Heller et al. 1 have reported recently a patient presenting a posterior fossa arachnoid cyst compressing the cerebellum in the midline. The patient exhibited an intermittent tremor in legs, which appeared after physical exertion. Tremor was provoked by asking the patient to run up and down a flight of stairs several times. The oscillations gradually abated after a few minutes. Postexertional surface electromyographic (EMG) re-cording showed irregular cocontracting bursts at a frequency of about 7 to 12 Hz. The authors suggest that tremor was induced by exercise possibly because of dynamic properties of the cyst, with intermittent disturbance of the olivary nuclei, the olivocerebellar projections, or the connections with the spinal cord. A psychogenic basis for the tremor could not be excluded. A marsupialization of the cyst was performed, followed by a improvement of the symptoms. This observation raises the possibility of an association between a midline posterior fossa malformation and fatigue-induced rhythmic contractions.
We report two patients presenting, respectively, a cerebellar hypoplasia and a Dandy-Walker-Blake malformation. In the two cases, exertion triggered a proximal tremor in upper limbs with a frequency of 3-4 Hz. The present observation illustrates that exercise-induced tremor may be found in other forms of posterior fossa malformations. To our knowledge, this is the first description of a low-frequency proximal tremor in upper limbs which is triggered by fatigue in patients with a cerebellar disorder. We suggest a pathophysiological hypothesis.