Isolated tremor and disruption of the nigrostriatal dopaminergic system

TLDR

The study measured striatal ¹⁸F‑dopa influx constants in 20 isolated postural tremor patients (8 familial, 12 sporadic) and 11 rest tremor patients, comparing the results to 30 controls and 16 Parkinson’s disease patients. Familial essential tremor patients had normal striatal ¹⁸F‑dopa uptake, whereas sporadic postural and rest tremor patients exhibited reduced uptake—rest tremor patients reaching Parkinson’s disease levels—supporting that isolated tremor is not associated with Parkinson’s disease but may represent a benign tremulous variant, and that low‑amplitude rest tremor or other clinical signs poorly predict nigral dysfunction.

Abstract

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 Parkinson9s 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.