Limb myorhythmia in association with hypertrophy of the inferior olive: report of two cases.

We report on 2 patients who uncommonly developed isolated limb myorhythmia in association with inferior olive hypertrophy (IOH) after an acute stroke in the brain stem. A slow tremor presented in the proximal upper limbs predominantly when at rest. It was aggravated by outstretched arms and by active hand movements. The surface electromyogram (EMG) recorded simultaneous activities over the agonist and antagonist muscles with a rate of 3.5 Hz and 2.5 Hz in 2 patients respectively. In the first patient, bilateral limb myorhythmia presented 12 months after the brain stem stroke, and both inferior olives were hypertrophic. In the second patient, unilateral limb myorhythmia developed in the left hand 7 months after right pontine hemorrhage, and only the right inferior olive was hypertrophic. These findings indicate that limb myorhythmia commencing after brain stem insult is anatomically and temporally related to hypertrophy of the contralateral inferior olive. Based on our 2 patients and previously reported cases, we propose that a possible causal relationship exists between limb myorhythmia and contralateral IOH, although its pathophysiological mechanisms remain to be established. We suggest that, similar to palatal myoclonus, isolated limb myorhythmia is within the clinical spectrum of IOH.