Abnormal unloading reflex in a patient with infarction of the medial lemniscus.

The unloading reflex was measured in the intrinsic muscles of the hand. By removing various fractions of the load on the muscles, we determined the size of the electromyographic response as a function of the change in the external force. This technique was applied to both hands of a patient with a pontine lesion who had impaired position sense in the left hand. The response to fractional unloading was significantly smaller in the left hand, an asymmetry not found in control subjects. The results suggest (1) that the unloading reflex is mediated, at least in part, by suprasegmental pathways, and (2) that the fractional unloading technique can reveal abnormalities not found by conventional methods.