Cap myopathy

Cap myopathy (also known as cap disease) is an extremely rare congenital myopathy, a subtype of the broader group of nemaline myopathies, classified under ICD-10 code G71.2. It is named after the characteristic 'cap-like' structures found beneath the sarcolemma (muscle cell membrane) on muscle biopsy. These cap structures consist of disorganized myofibrils and thickened Z-disc material that form peripheral, well-demarcated regions within muscle fibers. The disease primarily affects the skeletal muscular system, leading to progressive or nonprogressive muscle weakness. Clinical features typically include generalized muscle weakness and hypotonia, which may be present from birth or early childhood. Patients often exhibit facial weakness, a long face (elongated facies), high-arched palate, and skeletal abnormalities such as scoliosis, scapular winging, and joint contractures. Respiratory insufficiency is a significant concern and can be life-threatening, particularly in severe neonatal presentations. Dysphagia (difficulty swallowing) and feeding difficulties may also occur. The severity of cap myopathy is highly variable, ranging from mild weakness with near-normal function to severe neonatal forms with respiratory failure. Cap myopathy has been associated with mutations in several genes, including TPM2 (beta-tropomyosin), TPM3 (gamma-tropomyosin), and ACTA1 (skeletal muscle alpha-actin). Most reported cases are sporadic, though autosomal dominant inheritance has been documented in some families. There is currently no cure or disease-specific treatment for cap myopathy. Management is supportive and multidisciplinary, including physical therapy to maintain mobility, respiratory support (including non-invasive ventilation when needed), orthopedic interventions for scoliosis and contractures, and nutritional support for those with feeding difficulties. Regular monitoring of respiratory function is essential.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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