Myorhythmia: a widespread movement disorder. Clinicopathological correlations.

The clinical manifestations of 24 cases and the autopsy findings of 6 cases of extremity myorhythmia are presented. Extremity myorhythmia is that form of myorhythmia in which rhythmic alternating movements predominantly involve the limbs. The main difference between the tremor of extremity myorhythmia and the tremor of parkinsonism is the slower tremor rate, 2 to 3 cycles/s in myorhythmia and 4 to 6 cycles/s in parkinsonism. The mechanograms, except for the slower frequencies in myorhythmia, can be very similar, including sinusoidal oscillation patterns in both conditions. Myorhythmia may be defined as a coarse, alternating tremor, present at rest and usually during movement, which occurs at rates varying from 50 to 240 oscillations/min but mostly at either 120 to 140 or 160 to 180 cycles/min. The alternating movements may be intermittent or continuous or both types may be present in different body parts. When multiple parts are involved, synchronous or asynchronous movements are about equally common. Movements are usually relatively rhythmic and regular but may vary over periods of time in rate, rhythm or amplitude and rarely so, even over the course of a few hours and are absent during sleep. Movements may involve single limbs, several limbs or a combination of limbs plus face, palate, head, jaw, neck, tongue, eyes or trunk. The frequency of the movements in the 24 cases varied from 120 to 180 oscillations/min with two exceptions the slowest being 60 and the fastest 240, with most tending to cluster near either 120 or 180 cycles/min. The most common aetiologies were brainstem vascular disease and cerebellar degeneration secondary to chronic alcoholism-nutritional deficiency. The best prognosis occurred in the latter group. Clinicopathological correlations in our autopsy series indicate that myorhythmia of the limbs may occur ipsilateral to the dentate nucleus or superior cerebellar peduncle lesions or contralateral to inferior olive involvement. Unilateral lesions of the dentate nucleus may result in bilateral limb movements and bilateral dentate lesions may be associated with unilateral limb movements. The frequent involvement of the cerebellum and the substantia nigra suggests possible roles for the cerebellum and substantia nigra in the myorhythmia process.