acts on CRPS pain, there does seem to be a dose/duration effect in that longer doses at levels tolerated by patients seem to prove more effective in terms of the duration of effects.

So what could be happening in the brain and what is required to alter brain systems and reverse the symptomatic state? Ketamine may diminish glutamate transmission and “resets” brain circuits, but it seems that a minimal dose and/or duration of treatment is required. Alternatively, ketamine may produce neurotoxicity and damage or produce a chemical lesion of affected neurons. These two issues are important to be understood in future trials. Reports from patients who have had anesthetic doses have included prolonged pain relief for many months. While the authors did not address issues such as the effect of dosing duration or repetitive dosing at say 6weeks, they did show a level of efficacy based on NNT that equals or betters most drug trials for this condition.”

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“Conclusions

As a community we have a major opportunity to define the efficacy and use of a drug that may offer more to CRPS (and perhaps other) patients than is currently available. This is clearly an opportunity that needs urgent attention and a number of questions remain to be answered. For example, is ketamine more effective in early stage disease? How does ketamine provide long-term effects? Further controlled trials evaluating dose, duration, anesthetic vs. non-anesthetic dosing are needed. Few of us really understand what it is like to suffer from a chronic pain condition such as CRPS. Ketamine therapy may be a way forward that can be brought into our clinical practice through further controlled studies that will allow for appropriate standards for use in patients.”

 

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The material on this site is for informational purposes only, and is not a substitute for medical advice,
diagnosis or treatment provided by a qualified health care provider.
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For My Home Page, click here:  Welcome to my Weblog on Pain Management!
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Pain and the Immune System – It’s Not Just About Neurons – Naltrexone

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The Immune System and Pain

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There is a whole new way of thinking of about pain that has nothing to do with pain being

transmitted by nerve cells in well defined nerve pathways.

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In the last few years, we have learned it has to do with activation of glia and the immune system.

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Pain is a central neuroimmune activation.

There is close interaction of nerve pathways and the central immune system.

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Neuroimmune responses parallel but do not always mirror peripheral immune responses.

The differences are critical.

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The science of understanding immune cell-glia and glia-neuronal interactions is in its infancy.

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What are glia?

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Glia are cells in the central nervous system (CNS), the brain and spinal cord. Ninety percent of the cells in the CNS are glia – microglia, astrocytes, oligodendroglia, perivascular glia. Glia outnumber neurons by a factor of 10 to 1.

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Microglia and astrocytes are immune cells that can release inflammatory responses with harmful effects on nerve cells such as inflammation, toxicity, and excitability. However, scientists are beginning to show that activation may also lead to good outcomes that are helpful for nearby glia and neurons, protecting against inflammation, toxicity and restoring normal pain signaling. In other words, they can restore balance.

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Beneficial and pathological microglia

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Neuroinflammation is a normal and necessary process in the acute phase, but not when it takes on a life of its own and creates persistent pain or disease directed against normal tissue (autoimmune response). They may fail to release protective agents (e.g. BDNF, Brain-Derived Neurotrophic Factor).

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Neuron-glia Tetrapartite Synapse

Glial activation from pro-inflammatory to anti-inflammatory state

(click image to enlarge)

Image from Milligan, E, Watkins, L. Pathological and Protective Roles of Glia in Chronic Pain,

Nature Reviews 10:23-36 (2009)

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Neuroinflammatory Disorders

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There is an growing body of evidence that shows many diverse diseases are characterized by neuroinflammation, such as Alzheimers, Parkinson’s Disease, ALS, Multiple Sclerosis, neuromuscular and myofascial syndromes and neuropathic pain, fibromyalgia, and chronic fatigue syndrome. Our research plans to show activation of glia in other conditions: Tourette’s Syndrome, dystonia, blepharospasm, and torticollis. A neuronal model no longer works to explain these conditions.

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What the heck is microglial activation and priming?

