A 16-year-old male patient with known Becker's muscular dystrophy (BMD), with deletion of exon 48–49, was noted to have recent deterioration in already limited functional capacity. The transthoracic echocardiogram revealed moderately impaired left ventricular systolic function, with ejection fraction of 44% (Figure 1A), and preserved relaxation (Figure 1B). A cardiovascular magnetic resonance (CMR) study was performed and confirmed high-normal indexed left ventricular volumes with moderately reduced global ejection fraction (48%). No active inflammation was seen. Late gadolinium-enhanced images showed typical subepicardial fibrosis of the lateral and inferior wall from base to mid-ventricular level (Figure 1C and D).

Figure 1.

(A) Transthoracic echocardiogram in parasternal view depicting a dilated left ventricle with moderately reduced ejection fraction. (B) Tissue Doppler imaging of lateral mitral inflow velocities, with an E/e′ ratio of 5.3, suggestive of normal filling pressures. (C and D) Cardiovascular magnetic resonance images with late gadolinium enhancement showing typical subepicardial inferolateral fibrosis (white arrows), also involving the mid-septum (dashed arrow), consistent with Becker's cardiomyopathy.

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BMD is an X-linked inherited progressive myopathic disorder caused by mutations in the dystrophin gene; the dystrophin protein plays an essential role in signal pathways and stabilization of the cardiomyocyte cell membrane. It is characterized by proximal skeletal muscle weakness and wasting. Cardiac muscle can be affected, with degeneration of fibers, replacement fibrosis and fatty infiltration. The pathophysiology is not entirely understood; it is postulated that diffuse myocardial metabolic abnormalities lead to fibrosis, starting, as in this patient, in the subepicardium of the inferolateral wall, due to greater mechanical stress in this region. Progressive cardiomyopathy, often subclinical in the early stages, is a major cause of morbidity and mortality. Advanced echocardiographic assessment of diastolic function and tissue characterization by CMR enable early detection of cardiac involvement and timely initiation of heart failure treatment to prevent ventricular remodeling.