P78 Getting to the core of the matter: cores as a common muscle pathology finding in the collagen VI-related myopathies

Abstract

Abstract The interpretation of muscle biopsies in the collagen VI-related myopathies can be challenging, given that specific structural abnormalities are not present, the pathology is often not overtly dystrophic and the immunohistochemical studies of collagen VI can be difficult to interpret when basal lamina defects are subtle. The muscle histopathology finding of cores is classically associated with the core myopathies but can be seen in other conditions including collagen VI-related myopathies. A comprehensive retrospective review of muscle biopsies was performed in 15 collagen VI-related myopathy patients, comparing histological findings to those seen in muscle biopsies of 14 RYR1 or SEPN1-related core myopathy patients. Clinical notes were reviewed (ARF), and only cases with molecularly confirmed diagnoses were included. Biopsy review was independently performed (RP), blinded to the biopsy findings originally reported (CS). Cores and/or minicores were present in the muscle biopsies of 12/15 (80%) of molecularly confirmed collagen VI-related myopathy patients studied. Both large and small neonatal myosin positive fibres were present in collagen VI-myopathy patients in contrast to the presence of only tiny neonatal myosin positive fibres seen in RYR1-related core myopathy patients. We conclude that cores are a common muscle histopathology finding in molecularly confirmed collagen VI-related myopathy patients. It is, therefore, important to include collagen VI-related myopathies in the differential diagnosis when cores are seen on muscle biopsy, especially given their clinical overlap with congenital myopathies and the invariable and often insidious decline in respiratory function in patients with this congenital muscular dystrophy subtype which must be addressed. These histopathology findings in conjunction with clinical and muscle imaging findings may assist in refining the challenging diagnostic pathway for the collagen VI-related myopathies.