THE EFFECT OF ETHANOL ON ALCOHOL RESPONSIVE ESSENTIAL TREMOR - A POSITRON EMISSION TOMOGRAPHY STUDY

We used (H2O)-O-15 positron emission tomography (PET) to investigate t he effect of ethyl alcohol on regional cerebral blood flow in 6 patien ts with alcohol-responsive essential tremor and 6 age-matched control subjects. The patients were scanned while at rest and during involunta ry postural tremor of the extended right arm. Normal control subjects were scanned at rest and during passive wrist oscillation of the right arm at tremor frequency. Regional cerebral blood how associated with these conditions was measured before and after oral administration of 2 to 3 units of alcohol. The mean blood alcohol level was 35.3 +/- 20. 0 mg/dl in the patient group and caused marked suppression of tremor; it was 33.9 +/- 12.9 mg/dl in the control group. Similar to previous P ET studies on essential tremor patients, tremor compared with rest was associated with bilateral cerebellar activation including the cerebel lar vermis. This pattern of activation differed from passive wrist osc illation where ipsilateral cerebellar activation was observed. Ethanol ingestion led to bilateral decreases of cerebellar blood flow in both tremor patients and normal subjects, and this was associated with sup pression of tremor in the patients. Alcohol-associated increases of re gional cerebral blood flow were observed in the inferior olivary nucle i in the patients but not in the control subjects. We conclude that al cohol-induced suppression of essential tremor is mediated via a reduct ion of cerebellar synaptic overactivity resulting in increased afferen t input to the inferior olivary nuclei.