The nomenclature and classification of sporadic spinocerebellar degeneration

Spinocerebellar degeneration (SCD) is a neurodegenerative disease characterized by progressive cerebellar ataxia. SCD has a wide range of clinical, pathological, and genetic features, including whether the disease is sporadic or hereditary, and whether it manifests as purely cerebellar or affects multiple systems. Therefore, the classification of SCD has been complicated and has changed over time. Recent advances in genetic testing have shed light on the classification of hereditary SCD. In contrast, the classification of sporadic SCD remains chaotic and there exist nomenclature discrepancies in sporadic SCD between Japanese and English literature. Sporadic SCD is usually divided into multiple system atrophy and cortical cerebellar atrophy in Japanese literature, but the latter nomenclature seems to be uncommon in English literature. The aim of this review is to reconsider the nomenclature and classification of sporadic SCD. At this time, sporadic adult-onset ataxia of unknown etiology is an acceptable term to describe a case of sporadic SCD that does not fit the multiple system atrophy classification.