Background: Bethlem myopathy is considered a relatively mild neuromuscular disorder without significant cardiac and respiratory involvement. Objective: To investigate cardiac and respiratory involvement in Bethlem myopathy. Design: Cross-sectional study. Setting: University hospitals. Patients: Fifty patients with Bethlem myopathy from 26 families. Interventions: Cardiac examinations, including electrocardiography and echocardiography (n = 37) and pulmonary investigations (n = 43). Holter monitoring was performed in 16 patients. Main Outcome Measures: Cardiac and respiratory abnormalities. Results: Several cardiac abnormalities were found that were considered unrelated to the muscular disorder. Seven (16%) of 43 patients had a forced vital capacity less than 70% of the predicted value. One of 2 patients with a forced vital capacity less than 50% was also receiving respiratory support. All patients with compromised respiratory function were still ambulatory, and we found no significant correlation between the severity of arm weakness and the severity of respiratory muscle involvement. Conclusions: There is no evidence of cardiac involvement in Bethlem myopathy. Respiratory failure is part of the clinical spectrum and can occur in ambulatory patients.
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