Tremor-spectrum in spinocerebellar ataxia type 3.

Spinocerebellar ataxia type 3 (SCA3) can be present with a combination of cerebellar, neuropathic, pyramidal, or extrapyramidal symptoms. Tremor is a classical but not frequent manifestation of SCA3 and there is a lack of detailed knowledge regarding its origin. To study the clinical and electrophysiological characteristics of tremor in SCA3 patients, the authors conducted a case series of 72 SCA3 patients. Clinical characteristics of tremor and associated signs, response to treatments, follow-up, and genetic results were collected. Electrophysiological study including polymyographic recording was possible in 4/6 patients and DaTSCAN in 2/6. The authors also performed a systematic review of SCA3 cases with tremor (n = 36) reported previously in the literature. We identified two different tremor-types in 6/72 patients with SCA3 mutations, a "fast" (6.5-8 Hz) action, postural or tremor in orthostatism (initial symptom), which became slower over time with associated parkinsonism with a follow-up of 10 years and a "slow" rest, action and intention tremor (3-4 Hz) with distal and proximal component (including axial tremor in orthostatism). Total improvement of limbs and tremor in orthostatism was obtained with levodopa with occurrence of fluctuations/dyskinesia. Partial benefit was observed when additional signs were present (myoclunus/dystonia). The differences in tremor subtypes in SCA3 may be related to various combinations of mild to severe dysfunctions of the cerebello-thalamo-cortical loop and the nigro-striatal dopaminergic pathway.