How to measure and reduce the burden of zoster-associated pain.

Several parameters of shingles' pain can be measured and each provides meaningful information. Generally, the more comprehensive the assessment the better, but there are significant difficulties in measuring the duration of post-herpetic neuralgia (PHN). Patients with herpes zoster usually feel pain as a continuum and, although acute pain and PHN have different qualities and pathophysiologies, we lack the sophistication to determine when PHN commences. Use of an arbitrarily defined starting point is meaningless for the patient and may introduce statistical bias (particularly if acute pain and PHN are divided by the point of rash healing). Thus, measurement of the pain as a continuum ('zoster-associated pain') is advocated. We also need to decide what degree of pain intensity is meaningful and whether complete cessation of pain or loss of pain (or only 'moderate/severe' pain) for a finite period is a better assessment. This approach to pain measurement was recently adopted in a meta-analysis of the placebo-controlled trials of oral aciclovir in herpes zoster. When 'time to complete cessation of all pain' was assessed, the hazard ratio was 2.13 in favour of aciclovir, with a 95% confidence interval (CI) of 1.42 to 3.19. For 'time to complete cessation of moderate/severe pain' the hazard ratio was 1.46 (95% CI; 1.11, 1.93); for 'time to first pain-free period' it was 1.31 (95% CI; 1.08, 1.60). These results indicate that aciclovir significantly speeds pain resolution in shingles.