Absence of long latency reflexes to imposed finger displacements in patients with Huntington's disease.

Long latency reflexes in the electromyogram (EMG) of the first dorsal interosseus muscle were elicited by short finger displacements under isometric conditions. In all healthy subjects tested the spinal response was followed by a second involuntary component. Patients with Huntington's disease lacked the late EMG response almost completely, but exhibited a spinal component indistinguishable from that of the control group. A spinal mechanism responsible for this result is unlikely, since double stretches evoked two distinct EMG responses in these patients. Moreover, drastically reduced cortical somatosensory evoked potentials in all patients support the notion that the second EMG response seen in our motor paradigm is of supraspinal origin.