The active von Frey filament test: A new technique to evaluate hand tactile sensation in continuous variable units

Abstract

The von Frey filament test (vF) is a mainstay of clinical examination. However, its results can be affected by touch speed and other potentially confounding factors. Moreover, the differences between two adjacent filament levels are too large to detect subtle changes. Active vF (AvF) was developed to induce in-depth sensory change. The present study hypothesized that AvF produces different patterns of fingertip sensation; consequently, it could be used as a new assessment tool for neural impairment. The aim of the study was to provide preliminary normative comparative vF and AvF data. This study prospectively examined 32 healthy participants, using AvF and vF. The index and the fifth finger volar pad were examined using AvF and vF, without visual stimulation. The correlation between AvF and vF measurements was evaluated. In addition, differences according to innervation zone, right versus left hand, and gender, and the correlation between AvF values and subjects’ age were analyzed. Mean AvF value was significantly higher and had greater variance than vF (111.3 46.9 vs. 24.1 9.8; P < 0.01). The Spearman correlation coefficient between AvF and vF was 0.341. Values were similar in the index and fifth fingers and right and left hands. However, values were significantly different between women and men. The correlation between age and AvF values was 0.259. AvF provided more precise values, with continuous units for tactile sensation, excluding tester-dependent factors. Furthermore, AvF and vF values may not be correlated.