Conduction abnormalities detected by silent period testing

Cutaneous and mixed nerve silent periods (SPs) were analyzed in 2 patients with pure sensory neuropathy and in 5 healthy controls. In patients, sensory nerve action potentials (SNAPs) and somatosensory evoked potentials (SEPs) were absent, but digital and mixed nerve stimulation evoked complete SPs in voluntarily contracting thenar muscles. Marked differences in SP latencies were found between the patients, despite shared diagnoses and virtually identical nerve conduction studies. When compared with controls, SPs were normal in the first patient and markedly delayed in the second. Such findings suggest that SPs can identify conduction abnormalities not detected by routine studies. The pathologic correlate to these abnormalities remains uncertain, although electrophysiologic data suggest that the smaller, slower conducting delta fibers carry the impulses that generate these SPs.