Quantitation of axon loss and conduction block in acute radial nerve palsies.

Eleven acute radial nerve palsies were examined between 3 days and 14 weeks following the onset of the neuropathy. Our objective was to quantify the relative extent of axon loss and conduction block in radial motor fibers supplying the extensor and abductor pollicis longus (EPL/APL) muscles. In 10 of 11 cases, conduction block exceeded axon loss. Maximum motor and sensory conduction velocities were normal distal to the spiral groove, suggesting that the larger myelinated fibers were not selectively involved in this acute neuropathy. The localization of the conduction block and slowing was, in every case, across the spiral groove. This method provides a relatively simple way of assessing the approximate contributions of axon loss and conduction block, and fits well with the early and usually complete clinical recovery in these cases.