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

Autophagic vacuolar myopathy involving the phenotype of spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3) is a form of autosomal dominant cerebellar ataxia with a wide range of clinical manifestations, including ataxia and pyramidal and extrapyramidal signs. A few SCA3 patients have been noticed to be predisposed to the development of inclusion body myositis. It is still unknown whether muscle can be primarily involved in the pathogenesis of SCA3. This study reported an SCA3 family in which the index patient initially presented with parkinsonism, sensory ataxia, and distal myopathy but the absence of cerebellar and pyramidal symptoms. The clinical and electrophysiological studies implied a possible combination of distal myopathy and sensory-motor neuropathy or neuronopathy. MRI muscle showed selective fat infiltration and absence of denervated edema-like changes, indicating the distal muscle weakness had a myopathic origin. Muscle pathology showed the myopathic involvement, besides neurogenic involvement, characterized by chronic myopathic changes with multiple autophagic vacuoles. Genetic screening revealed expanded CAG of 61 repeats in the ATXN3 gene, which showed co-segregation in the family. Besides the neurogenic origin, the myopathic origin may be partly attributed to the limb weakness of SCA3 patients, which expands the spectrum of the clinical manifestation of SCA3.

What is in the Myopathy Literature?

This update begins with muscle manifestations of coronavirus 2019. They may include myalgias and elevations in serum creatine kinase. It is unknown whether there is direct muscle invasion and how often the critically ill have muscle sequelae. Regarding autoimmune myopathies, a retrospective study of statin-induced necrotizing myopathy is covered. A relatively large proportion of patients had normal strength at presentation. Examples of dermatomyositis associated with immune checkpoint inhibitors are provided including one with cytokine storm. A report of juvenile dermatomyositis with severe abdominal complications is noteworthy. Two articles address unusual associations with inclusion body myositis, namely, spinocerebellar ataxias and granuloma myositis. In the category of muscular dystrophies, a relatively large single center study of the outcome of scapulothoracic arthrodesis for facioscapulohumeral muscular dystrophy is discussed and a article on anoctaminopathies with pauci- or asymptomatic hyperCKemia.