Initially with pure parkinsonian phenotype of spinocerebellar ataxia type 3: A rare case report and literature review

Background: Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is an autosomal dominant genetic disease with substantial heterogeneity in clinical manifestations. It typically starts with ataxia and can be divided into five subtypes. The fourth subtype of SCA3 is characterized by parkinsonian and peripheral neuropathy. However, this phenotype is rare, and it tends to be easily misdiagnosed as Parkinson's disease. Materials and methods We report a 51-year-old female patient who initially presented with pure parkinsonian symptoms at the age of 30. She responded well to levodopa treatment and had a diagnosis of Parkinson's disease for almost 20 years. Ataxia symptoms, symptom fluctuations and dyskinesia occurred in the late stage of the disease. A literature review was included to summarize the clinical features of the fourth subtype of SCA3 (type IV SCA3) and its relevant pathogenesis. Results Type IV SCA3 with 66 CAG repeats was diagnosed by genetic testing. It is initially characterized by a pure parkinsonian phenotype indistinguishable from PD, short CAG repeat expansions, and a good response to levodopa. Conclusion Type IV SCA3 should be considered when diagnosing Parkinson's disease, especially in those with a family history. More research is needed to detect the pathogenesis of the parkinsonism phenotype in type IV SCA3.