Postherpetic neuralgia and its treatment: a retrospective survey of 191 patients.

One hundred and ninety-one patients with postherpetic neuralgia (PHN) in whom treatment was begun 3 or more months after acute herpes zoster (HZ) were retrospectively considered. Relieved (> or = 75% fall in visual analogue score for worst pain within last 24 hr) and unrelieved groups were subdivided into those who had and those who had not received antiviral treatment for their acute shingles. More than 90% of all patients experienced allodynia with a clinically evident sensory deficit for temperature and/or pinprick sensation. The probability of relief is worst in patients with PHN of the isolated ophthalmic nerve and of the brachial plexus, and best when involving the jaw, neck, and trunk. The presence (90%) or absence of allodynia has no predictive significance; but the small number of patients without allodynia or sensory deficit (all of whom had had antiviral treatment for their acute shingles) all improved. The probability of pain relief was found to correlate very strongly with the brevity of the interval between rash onset and commencement of treatment with an adrenergically active antidepressant. Further, time to relief in patients treated with an antidepressant starting at the same interval after HZ is significantly shorter in patients who received acyclovir for their original HZ. With the possible exception of dextroamphetamine added to the antidepressant, other treatments (particularly analgesics, anticonvulsants, and sympathetic blockade) were found to be without value in most cases. Thirty percent of patients who recover from PHN and have had their original shingles treated with acyclovir subsequently suffer from severe itching. It is recommended that elderly patients be given low-dose antidepressant on diagnosis of shingles, and asked to report back in 6 weeks. If they are pain-free at this interval, low-dose antidepressant should be continued for another month or so and then stopped. If, however, pain is present at 6 weeks, the dose of antidepressant should be increased and the patient reviewed every 2 months.