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How do glia become activated? They are always active, not activated but active, surveying their environment. Something must occur for them to become activated. Similar to a bee sting that primes your immune system, the first bee sting will not kill the person who is allergic, but BOOM! the second sting can kill. Glia can become primed by a first pain, but when pain next occurs, glia become activated and they respond faster, harder, longer.

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When activated, they change shape like amoeba and migrate to the site of injury or infection or stroke or dead cells where they proliferate, release cytokines, and phagocytose (consume) targets such as virus, dead tissue, important in wound healing. Microglia and astrocytes can release neuroexcitatory and pro-inflammatory products and growth factors for pain and hyperalgesia. See links to several recent publications on glia here, and mechanisms here and here. Microglia can repair the CNS. Or, an injury may heal and be long gone, but chronic pain may persist for years. How do we turn it off? The signal is no longer telling us about a new danger.

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The goal of research is to find ways to interact with the cascades of pro-inflammatory molecules and receptors to restore balance in the system. This is a major paradigm shift in treatment of chronic pain that has already led to many insights. Refer articles here.

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Toll Like Receptors

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Like all immune competent cells, glia have a myriad of receptors on their cell surface membranes. One of the more important are the Toll Like Receptors (TLRs) that are innate immune receptors in the CNS, discussed here. See image, below. TLRs “are key regulators of both innate and adaptive immune responses. The function of TLRs in various human diseases has been investigated….These studies have shown that TLR function affects several diseases, including sepsis, immunodeficiencies, atherosclerosis and asthma…. [They] may contribute to susceptibility to severe neonatal inflammatory diseases, allergies, and autoimmune diseases.” Other studies have shown “Toll-like receptors (TLRs) are essential in the host defense against infections. They also have functional roles in tumor progression and their ligands affect tumor cell proliferation, anti-apoptosis and immune escape. The expression or up-regulation of TLRs has been detected in various tumor cells.” “Dysregulation of these signaling pathways has severe consequences, and causes many autoimmune diseases and chronic pathological inflammation.”

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The Toll Like Receptors are not like other receptors. Not these snug little pockets where naltrexone binds. Instead the Toll Like Receptors are like an entire football field, with enormous nooks and crannies. Unlike other receptors, they have enormous interactions with many molecules and medications, e.g. naltrexone is a TLR4 inhibitor, an immune modulator, amitriptyline is a TLR4 inhibitor. And Glial activation is now known to occur in response to opioids as well. Opioid-induced glial activation opposes opioid analgesia and enhances opioid tolerance, dependence, reward and respiratory depression.” That source is referenced here. Opioids create pain, not just the dread opioid induced hyperalgesia. Glia also contain cannabinoid receptors. Glia produce endogenous cannabinoids and they inactivate them.

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Toll-Like Receptors.

(Image courtesy of SABiosciences, click to enlarge)

Their action on IL-10 is key and more on that will be posted here later.

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Antibodies for pain?

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Some pain syndromes have been found to produce distinct antibodies.

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There is small but growing evidence that the immune system plays a role in Complex Regional Pain Syndrome, CRPS. These individuals have inflammatory markers in spinal fluid and tissue fluids. Recent studies have found antibodies against nervous system structures, specifically, “autoantibodies against an inducible autonomic nervous system autoantigen” in 30 to 40% of persons with CRPS.

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In 2010, a small study found that intravenous immunoglobulin (IVIG) can provide relief in a tiny percentage of patients. IVIG potentially interferes with those autoantibodies and reduces, i.e. downregulates, the inflammatory cytokines that are important in mechanisms of pain and hyperalgesia in the brain and the body. This study has many limitations but it is a first for IVIG.

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JJ Van Hilten et al have found HLA antigens associated with Complex Regional Pain Syndrome with fixed dystonia. “Our results encourage future studies to evaluate the role of HLA-B62 and HLA-DQ8 in different subtypes of CRPS.” This gene family has important immunologic functions.

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And, epidemiology studies show that persons with CRPS are more likely to have asthma.

