Serial electrodiagnostic studies in acute partial conduction block from cyclist's palsy

To date, there is minimal literature in following resolution of partial conduction block (PCB) in compression neuropathy. We investigated a case of cyclist's palsy with PCB from compression using serial nerve conduction studies to monitor recovery.

Clinical recovery was monitored concomitant with compound muscle action potential (CMAP) amplitudes that were recorded from 3 ulnar-innervated muscles (first dorsal interosseous [FDI] 6 days post-onset, palmar interosseus [PI] 16 days post-onset, and abductor digiti minimi [ADM]) in both limbs. Sensory nerve conduction studies and needle electromyography were also performed.

PCB was demonstrated in the FDI and PI with recordings done proximal and distal to the site of injury. Recovery in the FDI and PI occurred between week 2 and 3 post-onset but continued to improve until about 14 wk post-onset when the CMAP values on the affected side approximated the contralateral side. Sensory conduction studies were normal and symmetric. Needle EMG at 21 days post-injury showed no active denervation and a reduced number of normal-appearing motor unit potentials firing >16 Hz that reverted to a normal pattern on final study at 99 days post-onset.

This study shows how rapidly PCB may initially resolve although full recovery takes longer. Criteria for defining PCB may be misleading when doing nerve conductions and comparing only the evoked responses below and above the block. To fully characterize PCB, it is important to optimize the position of the active recording electrode (E1) as well as compare results with the unaffected side.