http://pmj.bmj.com/content/87/1028/410.full.pdf
You may have to read this a few times to really “get it” but this piece was written for doctors by a TN specialist / Neuroscientist from The UK.
Specifically read the part under " Pathogenesis"
As to your questions there is NO one cause…there are several proven causes and some that are suspected…and then in some cases cause is unknown.
Here is another thing I copy/pasted but lost where I got it from…
“The role, if any, of remyelination in initial symptomatic recovery after microvascular decompression is unclear. Clearly, remyelination cannot account for the immediate relief from neuralgia. In the longer term, however, it is possible that remyelination helps to ensure that relief of symptoms is sustained. Remyelination may also be responsible for spontaneous remission of trigeminal neuralgia in some patients. Failure of microvascular decompression to relieve symptoms is most common in patients with very long-standing disease, in whom severe local depletion of oligodendrocytes and astrocytes may prevent effective remyelination after decompressive surgery. A further possibility is that the aberrant remyelination that is occasionally seen in the compressed nerve root (Love et al., 1998) may, by preventing the separation of groups of apposed axons after decompression, contribute to the failure of this procedure in a few patients.”
The following was taken from The Facial Pain Foundation…really interesting.
Dr. Mark Linskey is a Professor of Neurological Surgery currently practicing at the University of CA, Irvine, in Orange County, CA (http://www.faculty.uci.edu//profile.cfm?faculty_id=5322). He trained in microvascular decompression (MVD) for 7 years with Peter Jannetta and in Gamma Knife stereotactic radiosurgery (GKSR), glycerol rhizotomy and radiofrequency lesioning for 7 years with L Dade Lunsford at the first US gamma Knife unit at the University of Pittsburgh. He has continuously served on the Medical Advisory Board of TNA - The Facial pain association since 2003; currently serving as their Western Regional Director. In practice and out of training for more than 20 years, he published the first prospective cohort comparative clinical trial of MVD versus GKSR for typical trigeminal neuralgia and is an internationally-recognized expert, and experienced surgical subspecialist, in trigeminal neuralgia. He is currently the American College of Physicians (ACP) Trigeminal Neuralgia module editor for their physician point of care decision support tool “Smart Medicine” (formerly PIER - Physician Information & Education Resource). He is also the Co-Editor of the Trigeminal Neuralgia module for the rigorous evidence-based medicine periodic systematic review tool and physician decision-support resource, “Clinical Evidence”, published by the BMJ (British Medical Journal) for the British Medical Association.
Facial Pain The Research Imperative
By Mark E. Linskey, M.D.
From a twisted and perverse perspective, among facial pain patients, patients with classical trigeminal neuralgia (TN), are comparatively fortunate. We at least have surgical treatment options with reasonable chances for successful pain relief when current medical therapy fails. Yet even for TN patients, not all patients fare well. While in expert and experienced surgical hands, microvascular decompression (MVD) can lead to durable complete pain relief in about 80% of patients, this still leaves one in five TN patients still suffering. Patients seeking care in the general medical community are not so fortunate. MVD results can vary significantly surgeon-to-surgeon. Empiric experience over the last 20 years in my practice, would suggest that the success rate among less experienced and expert surgeons might run as low as 50%.
For those patients with multiple sclerosis-related TN, or who fail MVD, their plight can be improved with palliative destructive procedures directed towards the trigeminal nerve [stereotactic radiosurgery (SR, radiofrequency lesioning (RFL), glycerol rhizotomy (GR), and balloon compression (BC)]. However, these procedures serve best as temporizing measures, with up to 50% of patients with classical TN recurring within five years of the procedure. Each palliative destructive procedure runs the risk of facial numbness with its associated risk of new de-afferentation pain from nerve damage, and these risks accumulate and compound as destructive procedures are repeated. Thus overall, across the U.S., even for patients with classical TN, surgical intervention may realistically not provide adequate or long-lasting relief in an estimated 30-50% of cases.
But what about those patients with other forms of facial pain? In 2008, after 18 years of existence, The Trigeminal Neuralgia Association (TNA) changed its name to TNA – The Facial Pain Association (TNA-FPA) in recognition of the fact that patients with facial pain other than classical TN also needed education, support and help too. These conditions include TN2, neuropathic facial pain, facial pain of obscure etiology, and anesthesia dolorosa, among many others. For these patients, MVD rarely leaves a patient pain-free. Furthermore, while palliative destructive procedures can, and do help, they not only are less successful than for classical TN patients, they may actually worsen the situation through increased de-afferentation, despite the best of surgical intentions. While surgical stimulator surgery can help these patients in very select cases, the overall percentage of patients enjoying significant and durable relief is disappointingly small. If we now broaden our inquiry to include all facial pain patients that seek help from TNA-FPA, it seems likely that only about half will achieve adequate or long-lasting relief from their suffering through surgery. Clearly surgery alone is not the answer for too many of our patients, friends, and family who suffer from facial pain.
The word imperative refers to something that is both necessary and of vital or crucial importance. It may also refer to the expression of a command. For facial pain syndromes new discovery and therapeutic breakthroughs through basic science research is an absolute imperative in the first sense and an imperative from our patients and their loved ones in the second sense.
We know that vascular compression is a necessary cause for the majority of classical TN patients. Yet up to 40% of normal living patients and up to 50% of patients studied at autopsy have these vascular contacts without having TN. Clearly vascular compression, while necessary, is not sufficient. The logical additional factor, that many have speculated about, likely involves additional predispositions related to genetics and/or the biology of myelin nerve insulation, axonal damage, or both. In my opinion, studies of deferential gene expression comparing classical TN patients to normal population controls carry the highest chance of uncovering potentially new fruitful areas for investigation and future therapeutic exploitation for patients with classical TN.
While the hoped for discoveries from studying differential gene expression in cases of classical TN might be more generalizable to help patients with other facial pain syndromes, this is by no means certain. Thus, simultaneous additional lines of research inquiry are also desperately needed. These include the urgent need for a better understanding of the neurochemistry and the psycho-biology of chronic neuropathic pain and the fast-track development of new agents for clinical testing. It includes studies into the biology of nerve repair and regeneration, through both pharmacological means as well as potential cellular therapies including stem cells. It also includes the need to study safe means of modulating pain perception at the brain level through brain stimulation technology.
While it is simple and conceptually satisfying to talk about the search for one “cure”, this may be an elusive goal given the heterogeneity and wide variety of facial pain syndromes suffered by patients seeking help through the TNA-FPA. More than one “cure” may be needed depending on the individual circumstances of each patient. Yet the quest for a “cure”, whether one or many, all still depend on basic science research advances which are expensive and which take years to develop, test and realize.
As a surgeon, I long for the day when we have therapies that can increase our MVD results to near 100% success, as well as offer hope and more predictable treatment success chances to our non-classical TN facial pain patients. While I am biased by my surgical background, I doubt that these advances will involve a new pill distributing an agent non-specifically throughout our body. I strongly suspect that they will involve therapies that will be most effective locally and selectively at the site of pathology or damage, either through direct open surgical application, or needle or electrode delivery into the trigeminal nerve root, ganglia, or brain. Thus surgery will likely be an important component of any success realized through our research efforts.
If we wish the state of care for patients with facial pain to improve from the levels currently available, we are indeed faced with a research imperative. The need is great and the costs are considerable. The best way that most can help is through generous donation and ongoing, sustained, support for efforts such as those fostered by our own Facial Pain Research Foundation http://www.facingfacialpain.org/ . We need everyone’s help and support to drive this mission forward and ultimately succeed.