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 re ported in the literature either as "jerky" tremor or myoclonus. We studied clinically and electrophysiologically these movements in 11 consecutive pat ients 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 invo lving just one or a few fingers, or more rarely the whole hand, were observ ed in nine patients when holding a posture or at the beginning of an action . Accelerometric recordings showed small-amplitude irregular oscillations w hich, 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 dur ation which were synchronous in antagonist muscles of the forearm and alter nated 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 electroe ncephalographic (EEG) and somatosensory evoked potentials to median nerve s timulation were normal. Back-averaging of the EEG activity time-locked to t he jerks was performed in two patients with no evidence of abnormal cortica l activity. Two patients had episodes of transient respiratory failure rela ted to pneumonia. This caused a long-lasting enhancement of the abnormal ha nd and finger movements, which became larger and more widespread, with feat ures of posthypoxic myoclonus. We conclude that the abnormal hand and finge r movements of patients with pMSA are st form of postural and action myoclo nus, and can be described as minipolymyoclonus.