History

Fact Explanation
History of vesicular eruption in an area of skin on the body. It is caused by the reactivation of dormant virus that was seeded in sensory nerves during an earlier bout of primary varicella. Along with clinical reactivation, infectious virus reappears in neurons and nerve-associated satellite cells and spreads to the skin through peripheral nerves [1].
Pain, that usually precedes the eruption and continues even after its resolution. The initial viral replication causes direct damage by neuritic inflammation on the dorsal root, resulting in necrosis, fibrosis, and destruction of nerve tissue from peripheral afferent fibers to the spinal cord. The resulting deafferentation and strengthening of existing synaptic connections between central pain pathways and peripheral Aβ fibers, would lead to chronic pain syndrome [2].
Mechanical allodynia and warm/cold allodynia. After the injury, peripheral neurons have lower activation thresholds and display exaggerated responses to stimuli [1].
History of diabetes mellitus and other immunocompromised states. Reactivation of varicella zoster virus occurs when immunity to VZV declines because of aging or immunosuppression [3].
Commonly affected areas are the chest and the face. The most common nerves involved are the thoracic nerves and the ophthalmic division of the trigeminal nerve [3].
References
  1. WOOD ALASTAIR J.J., KOST RHONDA G., STRAUS STEPHEN E.. Postherpetic Neuralgia — Pathogenesis, Treatment, and Prevention. N Engl J Med [online] 1996 July, 335(1):32-42 [viewed 11 August 2014] Available from: doi:10.1056/NEJM199607043350107
  2. PARRUTI GIUSTINO, TONTODONATI , URSINI , POLILLI , VADINI , DI MASI . Post-herpetic neuralgia. IJGM [online] 2012 October [viewed 11 August 2014] Available from: doi:10.2147/IJGM.S10371
  3. SAMPATHKUMAR P, DRAGE LA, MARTIN DP. Herpes Zoster (Shingles) and Postherpetic Neuralgia Mayo Clin Proc [online] 2009 Mar, 84(3):274-280 [viewed 12 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2664599

Examination

Fact Explanation
Evidence of cutaneous scarring in the affected area. The lesions of herpes zoster progress through stages, beginning as red macules and papules that, in the course of 7 to 10 days, evolve into vesicles and form pustules and crusts leading to scabs, which can result in scarring. Complete healing may take more than 4 weeks. [1].
Hypoesthesia in the affected area of skin. Due to fibrosis of the posterior root ganglia, and loss of cutaneous innervation, along with pathological degeneration of cell bodies and axons of primary afferent neurons [2].
Increased sweating in the affected area. Due to autonomic dysfunction which occurs as a complication of herpes zoster [1].
Low mood, loss of appetite and other features of clinical depression on mental state examination. As a result of the pain interfering with sleep and recreational activities [1].
References
  1. SAMPATHKUMAR P, DRAGE LA, MARTIN DP. Herpes Zoster (Shingles) and Postherpetic Neuralgia Mayo Clin Proc [online] 2009 Mar, 84(3):274-280 [viewed 12 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2664599
  2. PARRUTI GIUSTINO, TONTODONATI , URSINI , POLILLI , VADINI , DI MASI . Post-herpetic neuralgia. IJGM [online] 2012 October [viewed 11 August 2014] Available from: doi:10.2147/IJGM.S10371

Differential Diagnoses

Fact Explanation
Trigeminal neuralgia. It also presents with pain in an area of the face but is episodic and attacks last only seconds. episodes occur in bouts over a period of weeks or months with subsequent remission [1].
Cluster headache. It also presents with unilateral headache and facial pain associated with autonomic symptoms, but attacks occur in clusters, a cluster period lasting 6 to 12 weeks, followed by a period of remission [2].
Temporomandibular joint disorders. It also presents with facial pain but is typically triggered by jaw movements or palpation of the joint or the masticatory muscles [3].
References
  1. LOVE S.. Trigeminal neuralgia: Pathology and pathogenesis. [online] 2001 December, 124(12):2347-2360 [viewed 12 August 2014] Available from: doi:10.1093/brain/124.12.2347
  2. MAY ARNE. Cluster headache: pathogenesis, diagnosis, and management. The Lancet [online] 2005 September, 366(9488):843-855 [viewed 12 August 2014] Available from: doi:10.1016/S0140-6736(05)67217-0
  3. SICCOLI MASSIMILIANO M, BASSETTI CLAUDIO L, SáNDOR PETER S. Facial pain: clinical differential diagnosis. The Lancet Neurology [online] 2006 March, 5(3):257-267 [viewed 12 August 2014] Available from: doi:10.1016/S1474-4422(06)70375-1

Investigations - for Diagnosis

Fact Explanation
Polymerase chain reaction, immunohistochemistry, and viral culture to identify the virus. These investigations are recommended when herpes simplex ( which presents with recurrent rash and sacral lesions) must be ruled out and for patients with atypical lesions [1].
References
  1. DWORKIN R. Diagnosis and Assessment of Pain Associated With Herpes Zoster and Postherpetic Neuralgia. The Journal of Pain [online] 2008 January, 9(1):37-44 [viewed 12 August 2014] Available from: doi:10.1016/j.jpain.2007.10.008

