Cardiomyopathy in muscular dystrophy

Extract

A 43-year old man with muscular dystrophy was referred for cardiovascular evaluation. He had been confined to a wheelchair since being diagnosed in his early 20s. His cardiovascular examination was unremarkable. The electrocardiogram showed sinus rhythm with dominant R-waves in the early precordial leads (Figure 1A). Echocardiography and cardiac magnetic resonance (CMR) cine imaging were unremarkable with a normal ejection fraction of 55%. However, CMR late gadolinium enhancement (LGE) imaging demonstrated striking epicardial hyperenhancement of the lateral wall (Figure 1B, arrows), consistent with myocardial fibrosis from underlying dystrophin deficient cardiomyopathy.

Dystrophinopathies are a group of neuromuscular diseases resulting from mutations in the structural cytoskeletal gene - dystrophin¹. They include Duchenne and Becker muscular dystrophy. Mutations leading to the absence of functional dystrophin cause Duchenne muscular dystrophy, whereas mutations resulting in reduced amounts or shortened dystrophin protein cause Becker muscular dystrophy,¹ Cardiomyopathies are a common manifestation of these disorders and contribute significantly to morbidity and mortality. Death can occur due to heart failure, heart block or ventricular arrhythmias. Early detection and initiation of heart failure therapy may delay progression of the cardiomyopathy.² The bright regions seen on LGE imaging represent focal myocardial fibrosis.³ This patient’s late presentation and milder disease is clinically consistent with Becker muscular dystrophy rather than Duchenne muscular dystrophy.¹ This was confirmed by genetic testing which showed a deletion mutation in the dystrophin gene encompassing exons 52–54, associated with reduced amounts of functional dystrophin.