High-frequency synchronous bursts firing associated with asynchronous midbrain tremor.

We describe a patient who developed a tremor following a hemorrhage in the brainstem due to an arteriovenous malformation. Brain MRI disclosed lesions in the mesencephalon and a marked enlargement of the fourth ventricle. In addition to an asynchronous midbrain tremor in the upper limbs (frequency o f 4.5-6 Hz), she exhibited short periods of 15-16 Hz synchronous tremor whe n upper limbs were maintained outstretched. These high-frequency bursts wer e absent in the lower limbs. The synchronous firing was relieved by hyperfl exion of the wrists. We believe that the high-frequency discharges were due to the disruption of cerebellar pathways. Indeed, a similar tremor has bee n reported in patients presenting a symptomatic postural tremor associated with disruption of cerebellar afferences and/or efferences. We suggest that the disappearance of the high-frequency tremor following the hyperflexion of the wrist might be due to a resetting of the peripheral receptors (muscl e spindles) activity, in agreement with the hypothesis that the stretch ref lexes associated with postural tasks are impaired in patients exhibiting ce rebellar ataxia.