Isolated tremor and disruption of the nigrostriatal dopaminergic system: an 18F-dopa PET study.

We measured striatal 18F-dopa influx constants (Ki) for 20 patients with isolated, predominantly postural, tremor (eight familial, 12 sporadic) and 11 with predominantly rest tremor. Results were compared with 30 controls and 16 Parkinson's disease (PD) patients. The eight familial essential tremor (ET) patients had normal striatal 18F-dopa uptake. Two of the 12 sporadic postural tremor patients had subnormal putamen 18F-dopa Ki, one (who later became akinetic) falling in the PD range. The mean putamen 18F-dopa uptake of the 11 rest tremor patients was reduced to PD levels (51% of normal). Our findings argue against an association between ET and PD, but support the existence of a "benign" tremulous variant of PD. The presence of low-amplitude rest tremor, cogwheel rigidity, reduced arm swing, and short tremor duration was not a useful predictor of nigral dysfunction in patients with postural tremor. In contrast, patients with predominantly rest tremor, particularly with onset in the leg, consistently showed reduced putamen 18F-dopa uptake.