Hemichorea as the sole clinical manifestation of spinocerebellar ataxia type 8: a case report.

Background: Spinocerebellar ataxia type 8 (SCA8) is a rare neurodegenerative disease that is caused by CAG/CTG repeat expansion in the overlapping ATXN8 and ATXN8OS genes and basically entails slowly progressive cerebellar dysfunction with resultant dysarthria, limb incoordination, and gait instability. Moreover, patients with SCA8 may also exhibit pyramidal and extrapyramidal signs, cognitive decline, and involuntary movements. Although SCA8 is an autosomal dominant inheritance disorder, it sometimes seems to be sporadic because of reduced penetrance. Due to the wide variety of neurological findings and seemingly unclear inheritance pattern, the diagnosis of SCA8 can be difficult in the absence of cerebellar signs or family history.

Case presentation: A 62-year-old woman presented with involuntary movements in her right limbs that occurred intermittently for two weeks. Her medical and medication history was unremarkable and she had a paternal grandmother who was diagnosed with Parkinson's disease. Neurological examination revealed right-sided hemichorea without other abnormalities. Head magnetic resonance imaging (MRI) did not reveal acute ischemic or hemorrhagic lesions; instead, it displayed mild cerebellar atrophy. In addition, dopamine transporter-single photon emission computed tomography (DAT-SPECT) detected bilaterally decreased striatal tracer uptake. Although she had no relatives with similar symptoms or SCA, a set of genetic molecular tests for SCA was conducted because she had mild cerebellar atrophy found on MRI. It detected CTA/CTG repeat expansion in the ATXN8OS gene (18/125 repeats; normal range: 15-50). She was diagnosed with SCA8, which was considered the cause for her hemichorea. Oral haloperidol was initiated as symptomatic treatment and it largely resolved her hemichorea.

Conclusions: We should remember that patients with SCA8 can present with hemichorea as the sole clinical manifestation. Moreover, DAT-SPECT may detect their nigrostriatal hypofunction even if they do not have clinically apparent parkinsonism.