Argon laser induced cutaneous sensory and pain thresholds in post-herpetic neuralgia. Quantitative modulation by topical capsaicin.

Sensory and pain thresholds to cutaneous argon laser stimulation were determined in patients with post-herpetic neuralgia before and during treatment with topical capsaicin. Before treatment both thresholds were significantly elevated on the affected side compared to the contralateral normal area. After one week of capsaicin treatment both thresholds were significantly increased compared to the pre-treatment values, and the subjective pain relief, measured on a visual analogue scale (VAS) was 24%. More than 10% decrease in VAS pain score was obtained by 62.5% of the patients. Laser stimulations at levels at which the sensory and pain thresholds are reached were initially described as burning or stinging with pain projecting outside the stimulated area. This allodynia to laser stimulations changed during capsaicin treatment towards normal sensory and pain perception qualities. Both sensory and pain thresholds and the subjective pain score evaluated on a visual analogue scale were attenuated during the capsaicin treatment, suggesting a significant role of the cutaneous sensory and pain receptors in postherpetic neuralgia.