Postherpetic neuralgia (PHN) is the most common and devastating complication of acute herpes zoster (HZ). Typically, the neuralgia is confined to a dermatomic area of the skin and follows an outbreak of herpes zoster (HZ, commonly known as shingles) in that same dermatomic area. Overview; Presentation; DDx; Workup; Treatment . (Our schedule does include several breaks.) Different topics will be explored in detail using home-study guideline questions and detailed answers with comments from faculty. During those 4 years, numerous treatments were tried, including systemic opioid analgesics and anticonvulsants, and topical lidocaine and capsaicin, all with unsatisfactory results. There are some sporadically successful experimental treatments, such as rhizotomy (severing or damaging the affected nerve to relieve pain) and TENS (a type of electrical pulse therapy). Neurodestructive procedures are not recommended as they enhance destruction and neuropathic pain.
The damage causes nerves in the affected dermatomic area of the skin to send abnormal electrical signals to the brain. The demographics of trigeminal neuralgia are that it occurs most often in people over the age of 50, although it can occur at any age according to the sources. A key factor in the neural plasticity underlying neuropathic pain is altered gene expression in sensory dorsal root ganglia (DRG) neurons. Gallium has significant anti-inflammatory activity, inhibiting the activation and proliferation of pro-inflammatory T cells. Following nerve damage, NaC channel accumulation causes hyperexcitability, downregulation of the TTX-resistant Nav1.8 (sensory neuron specific, SNS1) channel and upregulation of TTX-sensitive Nav1.3 (brain type III) channels. These changes contribute to increased NMDA glutamate receptor-dependent excitability of spinal dorsal horn neurons and are restricted to the ipsilateral (injured) side. A combination of these factors could contribute to the neuropathic pain state of PHN.
(see also Neuralgia, trigeminal) 350.1. Classes of Drugs: I. If patients do develop postherpetic neuralgia, they are also advised to see their doctor immediately. They may have to work with their doctor and sometimes other specialists such as neurologists to try a variety of treatments before they find something that helps. These findings are not predictive of the PHN clinical course. Viral culture or immunofluorescence staining may be used to differentiate herpes simplex from herpes zoster in cases that are difficult to distinguish clinically. Many, many other types of neuralgias exist.
A 4-fold increase has been used to support the diagnosis of subclinical herpes zoster (zoster sine herpete). However, a rising titer secondary to viral exposure rather than reactivation cannot be ruled out. Antiviral agents, such as famciclovir, are given at the onset of attacks of herpes zoster to shorten the clinical course and to help prevent complications such as postherpetic neuralgia. However they have no role to play following the acute attack if postherpetic neuralgia has become established. Analgesics Locally applied topical agents Aspirin mixed into an appropriate solvent such as diethyl ether may reduce pain. Lidocaine skin patches. Multiple sclerosis (MS) is a disease that is caused by the degradation of myelin. III.
Patches containing lidocaine can also be used on the face, taking care to avoid mucus membranes e.g. eyes, nose and mouth. Pain modification therapy Antidepressants. These drugs affect key brain chemicals, including serotonin and norepinephrine, that play a role in both depression and how your body interprets pain. Doctors typically prescribe antidepressants for postherpetic neuralgia in smaller doses than they do for depression. Low dosages of tricyclic antidepressants, including amitriptyline, seem to work best for deep, aching pain. They don’t eliminate the pain, but they may make it easier to tolerate.
Other prescription antidepressants (e.g. venlafaxine, bupropion and selective serotonin reuptake inhibitors) may be off-label used in postherpetic neuralgia and generally prove less effective, although they may be better tolerated than the tricyclics. Anticonvulsants. Postherpetic neuralgia. They have central effects on pain modulation. Medications such as phenytoin (Dilantin, Phenytek), used to treat seizures, also can lessen the pain associated with postherpetic neuralgia. The medications stabilize abnormal electrical activity in the nervous system caused by injured nerves.
Doctors often prescribe another anticonvulsant called carbamazepine (Carbatrol, Tegretol) for sharp, jabbing pain. Newer anticonvulsants, such as gabapentin (Neurontin) and lamotrigine (Lamictal), are generally tolerated better and can help control burning and pain. In some cases, treatment of postherpetic neuralgia brings complete pain relief. But most people still experience some pain, and a few don’t receive any relief. Although some people must live with postherpetic neuralgia the rest of their lives, most people can expect the condition to gradually disappear on its own within five years. High-Concentration Capsaicin Patch Granted Orphan Drug Designation for PHN from:http://www.medscape.com/viewarticle/704117?sssdmh=dm1.489879&src=ddd On June 9, 2009, The FDA approved orphan drug designation for a high-concentration capsaicin dermal patch (Qutenza [formerly NGX-4010], NeurogesX, Inc) for the treatment of pain associated with postherpetic neuralgia (PHN). Relief of pain is possible up to three months with no to minimal[clarification needed] side effects.
