Frequency-dependent conduction block in ulnar neuropathy localized to the elbow

Abstract

Objective To determine whether frequency-dependent conduction block (FDB) occurs in acute ulnar neuropathies localized to the elbow. Methods High-frequency nerve stimulation (30 Hz, 20 stimuli) was applied to the ulnar motor nerve above and below the elbow in controls (15) and in patients with short duration (between 2 and 16 weeks) ulnar neuropathy localized to the elbow (10) with evidence of moderate to severe conduction block and slowing. Results FDB was not observed in any of the 10 subjects tested. Three of these subjects were seen in follow-up; studies in two of these subjects, during the recovery period, did however demonstrate FDB with a similar pattern to that observed previously in CTS. Conclusions This study has demonstrated that the remaining unblocked ulnar motor fibers across the elbow in acute ulnar neuropathy with conduction block, do not demonstrate FDB in response to stimulation at 30 Hz. Significance These results suggest that FDB may not occur in the unblocked fibers in ulnar neuropathy despite evidence of conduction slowing. These results differ from previous observations in CTS and imply that demyelinating lesions (conduction block versus slowing) respond differently to high-frequency stimulation.