Inclusion body myositis in patients with spinocerebellar ataxia types 3 and 6.

Objectives: To describe the combination of spinocerebellar ataxia (SCA) types 3 and 6 and sporadic inclusion body myositis (IBM).

Methods: A description of five patients with SCA type 3 and 6 who were diagnosed with IBM. We explore possible mechanisms explaining the coexistence of both diseases.

Results: The patients with SCA-3 (n=4) and SCA-6 (n=1) developed asymmetric muscle weakness in a pattern suggestive of IBM in the course of their disease. Based on findings of neurological examination and additional investigations (muscle ultrasound, muscle biopsy), the diagnosis of IBM was made in all patients.

Conclusion: We report on five patients with concomitant SCA and IBM. Our cases may merely illustrate coincidental co-occurrence of IBM and SCA-3/SCA-6. However, the presence of SCA mutations could predispose to the development of IBM in some SCA patients, or, the presence of toxic aggregates and malfunctioning of cellular quality control processes in both diseases could indicate a convergence of disease mechanisms.