Postural and action myoclonus in patients with parkinsonian type multiple system atrophy.

Patients with a parkinsonian syndrome and features of multisystem atrophy (pMSA) may exhibit abnormal movements of the hands and fingers, which are reported in the literature either as "jerky" tremor or myoclonus. We studied clinically and electrophysiologically these movements in 11 consecutive patients with pMSA. No abnormal movements were observed when the patients were at complete rest, except for a characteristic parkinsonian "pill-rolling" tremor in one patient. Abnormal small-amplitude, nonrhythmic movements involving just one or a few fingers, or more rarely the whole hand, were observed in nine patients when holding a posture or at the beginning of an action. Accelerometric recordings showed small-amplitude irregular oscillations which, contrary to those of patients with tremor, had no predominant peak in the Fast Fourier frequency spectrum analysis. Electromyographic recordings in the forearm and hand muscles showed brief jerks of less than 100 ms duration which were synchronous in antagonist muscles of the forearm and alternated with brief periods of silence. Electrical stimulation of the digital nerves evoked consistent reflex responses in the wrist flexor and extensor muscles at a latency of 55.3+/-4.1 ms (range, 50-63 ms). Routine electroencephalographic (EEG) and somatosensory evoked potentials to median nerve stimulation were normal. Back-averaging of the EEG activity time-locked to the jerks was performed in two patients with no evidence of abnormal cortical activity. Two patients had episodes of transient respiratory failure related to pneumonia. This caused a long-lasting enhancement of the abnormal hand and finger movements, which became larger and more widespread, with features of posthypoxic myoclonus. We conclude that the abnormal hand and finger movements of patients with pMSA are a form of postural and action myoclonus, and can be described as mini-polymyoclonus.