RESUMEN
We report a case of unilateral tonic pupil in spinocerebellar ataxia without brainstem atrophy in a 42- year-old man. On neurological examination, he showed cerebellar symptoms and unilateral tonic pupil. Deep tendon reflexes were normal except for brisk patellar tendon reflexes. Brain MRI demonstrated cerebellar atrophy only. There was neither orthostatic hypotension nor bowel and bladder failure. The right pupil constricted from 5.0 mm to 1.7 mm 60 minutes after 0.125% pilocarpine administration, whereas the left pupil did not change, remaining at 3.7 mm. Although it is not proven that tonic pupil is causally related to spinocerebellar ataxia, physicians must remain aware of spinocerebellar ataxia as a disease that can demonstrate tonic pupil.