Validation of a simplified provocation instrument for diagnosis and threshold testing of symptomatic dermographism

Symptomatic dermographism is a common urticarial condition, which requires determination of provocation thresholds to confirm diagnosis and allow physicians to individualize management and therapy for optimal control of symptoms. To determine provocation thresholds, we have developed a provocation test device, the FricTest(®) 4.0. This simple and inexpensive device, which is stroked across the skin to produce a response, consists of a flat plastic comb with four round-ended plastic pins, 3 mm in diameter, and of differing lengths.

To validate the FricTest(®) 4.0 by comparison with FricTest 3.0 in determining provocation thresholds in symptomatic dermographism,

Dermal provocation with the FricTest 4.0 and FricTest 3.0 was performed in parallel on the volar forearm of 30 patients with symptomatic dermographism and 30 healthy controls. The widths of the resulting weals were measured, and weals with a width of ≥ 3 mm were considered positive. Accompanying pruritus was assessed using a 10-point verbal rating scale.

All 30 patients with symptomatic dermographism, but none of the healthy volunteers, showed positive responses to provocation with the strongest trigger strength, showing that FricTest(®) 4.0 has 100% sensitivity and specificity for diagnosing symptomatic dermographism. Quantitatively, both devices were similar in the number of patients who responded positively to different pin lengths. Results for pruritus were also similar with both instruments.

The FricTest 4.0 is a simple and inexpensive instrument for determining provocation thresholds in patients with symptomatic dermographism. It should find a place in both routine clinical investigation and in therapeutic trials.