Management - General Measures

Fact Explanation
Tricyclic antidepressants. Amitriptyline: 65-100 mg 6 hourly for 3 weeks. TCAs have an analgesic action by blocking the reuptake of serotonin and norepinephrine, which enhances the inhibition of spinal cord neurons involved in pain perception [1].
Anesthetics. Topical lidocaine (5%) patches. It decreases small fiber nociceptive activity, and the patch itself serves as a protective barrier from the brush of clothing [2].
Capsaicin topical solution. In high concentrations it depletes substance P, a principal peptide neurotransmitter, causing a burning sensation and then anesthesia [3].
Anticonvulsants. Gabapentin: 600 mg/day orally. It binds to voltage dependent calcium channels located in the spinal cord. The action of gabapentin at these sites may inhibit the release of excitatory neurotransmitters and reduce glutamate availability at NMDA and non-NMDA receptors, thereby relieving pain [4].
References
  1. PARRUTI GIUSTINO, TONTODONATI , URSINI , POLILLI , VADINI , DI MASI . Post-herpetic neuralgia. IJGM [online] 2012 October [viewed 11 August 2014] Available from: doi:10.2147/IJGM.S10371
  2. SAMPATHKUMAR P, DRAGE LA, MARTIN DP. Herpes Zoster (Shingles) and Postherpetic Neuralgia Mayo Clin Proc [online] 2009 Mar, 84(3):274-280 [viewed 12 August 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2664599
  3. WOOD ALASTAIR J.J., KOST RHONDA G., STRAUS STEPHEN E.. Postherpetic Neuralgia — Pathogenesis, Treatment, and Prevention. N Engl J Med [online] 1996 July, 335(1):32-42 [viewed 11 August 2014] Available from: doi:10.1056/NEJM199607043350107
  4. BENNETT MICHAEL I, SIMPSON KAREN H. Gabapentin in the treatment of neuropathic pain. palliat med [online] 2004 January, 18(1):5-11 [viewed 13 August 2014] Available from: doi:10.1191/0269216304pm845ra

Management - Specific Treatments

Fact Explanation
Corticosteroids. Prednisolone: 5-60 mg/day. It reduces the inflammatory features of zoster and prevents the injury that follows it [1].
Antivirals. Famciclovir: 500 mg 8 hourly for 7 days (oral). By interrupting viral replication in the acute phase of herpes zoster, it may reduce damage to nerve fibers and subsequent onset of post zoster neuralgia [2].
Varicella zoster live attenuated vaccine. The vaccines can elicit a significant increase in cell-mediated immunity to varicella zoster and thereby provide protection against herpes zoster and postherpetic neuralgia [3].
References
  1. WOOD ALASTAIR J.J., KOST RHONDA G., STRAUS STEPHEN E.. Postherpetic Neuralgia — Pathogenesis, Treatment, and Prevention. N Engl J Med [online] 1996 July, 335(1):32-42 [viewed 11 August 2014] Available from: doi:10.1056/NEJM199607043350107
  2. PARRUTI GIUSTINO, TONTODONATI , URSINI , POLILLI , VADINI , DI MASI . Post-herpetic neuralgia. IJGM [online] 2012 October [viewed 11 August 2014] Available from: doi:10.2147/IJGM.S10371
  3. OXMAN M.N., LEVIN M.J., JOHNSON G.R., SCHMADER K.E., STRAUS S.E., GELB L.D., ARBEIT R.D., SIMBERKOFF M.S., GERSHON A.A., DAVIS L.E., WEINBERG A., BOARDMAN K.D., WILLIAMS H.M., ZHANG J. HONGYUAN, PEDUZZI P.N., BEISEL C.E., MORRISON V.A., GUATELLI J.C., BROOKS P.A., KAUFFMAN C.A., PACHUCKI C.T., NEUZIL K.M., BETTS R.F., WRIGHT P.F., GRIFFIN M.R., BRUNELL P., SOTO N.E., MARQUES A.R., KEAY S.K., GOODMAN R.P., COTTON D.J., GNANN J.W., LOUTIT J., HOLODNIY M., KEITEL W.A., CRAWFORD G.E., YEH S.-S., LOBO Z., TONEY J.F., GREENBERG R.N., KELLER P.M., HARBECKE R., HAYWARD A.R., IRWIN M.R., KYRIAKIDES T.C., CHAN C.Y., CHAN I.S.F., WANG W.W.B., ANNUNZIATO P.W., SILBER J.L.. A Vaccine to Prevent Herpes Zoster and Postherpetic Neuralgia in Older Adults. N Engl J Med [online] 2005 June, 352(22):2271-2284 [viewed 13 August 2014] Available from: doi:10.1056/NEJMoa051016