Common peroneal mononeuropathy: a clinical and electrophysiologic study of 116 lesions.

We analyzed the clinical and electromyographic (EMG) findings of 116 common peroneal mononeuropathies in 103 patients (13 with bilateral lesions). Prior to the EMG examination, the diagnosis was not clinically suspected or seriously considered in 44% of the lesions. Sensory manifestations were common (79%) but pain was rare (16.5%). The onset was acute in 57 patients, gradual in 35, and indeterminate in 11. Of the 116 lesions, 64 were solely axonal loss in type, 23 manifested as conduction block, presumably secondary to focal demyelination, and 29 were a mixture of the two. Contrary to common belief, the pathophysiology was predominantly axonal loss regardless of etiology, including those that developed perioperatively. The peroneal motor nerve conduction study, recording tibialis anterior muscle, was the single most important electrophysiologic study; it localized all 52 lesions causing conduction block at the fibular head. In contrast, peroneal motor conduction velocity along the knee-to-fibular head segment was seldom abnormal, with slowing in only five of the 52 cases.