The realistic yield of lower leg SNAP amplitudes and SRAR in the routine evaluation of chronic axonal polyneuropathies

Objective :To assess the realistic yield of lower leg sensory nerve action potential amplitudes (SNAP) and the sural/radial nerve amplitude ratio (SRAR) in the routine evaluation of suspected distal axonal polyneuropathy. Methods :Investigated were 721 people. In 393 referents without and 328 patients with chronic distal symmetrical polyneuropathy the SRAR, sural, superficial peroneal and dorsal sural SNAP were determined. Results :The dorsal sural SNAP could not be elicited in 26 % of referents. Axonal polyneuropathy was confirmed by an abnormally low value of the sural or superficial peroneal SNAP or SRAR in 70 % of patients, and most often (68 %) by an absent sural or superficial peroneal SNAP. In 9 % of patients there was a normal sural but abnormal superficial peroneal SNAP, and 11 % had an abnormal sural but normal superficial peroneal SNAP. ROC curve analysis demonstrated equal accuracy of the sural and superficial peroneal SNAP. Conclusions :To confirm distal axonal polyneuropathy in routine clinical practice the sural and superficial peroneal SNAP had equal and complementary yield, whereas the SRAR and dorsal sural SNAP had limited additional yield.