Qutenza has been recently[when?] approved by the FDA for general use in PHN. Postherpetic neuralgia affects nerve fibers and skin, causing burning pain that lasts long after the rash and blisters of shingles disappear. In 1995, the Food and Drug Administration (FDA) approved the vaccine to prevent chickenpox. Its effect on PHN is still unknown. The vaccine — made from a weakened form of the varicella-zoster virus — may keep chickenpox from occurring in nonimmune children and adults, or at least lessen the risk of the chickenpox virus lying dormant in the body and reactivating later as shingles. If shingles could be prevented, postherpetic neuralgia could be completely avoided. Recently, Merck has tested a new vaccine (Zostavax) against shingles. This vaccine is a more potent version of the chickenpox vaccine.
Evidence indicates that the vaccine reduced the incidence of shingles by 51 percent. Additionally, the vaccine reduced the incidence of PHN by two-thirds compared to placebo. However, the vaccine’s protective effects diminished over the three years that most patients were followed. In December 2005, an FDA advisory committee unanimously agreed that the vaccine is safe and effective for persons over 60 years old. This was followed on 26 May 2006 by the FDA formally approving the use of the vaccine for that same age group. Further studies may demonstrate if there is benefit in patients 50–59 years old and if a booster dose is recommended. ^ “CPostherpetic Neuralgia (PHN) Therapeutics – Pipeline Assessment and Market Forecasts to 2017”. http://www.globaldata.com/reportstore/Report.aspx?ID=Postherpetic-Neuralgia-PHN-Therapeutics-Pipeline-Assessment-and-Market-Forecasts-to-2017&ReportType=Industry_Report&coreindustry=Industry_Report&Title=Pharmaceuticals_and_Healthcare. ^ Bowsher, David, MD, ScD, PhD. “Treating shingles with tricyclic antidepressants to lessen the risk of PHN”.
The Center for Shingles and Postherpetic Neuralgia. http://shingles.mgh.harvard.edu/tricyclics.htm. Retrieved 2006-05-11. ^ De Benedittis G, Besana F, Lorenzetti A (1992). “A new topical treatment for acute herpetic neuralgia and post-herpetic neuralgia: the aspirin/diethyl ether mixture. An open-label study plus a double-blind controlled clinical trial”. Pain 48 (3): 383–90.
doi:10.1016/0304-3959(92)90088-S. PMID 1594261. ^ He L, Zhang D, Zhou M, Zhu C (2008). He, Li. ed. “Corticosteroids for preventing postherpetic neuralgia”. Cochrane Database Syst Rev (1): CD005582.
doi:10.1002/14651858.CD005582.pub2. PMID 18254083. ^ Doble S (2008). “Spinal Management of patients with post-herpetic neuralgia”. Nursing Standard 22 (39): 49–56. PMID 18578133. ^ Harke H, Gretenkort P, Ladleif HU, Koester P, Rahman S (2002).
“Spinal cord stimulation in postherpetic neuralgia and in acute herpes zoster pain”. Anesthesia & Analgesia 94 (3): 694–700. doi:10.1097/00000539-200203000-00040. PMID 11867400. ^ Oxman MN, Levin MJ, Johnson GR, et al. (2005). “A vaccine to prevent herpes zoster and postherpetic neuralgia in older adults”.
N. Engl. J. Med. 352 (22): 2271–84. doi:10.1056/NEJMoa051016. PMID 15930418.
^ “Merck Zostavax Shingles Vaccine Decreases In Efficacy Over Three-Year Period, FDA Says”. FDA Advisory Committee. 2005-12-15. http://www.fdaadvisorycommittee.com/FDC/AdvisoryCommittee/Committees/Vaccines+and+Related+Biological+Products/121505_Zostavax/121505_ZostavaxP.htm. Retrieved 2006-06-15. [dead link] ^ “Merck Zostavax Shingles Vaccine Safe and Effective For Adults Over 60, Committee Says”. FDA Advisory Committee.
2005-12-16. Archived from the original on 2006-05-06. http://web.archive.org/web/20060506202436/http://www.fdaadvisorycommittee.com/FDC/AdvisoryCommittee/Committees/Vaccines+and+Related+Biological+Products/121505_Zostavax/121505_ZostavaxR.htm. Retrieved 2006-06-15. ^ “FDA Licenses New Vaccine to Reduce Older Americans’ Risk of Shingles”. United States Food and Drug Administration. 2005-05-26.
http://www.fda.gov/bbs/topics/NEWS/2006/NEW01378.html. Retrieved 2006-06-15. ^ Alper BS, Lewis PR (2000). “Does treatment of acute herpes zoster prevent or shorten postherpetic neuralgia?”. The Journal of family practice 49 (3): 255–64. PMID 10735485. – Commentary at ACPJC ^ Bowsher D (1997).
“The effects of pre-emptive treatment of postherpetic neuralgia with amitriptyline: a randomized, double-blind, placebo-controlled trial”. Journal of pain and symptom management 13 (6): 327–31. doi:10.1016/S0885-3924(97)00077-8. PMID 9204652.