Cardiovascular magnetic resonance imaging in the diagnosis of cardiac involvement in patients with Becker-Kiener muscular dystrophy

Purpose: Muscular dystrophy type Becker-Kiener (BMD) represents an X-linked disease due to mutations in the dystrophin gene. Apart from skeletal myopathy, cardiac involvement with the development of dilated cardiomyopathy (DCM) has been described, mainly based on echocardiographic studies. DCM is an important cause of mortality in these patients. The course of DCM can potentially be alleviated by timely onset of adequate medication. However, the underlying pathophysiology of cardiac involvement in muscular dystrophy is still to be explored and echocardiography has method-inherited limitations. Therefore, cardiovascular magnetic resonance imaging (CMR) represents a promising non-invasive tool for accurate cardiac evaluation in these patients.

Methods: In a prospective two-center-study, 14 patients with BMD underwent cardiac evaluation. Work-up included physical examination, echocardiography and CMR. A 16-segment model was applied for evaluation of regional wall motion abnormalities (rWMA) and quantification of a global systolic wall motion score index (GWMS). The CMR study included late gadolinium enhancement (LGE) imaging with quantification of myocardial fibrosis.

Results: In 7 of 14 patients, cardiac involvement has already been documented by previous echocardiography. Within this study, pathologic echocardiographic results (defined as left ventricular ejection fraction (LVEF) <55% and/or rWMA) were found in 8 of 14 patients with all of them demonstrating reduced LVEF and rWMA. By contrast, CMR revealed pathological findings (defined as LVEF <60% and/or rWMA and/or presence of LGE) in 12 of 14 patients (p=0.040 compared to echocardiography) with 10 of them having reduced LVEF (p=0.16) and 9 demonstrating rWMA (p=0.43). Myocardial fibrosis was present in 11 of 14 patients as assessed by LGE imaging with a mean myocardial fibrosis extent of 11.7±10.0%. Correlation analyses revealed a substantial association between increased myocardial fibrosis and decreased LVEF (r²=0.46; p=0.008). Nine patients were actually in need of medical therapy based on clinical symptoms and CMR results.

Conclusions: Cardiac involvement in patients with muscular dystrophy is underdiagnosed by echocardiographic methods. For a sensitive diagnosis of cardiac involvement in patients with BMD, comprehensive CMR studies including LGE imaging are required. The prognostic value of non-invasive cardiac fibrosis imaging in patients with BMD has to be explored in future studies.