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The study of glia is in its infancy but it is growing rapidly in many directions. There are drugs that can distinguish activated glia for targeted treatment, new methods of visualizing glia, new sites for pharmacologic intervention, and nanotechnology to deliver medication directly to the inflammation. ` More will come provided there is philanthropic support for this work. It is heartbreaking that NIH contributes less than 1% of its research dollar to pain.

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My thanks to the Reflex Sympathetic Dystrophy Syndrome Association, RSDSA.org, for sponsoring a workshop on Glia and Neuroinflammation that brought together the world’s foremost scientists and provided a unique forum for them to interact and learn from each other.

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It is hoped that their next workshop this year will be on imaging glia. We need to extend the work that has barely begun.`

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The material on this site is for informational purposes only.

It is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider.

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For My Home Page, click here:  Welcome to my Weblog on Pain Management!

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LDN World Database – Low Dose Naltrexone

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This is a database of persons who have tried low dose naltrexone, their diagnosis, dosage and response to it, if any. The database lists many different medical conditions.

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For example, persons with Multiple Sclerosis, will choose the link above, that has hundreds of persons with MS who have tried naltrexone. Don’t forget to see more pages once you reach the bottom. For a graph of the overall responses, then go back to the main link on Multiple Sclerosis where you see these choices:

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To view the database please click HERE

To view the Graph on how people feel about LDN please click HERE

To add your experience with LDN please click HERE – of course first select the condition you have, so your entry falls into the proper category.

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If your condition is different, just select the condition from the list on left.

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For example for fibromyalgia:

To view the database please click HERE

To view the Graph on how people feel about LDN please click HERE

To add your experience with LDN please click HERE

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Here for Irritable Bowel Syndrome, Crohn’s or Ulcerative Colitis.

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If your condition is not listed, check Other on the left side of the list.

This forum is from LDN Research Trust, a registered non-profit Charity based in the UK, with participants from many countries internationally.

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I will soon be posting several case reports of my patient responders, persons with intractable pain from various conditions. Some have been pain free one or two years on naltrexone. Some who had years of previously intractable pain have responded to low dose naltrexone and remained pain free more than one year after discontinuing LDN.

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MECHANISM

for those who like to know the science

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We have known for decades that naltrexone binds to the mu opioid receptor. It blocks the effect of opioids like morphine at the mu receptor. We now know it also acts at another receptor.

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You may wish to watch this video that explains Toll Like Receptors, TLRs for short. This is a lecture by Dr. Rachel Allen, whose PhD in immunology is from Oxford University. After that, she worked at Cambridge University on innate immune receptors such as the TLR’s.

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In 2008, it was shown that naltrexone binds at one of the Toll Like Receptors, the TLR4 receptor. There are 13 Toll Like Receptors, and so far they have studied naltrexone only at one of them, the TLR4. That is important because the TLR receptors are part of the innate immune system.

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The Toll Like Receptors are not like other receptors. Not these snug little pockets where naltrexone binds. Instead the Toll Like Receptors are like an entire football field, with enormous nooks and crannies where it has many interactions with many molecules. Now, in 2010, scientists are asking if naloxone or naltrexone is acting at TLR4 or even higher up in the cascade.

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The study of immune cell glial interactions is in its infancy. Glial cells are the immune cells in your central nervous system (brain, spinal cord). They are very involved in dysregulation of pain systems, neuroinflammation, and some neurological diseases such as Multiple Sclerosis, Alzheimer’s, Parkinson’s Disease, ALS, infections of the brain, etc.

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One of our distinguished glial scientists, Linda Watkins, PhD, in October 2010, said we are not even sure naltrexone binds to the Toll Like Receptor. Rather, it involves AKT1, close to the TLR4 receptor, very very high up in the cascade at the dimerization step, the recruitment of CD14. This is being worked out now.

