Correlation between the size of the compound muscle and sensory nerve action potentials recorded from the foot in distal axonopathy.

Nerve conduction study was performed on 71 diabetic patients with distal sensorimotor axonopathy. Of 76 lower limbs studied, 46.1% showed no recordable sural compound sensory nerve action potential (CSNAP), and 55.3% no superficial peroneal CSNAP. Only 2.6% revealed no recordable compound muscle action potential (CMAP) from the abductor hallucis (AH) muscle, and 9.2% showed no obtainable CMAP from the extensor digitorum brevis (EDB) muscle. There were fairly good positive correlations between the amplitudes of the sural CSNAPs and AH CMAPs (r = 0.66), and between the superficial peroneal CSNAP and EDB CMAP amplitudes (r = 0.63). There were no instances in which a CSNAP could be obtained from the sural or superficial peroneal sensory nerve, but a CMAP could not be recorded from the AH or EDB muscle. If the CMAP amplitudes of the AH and EDB muscles were reduced to less than 0.3 mV, usually a CSNAP could longer be recorded from the sural and superficial peroneal sensory nerves. The size of the CSNAP is a more sensitive measure compared to the CMAP in revealing the presence of distal sensorimotor axonopathy.