Spinocerebellar Ataxia Type 3 Accompanied by Amyotrophic Lateral Sclerosis: A Case Report and Comprehensive Literature Review.

Spinocerebellar ataxia type 3 (SCA3) is a hereditary neurodegenerative disorder characterized by cerebellar ataxia, whereas amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease. We herein report a 62-year-old man with genetically confirmed SCA3 who subsequently developed rapidly progressive asymmetric muscle weakness, atrophy, and fasciculations. Clinical features, including preserved tendon reflexes and widespread denervation observed on electromyography, support the diagnosis of concomitant sporadic ALS. Our literature review revealed only a few similar cases, suggesting the under-recognition of this rare combination. This case underscores the importance of considering coexisting ALS in patients with SCA3 to enable a timely diagnosis and management.