The wide clinical spectrum and nigrostriatal dopaminergic damage in spinocerebellar ataxia type 6

Spinocerebellar ataxia type 6 (SCA6) manifests a wide spectrum of non-cerebellar system involvements. The objective of this study was to examine the presence of nigrostriatal dopaminergic system derangement in SCA6. Eight patients with SCA6 who underwent a regular follow-up for at least 2 years participated in this study. A detailed neurological examination was performed and striatal dopamine transporter (DAT) was evaluated using [ 99m Tc]–TRODAT-1 SPECT. The main clinical feature of SCA6 was cerebellar ataxia with impaired eye movements. However, a wide spectrum of non-cerebellar system involvements, such as autonomic dysfunction, and pyramidal and extrapyramidal signs, was also observed. Two patients had bradykinesia. l-dopa was tried in one patient without benefit. Of the two patients with bradykinesia, DAT density was reduced to the Parkinson9s disease (PD) range with a rostrocaudal gradient typical of PD in one patient (CAG repeats 13/22) and was mildly decreased in the other patient (12/25). Of the four patients without extrapyramidal signs, three (12/22, 11/25, 17/22) showed mild to severe reduction of DAT density and one (13/22) had a normal density. This study shows that SCA6 has a varying degree of nigrostriatal dopaminergic derangement. Two patients manifested mild bradykinesia, emphasising the need to screen for SCA6, even in patients with progressive ataxia and parkinsonism. Further histopathological studies would be helpful to determine the nigrostriatal dopaminergic damage in SCA6.