Predicting and preventing post-herpetic neuralgia: are current risk factors useful in clinical practice?

Post-herpetic neuralgia (PHN) following acute herpes zoster remains a significant cause of neuropathic pain especially in the elderly. Early treatment of the zoster rash with antiviral agents, such as aciclovir remains one of the few measures proven to reduce the incidence and duration of PHN albeit only in a subset of patients. It is therefore crucial that the physician who first sees a case of zoster identifies those patients who are most likely to develop long-term pain and treats them accordingly. In particular, prodrugs such as famciclovir and valaciclvoir may be more beneficial in reducing PHN than the shorter acting aciclovir, but can be more expensive. Measures that could be used to predict patients likely to develop PHN would also facilitate the evaluation of early use of antiepileptic, anti-inflammatory and analgesic agents in the prevention of PHN. In a prospective study of 280 herpes zoster (HZ) cases seen by the general practitioner (GP) we evaluated the predictive value of five clinical factors identified in clinical trials as associated with a higher likelihood of PHN. A visual analogue score (VAS) over 5 and/or age over 50 correctly identified all subjects with PHN at 3 and 6 months, respectively. However, the specificity of this prediction was low because as many as 81% and 85% of those aged over 50 recovered within 3 and 6 months, respectively. Better methods are needed to identify patients over 50 at most risk of PHN that enable GPs to better allocate their resources with respect to HZ treatment.