Aftersensations in experimental and clinical hypersensitivity

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Abstract
This study examined aftersensations after repetitive pinprick stimulation in nerve injury patients with allodynia and in capsaicin sensitized skin in control subjects. Forty-one patients and 12 male control subjects were stimulated repetitively with a computer-driven von Frey hair in sensitized skin and in contralateral normal skin at 0.2 and 2.0Hz. Pain during and after stimulation was scored on an electronic visual analogue scale and sampled on a computer. Maximum evoked pain, time to pain onset, duration of pain and duration of aftersensations were calculated from stored data. Aftersensations were significantly more frequent in sensitized skin than in contralateral normal skin in both control subjects and patients. Pain was evoked more frequently and maximum evoked pain score was significantly higher in sensitized skin compared to contralateral normal skin in both groups. Furthermore, evoked pain score was frequency dependent with a significantly higher pain score at 2.0 than at 0.2Hz. There was a significant positive correlation between maximum evoked pain scores and duration of aftersensations both in patients and control subjects. No difference was observed in maximum pain score, time to pain onset and duration of aftersensations between the groups. Findings suggest that aftersensations and evoked pain are mediated by a common mechanism, which most likely is central. The clinical manifestation of aftersensations can be mimicked in an experimental pain model so aftersensations may be another useful parameter in assessment of central sensitization.