Dynamic mechanical allodynia: on the relationship between temporo-spatial stimulus parameters and evoked pain in patients with peripheral neuropathy.

The relationship between temporo-spatial stimulus parameters and evoked pain intensity as well as duration was examined in patients with peripheral neuropathy and brush-evoked allodynia, i.e. dynamic mechanical allodynia. Brush-evoked allodynia was induced in the innervation territory of the lesioned nervous structure in 18 patients by lightly stroking different distances of the skin (20, 40, 60 mm) two or four times with brushes of different widths (4, 8, 16 mm). Pain intensity and duration of brush-evoked allodynia was recorded using a computerized visual analogue scale. The total brush-evoked pain intensity, including painful aftersensation was calculated as the area under the curve. Following each stimulus, the patients selected pain descriptors from a validated instrument. Significantly increased total brush-evoked pain intensity was demonstrated with increased brushing length and number of strokes (P<0.001), but not while altering brush width. Lack of influence of brush width was further underlined by the finding that activation of equivalent areas (e.g. 160 mm2) resulted in higher total brush-evoked pain intensity if brushing the skin with a thin brush (4 mm) over a longer distance (40 mm) than a thick brush (8 mm) over a shorter distance (20 mm). Significantly increased duration of aftersensation was demonstrated only following increased brushing length (P<0.008). The most commonly used sensory-discriminative pain descriptors were pricking, burning and sore and for the affective descriptors, annoying and troublesome. This is the first study demonstrating a relationship between evoked pain and some temporo-spatial stimulus parameters during brush-evoked allodynia.