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Dr. Watkins with Kennar Rice, PhD, from NIH/NIDA, et al, has a paper in press in Cell:

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Glial activation participates in the mediation of pain including neuropathic pain, due to release of neuroexcitatory, proinflammatory products. Glial activation is now known to occur in response to opioids as well. Opioid-induced glial activation opposes opioid analgesia and enhances opioid tolerance, dependence, reward and respiratory depression. Such effects can occur, not via classical opioid receptors, but rather via non-stereoselective activation of toll-like receptor 4 (TLR4), a recently recognized key glial receptor participating in neuropathic pain as well. This discovery identifies a means for separating the beneficial actions of opioids (opioid receptor mediated) from the unwanted side-effects (TLR4/glial mediated) by pharmacologically targeting TLR4. Such a drug should be a stand-alone therapeutic for treating neuropathic pain as well. Excitingly, with newly-established clinical trials of two glial modulators for treating neuropathic pain and improving the utility of opioids, translation from rats-to-humans now begins with the promise of improved clinical pain control.

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For chronic pain, targets of interest are: glial attenuation, p38 MAPK inhibition.

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Of interest, a commonly prescribed pain medication, amitriptyline, is a TLR4 inhibitor (Hutchinson, 2010).

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You can read many new publications on glia that I posted on my site here, or find it from the banner at top:

Donate to Eliminate Neuropathic Pain

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I am a member of a Neuroinflammation Research Consortium that will be studying these many conditions, some that are painful, others that are not. They involve glia and neuroinflammation.

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For more discussion of mechanisms of action of naltrexone and other publications I have posted, see here, particularly the paper by Zhang, Hong, Kim et al.

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Finally, for those who may feel they are losing heart because medicine has been too slow to adopt the use of low dose naltrexone, let me point this out:

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Dr. Linda Watkins is a University of Colorado Distinguished Professor of Psychology & Neuroscience at the University of Colorado Boulder. She is a world-renown leader in glia research and the neurological applications of glial attenuation, with a focus on alleviation of chronic pain. She is the recipient of the highest award for distinguished basic science research from the American Pain Society and the 2010 John Liebeskind Pain Management Research Award from the American Academy of Pain Management. She has over 300 peer-reviewed publications including articles in Nature, Science, Nature Neuroscience, and Journal of Neuroscience. She received over $2 million in NIH grants supporting 6 generations of IL-10 gene therapy research culminating in XT-101.

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The material on this site is for informational purposes only.

