Diagnosis and management of postherpetic neuralgia.

Risk factors for postherpetic neuralgia (PHN) include: increasing age; a prodrome of pain before rash onset; the degree of spread of the rash, particularly if it extends beyond a single dermatome; and severity of pain during the acute attack. Forty per cent of patients over 50 and 75% of those over 75 develop PHN following resolution of the rash. Patients develop persistent pain classified as PHN 120 days following rash onset. It can be either constant or paroxysmal and is commonly described as burning, stabbing or itching and located in the same dermatomal distribution as the shingles rash. Pain can lead to sleep disturbance, anorexia, reduced socialisation and reactive depression. Paracetamol should be tried initially for mild to moderate pain, either alone or in combination with codeine but there is no evidence to support the use of NSAIDs. Compared with other antidepressants, tricyclic antidepressants are the most likely to confer benefit in neuropathic pain. In frail elderly patients nortriptyline appears to be tolerated best. Both gabapentin and pregabalin can reduce pain and improve sleep patterns in patients with PHN. Patients with severe pain or those whose condition is affecting their daily activities and function should be referred to a specialist in pain management.