[Periodic alternating nystagmus in spinocerebellar ataxia type 6 (SCA 6)].

We report a 61-year-old man with SCA 6 manifesting periodic alternating nystagmus (PAN). He first noted transient, recurrent episodes of "dizziness" at age 56. The symptom appeared several times a day, lasting for 3 years. At age 59, unsteady gait developed insidiously. On neurological examination, he showed limb and truncal ataxia, marked gaze nystagmus, and positional nystagmus. Thereafter, his ataxia became worse and PAN developed. Brain MRI showed pathologic atrophy which was confined to the cerebellum. PAN was rarely reported in spinocerebellar ataxia, being not described in SCA 6. The episodic "dizziness" at the initial stage has not gained much attention. Our observation indicates that the initial manifestation of SCA 6 overlaps with that of episodic ataxia type 2, an allelic disorder of SCA 6. PAN and fluctuating symptoms, as seen in our patient, must be carefully examined to see whether or not they can be parts of clinical presentations in SCA 6.