Positional vertigo and macroscopic downbeat positioning nystagmus in spinocerebellar ataxia type 6 (SCA6).

To investigate the frequency of positioning nystagmus in degenerative ataxic disorders, we examined downbeat positioning nystagmus (DPN) in 25 patients with spinocerebellar ataxia type 6 (SCA6) and 58 patients with other types of degenerative ataxia. DPN was observed in 21 of the 25 patients with SCA6 (84 %) versus only 3 of the 58 patients (5.2 %) with other types of degenerative ataxia, including multiple system atrophy, SCA1, SCA2, SCA3/Machado-Joseph disease, and non-SCA6 late-onset pure cerebellar ataxia. Our findings indicated that DPN is a distinct part of the clinical presentation of SCA6, showing that vestibular cerebellum is more affected in SCA6 than other types of degenerative ataxia.