Reproducibility of a heteronymous monosynaptic reflex in biceps brachii

The present study provides normal data for a new technique to assess conduction across the C5/C6 segments by recording a heteronymous monosynaptic reflex response from the contracting biceps brachii in response to stimulation of the median nerve in the cubital fossa. The reflex responses were reproducible and symmetrical, with a mean latency of 14.8 msec (S.D. 1.4 msec) and an absolute side-to-side differences of 0.5 msec (S.D. 0.29 msec). Latency was significantly correlated with both age and height, and multiple regression analysis provided the following equation: latency (msec) = 0.091 x height (in cm) + 0.036 x age (years) - 1.988. Amplitudes had wide scatter (22-365 microV on the right side) and positive skew. An amplitude less than 40% of that for the other side would be outside the 90th percentile. Five cases are described to illustrate the potential clinical utility of this test. However, whether this reflex is of diagnostic value can be answered only by a prospective study comparing it with other routine investigations.