Bethlem Myopathy (Collagen VI-Related Dystrophies): A Retrospective Cohort Study on Musculoskeletal Pathologies and Clinical Course

Abstract

Background: Collagen VI-related myopathies with pathologic COL6A1, COL6A2, and COL6A3 variants manifest as a phenotypic continuum of rare disorders, including Bethlem myopathy (BM), characterized by early onset muscle weakness, proximal joint contractures, and distal joint laxity. Herein we discuss the concomitant orthopedic manifestations of BM, potential management strategies, and patient outcomes. Methods: An IRB-approved retrospective cohort study (n=23) from 2 pediatric institutions with a confirmed diagnosis of BM. Charts were reviewed for demographic data, age of disease presentation and diagnosis, COL6 genotype, diagnosis method, ambulation status, need for assistance, musculoskeletal abnormalities, other systemic comorbidities, advanced imaging and screening diagnostics, previous surgical interventions, and progression of the disease. Results: The mean age was 11.65 years (range 3 to 19 y). Mean age at initial presentation with symptoms was 4.18 years old, whereas diagnosis was delayed until 8.22 years old on average. Muscle weakness was the most common presenting symptom (65.2%), and 73.9% of patients required some use of assistive or mobility devices. Overall, 30.4% of patients were diagnosed with scoliosis; 57.1% required operative intervention for their scoliosis; 43.5% of patients had acetabular dysplasia; 10% required open reduction of a dislocated hip; 10% required closed reduction with hip spica application; 10% required bilateral periacetabular osteotomies for instability; 91.3% of patients developed foot and ankle deformities; 33.3% of patients underwent posteromedial-lateral equinovarus releases; 28.6% required an Achilles tendon lengthening, and 86.9% of patients had muscle tendon contractures, the most common locations being the ankle (55%) and elbow (40%). Conclusion: Although often less severe than other more common neuropathies and myopathies like Charcot-Marie-Tooth disease and Duchenne muscular dystrophy, BM does lead to progressive musculoskeletal deformity and disability. Its relative rarity makes it less familiar to providers and likely contributes to delays in diagnosis. Scoliosis, hip dysplasia, and equinus and varus ankle deformities are the most common musculoskeletal deformities. Physicians and surgeons should appropriately counsel patients and families about the clinical course of this disorder and the potential need for mobility assistance or surgical procedures. Level of Evidence: III, Prognostic. study.