A novel method of diagnosing autonomic dysfunction in carpal tunnel syndrome: measuring skin capacitance.

Carpal Tunnel Syndrome (CTS) is normally diagnosed via its sensory and motor manifestations. The associated autonomic dysfunction has not been exploited to its full potential as a diagnostic tool due to the difficulties in quantifying it. We aim to demonstrate that autonomic dysfunction of CTS can be quantified by measuring skin capacitance. Fifty-one patients with clinical signs and electrophysiological evidence of CTS in 89 hands were recruited. Skin capacitance was measured using Corneometer CM825 (C&K Electronic, GmbH) from the palmar aspect of the distal phalanx of the index and little finger of the affected hand. Healthy gender- and age-matched individuals were recruited as controls. The mean ratio of hydration of the index to the little finger was 0.82. The mean difference was 10.98 arbitrary units. The control group consisted of 151 subjects (80 Male & 71 Female) and 302 hands with an average age of 40.1 years (18-81 years). The mean ratio of hydration of the index to the little finger was 0.87. The mean difference was 8.67 arbitrary units. The measurement ratios (index to little finger skin hydration) between the two groups was compared directly and gave a significant mean difference of 0.05 arbitrary units. Statistically significant differences in skin capacitance between CTS patients and controls have been demonstrated and quantified using a rapid and simple method. This can be used in clinic to reduce the reliance on Nerve Conduction Studies for diagnosing CTS.