The diagnostic value of water immersion skin wrinkling and Neuropads in small fiber neuropathy.

Objective: To investigate the diagnostic yield of two simple tests for small fiber neuropathy (SFN): Neuropads® and water immersion skin wrinkling (WISW).

Methods: We studied 35 patients clinically diagnosed with SFN and 61 age- and sex-matched healthy controls. Wrinkling was judged as absent (abnormal), or present (normal) after immersion of the hands for 30 min. Neuropads are plasters impregnated with cobalt blue that are applied with to the soles of the feet. These remain blue when feet are dry (abnormal) or turn pink when there is some moisture (normal).

Results: The sensitivity of the Neuropad was 29% and its specificity 93%. The sensitivity of WISW was 66% and its specificity 70%. Regarding abnormality of at least one test to define the combination as abnormal yielded a sensitivity of 71% and specificity 67%. When both tests had to be abnormal to judge the combination abnormal, sensitivity was 23% and specificity 97%.

Conclusions: The Neuropad has a high specificity, so an abnormal result can be used to confirm SFN. WISW has a moderate sensitivity and specificity. Combining these two tests can be helpful: when both tests are abnormal the diagnosis SFN is highly likely.

Significance: The Neuropad and WISW can be helpful in daily practice by supporting the diagnosis SFN.