Clinical Reasoning: A 60-Year-Old Man With Ataxia, Chorea, and Mild Cognitive Impairment.

We describe the case of a 60-year-old man with a 16-year history of gait imbalance and a 15-year history of forgetfulness. The insidious onset and slow progression suggested that the disease was degenerative. Neurologic examination revealed cerebellar ataxia, chorea, and mild cognitive impairment. Brain MRI revealed prominent cerebellum atrophy and diffuse atrophy in the brainstem and cerebrum. Based on neurologic manifestations, an additional patient interview and skin examination were conducted. Photosensitivity and freckling in exposed areas, which the patient did not recognize as disease symptoms, were observed. Based on acute and chronic photosensitivity and DNA repair test results, a final diagnosis was made. In patients with cerebellar ataxia, chorea, and cognitive dysfunction of unknown etiology, clinicians should explore patients' history of photosensitivity and carefully examine the skin.