Median-radial latency difference: its use in screening for carpal tunnel syndrome in twenty patients with demyelinating peripheral neuropathy.

The median-radian latency difference (MRLD) has been advocated as a screen for mild carpal tunnel syndrome (CTS); however, its validity in the face of even mild peripheral neuropathy is questionable. The MRLD of 20 consecutive individual referred with electrodiagnostic evidence of demyelinating peripheral neuropathy was obtained using standard techniques. The MRLD was statistically prolonged in 85% of the subjects without corroborating evidence of CTS (p < .05). Additionally, statistically significant (p < .05) differences were noted between the percentage of prolonged latencies of the radial sensory (50%) and the median sensory (100%) and all sensory nerves (97%). This investigation suggests that superficial radial nerve involvement in demyelinating peripheral neuropathy occurs later than other sensory nerves. This data indicates that though the MRLD may serve as a sensitive screening method for CTS, it has a low specificity therefore, a more extensive evaluation for mild peripheral neuropathy is always indicated.