Comprehensive Assessment of Cardiac Involvement in Muscular Dystrophies by Cardiac MR Imaging

Neuromuscular diseases and their cardiac manifestations under the spectrum of cardiovascular imaging

Neuromuscular diseases (NMDs) include a broad spectrum of disorders that affect motor unit in every possible site, extending from the cell body of peripheral nerves to the muscle. The different lesion sites make this group of inherited disorders difficult to diagnose. Many NMDs, especially those involving skeletal muscles, can present significant cardiovascular complications, ranging from rhythm disturbances to the development of dilated or hypertrophic cardiomyopathy. Heart disease represents a major cause of morbidity and mortality among NMD patients, underlining the vital need for further familiarization with the pathogenesis and assessment of cardiac involvement. Cardiovascular imaging is the cornerstone for the evaluation of heart disorders in NMDs, with conventional echocardiography still offering a portable, affordable, and easily accessible solution. Meanwhile, newer echocardiographic techniques such as speckle tracking imaging in combination with cardiac magnetic resonance add new insights into further substrate characterization. The purpose of this review is to offer a brief presentation of the main NMDs and their cardiovascular complications, as well as the presentation of data that highlight the importance of cardiovascular imaging in early diagnosis, monitoring, and prognosis of these patients. Lastly, the authors provide a simple guide about which clinical features, imaging findings, and follow-up plan to adopt in each myopathic disorder.

Cardiac MR Imaging of Muscular Dystrophies

Muscular dystrophies (MDs) are a group of inherited disorders caused by mutations that interfere with muscular structure, contraction, or relaxation. As the cardiac sarcomeric unit shares multiple proteins with the skeletal muscle unit, the heart is affected in several MDs, sometimes without apparent musculoskeletal involvement. Early detection of MD-related cardiomyopathy is crucial as timely initiation of cardioprotective therapy can slow adverse cardiac remodeling. Although transthoracic echocardiography is widely used for the evaluation of cardiac morphology and function, it has limitations in terms of reproducibility and image quality. The need for an optimal acoustic window may be particularly challenging to obtain in patients with MDs given their body habitus and position. Cardiac magnetic resonance (CMR) imaging has emerged as a useful tool in the evaluation of patients with MDs. Its superb tissue characterization capability through late gadolinium enhancement, T1 mapping, extracellular volume fraction quantification, and edema imaging detects early cardiac involvement, even when echocardiography and electrocardiogram are unremarkable. MDs that frequently present with cardiac involvement include Duchenne MD, Becker MD, Emery Dreifuss MD, Limb-Girdle MDs, and myotonic dystrophy. The purpose of this review article is to briefly describe the pathophysiology of these entities, discuss their clinical presentation and expected evolution, explain the role of CMR in the diagnosis and follow-up of these patients, and portray the different CMR findings present in MD patients.

Duchenne muscular dystrophy: an overview to the cardiologist

INTRODUCTION

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy in children, affecting approximately one in 3,500-5,000 liveborn boys. The main signs and symptoms include gait disturbances beginning in early childhood, with later onset of respiratory and cardiac function disorders, both directly affecting the prognosis.

AREAS COVERED

The recent improvement of mechanical ventilation increased the mean DMD survival age; however, there has been little progress in the treatment and prevention of cardiac complications, which currently predominantly impact survival. Cardiological evaluation with imaging methods, such as echocardiography and magnetic resonance imaging, can improve the understanding and detect changes in cardiac function early.

EXPERT OPINION

Close monitoring by the cardiologists and early treatment, with adequate heart disease stratification, may be the key to prolong the lives of these patients until more promising therapies are available and can predict DMD prognosis and progression more accurately. The objective of this brief review is to update the cardiologists by highlighting the most relevant aspects of treatment and follow-up, in a practical and concise way.

MiRNAs, Myostatin, and Muscle MRI Imaging as Biomarkers of Clinical Features in Becker Muscular Dystrophy

Becker muscular dystrophy (BMD) is an X-linked recessive disorder caused by dystrophin gene mutations. The phenotype and evolution of this muscle disorder are extremely clinical variable. In the last years, circulating biomarkers have acquired remarkable importance in their use as noninvasive biological indicators of prognosis and in monitoring muscle disease progression, especially when associated to muscle MRI imaging. We investigated the levels of circulating microRNAs (myo-miRNAs and inflammatory miRNAs) and of the proteins follistatin (FSTN) and myostatin (GDF-8) and compared results with clinical and radiological imaging data. In eight BMD patients, including two cases with evolving lower extremity weakness treated with deflazacort, we evaluated the expression level of 4 myo-miRNAs (miR-1, miR-206, miR-133a, and miR-133b), 3 inflammatory miRNAs (miR-146b, miR-155, and miR-221), FSTN, and GDF-8 proteins. In the two treated cases, there was pronounced posterior thigh and leg fibrofatty replacement assessed by muscle MRI by Mercuri score. The muscle-specific miR-206 was increased in all patients, and inflammatory miR-221 and miR-146b were variably elevated. A significant difference in myostatin expression was observed between steroid-treated and untreated patients. This study suggests that microRNAs and myostatin protein levels could be used to better understand the progression and management of the disease.