Introduction to Postherpetic Neuralgia – A possible complication of Shingles
Shingles is a disease caused by the varicella-zoster virus (VZV). While it is related to chickenpox, the two entities are distinctly different. VZV causes both chickenpox and shingles. After an initial chickenpox infection, VZV stays dormant in the body and may become re-activated years later to manifest as shingles. Postherpetic neuralgia is a complication of shingles. Postherpetic neuralgia is a neuropathic pain syndrome in which the pain persists for months to years even after the resolution of the initial shingles infection.
Clinical Presentation of Shingles
Within 2 to 3 days of onset, the typical symptoms of shingles begin to occur. The tingling sensations evolve to become a more severe stinging or burning pain. This is followed by slightly red patches of skin with small bumps overlying it. In hours, these bumps progress into blisters which become itchy. This stage usually lasts for about 5 days. The blisters eventually dry up in anywhere from 2 to 10 days and leave behind yellow scabs. The skin symptoms take a total of 2 to 4 weeks to resolve. Shingles most commonly affects the chest wall or back, but can also occur anywhere else on the body, such as the face, arms or head. Rarely, shingles can re-activate in nerves within the eyes or ears.
In postherpetic neuralgia, the pain arises from the same regions which were affected by shingles. Patients typically describe 3 types of pain – constant (burning/aching/throbbing), intermittent (stabbing/shooting/electric shock-like) and pain that is brought on by a non painful stimulus (hyperalgesia). These pain-related symptoms persist for at least 3 months even after shingles has resolved.
The two most important diagnostic criteria in postherpetic neuralgia are a recent history of shingles, as well as the nature of the pain (at least one of the 3 types mentioned above). Unfortunately, there are no other reliable laboratory or imaging studies that can reliably diagnose postherpetic neuralgia.
Postherpetic neuralgia is notoriously challenging to manage. However, despite the fact that no single best treatment has been identified, there are a plethora of analgesic options to consider in ameliorating the pain associated with it. Tricyclic antidepressants, gabapentin and pregabalin are three such options which could be considered by a pain specialist. The safety, performance and tolerability of these drugs must be carefully weighed and discussed with the patient. Topical lidocaine patches, opioids and capsaicin patches are useful adjunct medications that could also be tried for refractory cases of postherpetic neuralgia. In view of this, the pain specialist has a significant role in evaluating for drug-drug interactions and balancing the expected side-effects with the intended goal of providing pain relief.