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.