It is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider.

~~~~~

For My Home Page, click here:  Welcome to my Weblog on Pain Management!

RSD – CRPS – Complex Regional Pain Syndrome – Long Distance Patients

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I see long distance patients in my office who generally come for a two week stay, and I wish to encourage their comments on this page. I am sorry I did not post this page for them sooner.

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Most people I see have been tried on every common approach to treatment for Complex Regional Pain Syndrome, CRPS. I prescribe most of those therapies as well, but I also use an expanded number of neuropharmacology approaches. Some of these are outlined in the case report I filed in March 2010.

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In my opinion, it is important to use rational polypharmacy. When pain is intense, it is important to look at more than one mechanism. Once pain comes under control and remains at zero, then we can slowly begin to taper off one at a time.

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The following describe two of the several mechanisms of interest to me.

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NMDA Antagonists

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The glutamate-NMDA receptor is profoundly important in controlling pain pathways. It is responsible for tolerance to medication and centralization of pain. Research in France has shown that with chronic pain in persons with CRPS there is an increase in NMDA receptors in the central nervous system. After pain control, the increased number of NMDA receptors returns to normal.

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With persistent pain or chronic depression, glutamate increases and becomes excitotoxic. When it attaches to the NMDA receptor, it causes calcium to enter the neuron, creates free radicals, and kills neurons. This leads to brain atrophy and potentially memory loss.

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The goal is to block this mechanism. I use three medications that work at this level.

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Morphinans – Glial dysregulation of pain pathways

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Another important area of focus for me are the morphinans which means morphine-like. Their mechanism of action is at the microglia, the immune cells in the central nervous system. There is important new research on glial dysregulation of pain pathways. Once primed and activated by pain, the next pain insult causes glia to react harder, faster and longer perpetuating pain with cascades of pro-inflammatory molecules. Glial research on pain is very recent, very new, very important, and is a rapidly growing  body of science. It offers an entirely new paradigm for treatment of chronic pain.

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The Reflex Sympathetic Dystrophy Syndrome Association library has

many research articles that you may wish to read.

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I am grateful to be invited to their workshop on activated glia.

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Contributing Factors

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I look at the whole person, review all of their medications including their vitamins and botanicals, toxicity and adverse interactions with medication. I check the blood level for 25(OH) vitamin D (done at ARUP labs), parathyroid hormone (PTH) if not already done, and stress the importance of anti-inflammatory diet, fish oil, and adequate levels of vitamin D3.

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Spinal cord stimulators – controversy

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A recent Wall Street Journal article discusses some of the controversy of interventional techniques in this evolving specialty and mentions that some studies are underway to show efficacy. Implantable devices are controversial “and questions remain about the appropriateness of their use.”

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In April 2010, new guidelines were published, updating earlier ones from 1997: Practice Guidelines for Chronic Pain Management: An Updated Report by the American Society of Anesthesiologists Task Force on Chronic Pain Management and the American Society of Regional Anesthesia and Pain Medicine.

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“Spinal cord stimulation: One randomized controlled trial reports effective pain relief for CRPS patients at follow-up assessment periods of 6 months to 2 yr when spinal cord stimulation in combination with physical therapy is compared with physical therapy alone (Category A3 evidence).”

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A3 evidence was defined as: “The literature contains a single randomized controlled trial.”

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The guidelines had no references, nor did it indicate how old that study was. A short two year followup and a single limited study after more than 32 years of implanting these devices should call for more research.

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I do not recommend spinal cord stimulators as there is no research showing long term efficacy and no quality evidence showing they are superior treatment. Success declines after placement and that may occur the first day. In fact, there is one long term 5 year European study showing no efficacy after two years.

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Often patients are not aware that alternatives exist and are not given fully informed consent on the stimulators. Those risks include increased pain with any invasive procedure in persons with CRPS, paralysis, spasticity, infection, scarring, potential flare into generalized CRPS pain. The fact that these leads are permanent  - they can never be removed – means that person can never undergo MRI scans in future even if they should have cancer or stroke. The leads become scarred into nerve tissue.

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A colleague, a prominent Harvard trained anesthesia pain specialist in practice for 37 years, declines to recommend stimulators or pumps for that reason: there is no long term data proving efficacy.

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Complications of spinal cord stimulators should be published. Perhaps they exist. If anyone has seen them, please advise me. I tend to see the complications or the failures, but those who place them and the corporations that fund them should have a special obligation to study the complications and the long term benefits. Having a spinal cord stimulator does not prevent use of other medication but it may add to the burden of pain to overcome. Nationally there should be an audit of stimulators placed, with patient outcomes including complications and number of revisions made. The risks are too grave not to require this and the cost is too high if there is no lasting efficacy.

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The excerpt below is from a 2003 review on spinal cord stimulation (SCS) for Complex Regional Pain Syndrome. It may be outdated, however Medtronic failed to provide me with any long term studies when requested:

“The use of SCS for the treatment of pain in CRPS (including RSD and causalgia) has been reported in the literature for over 25 years. The consensus opinion from experts suggests that SCS should be considered in the treatment algorithm when conservative or traditional therapies have failed. However, such considerations are not based on reliable evidence generated through well-designed randomized controlled trials. To date, there has not been a systemic evaluation of the existing literature concerning the efficacy of SCS for patients with CRPS.”

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For those interested in coming to San Diego for two week stay, please see information on long distance patients in banner at top of page.

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I hope my patients who have come from long distance who stayed nearby for two weeks will feel free to comment on their experience.

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~~~~~The material on this site is for informational purposes only, and is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider. ~~~~~

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