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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Evidence of progressive muscle wasting and weakness

  • Dilated cardiomyopathy

  • Arrhythmias

  • Hypertrophic cardiomyopathy

  • Conduction abnormalities

  • Arrhythmias

  • Specific genetic diagnosis of a muscular dystrophy

GENERAL CONSIDERATIONS

  • Cardiac manifestations of inherited neuromuscular diseases can range from incidental findings on ECG to severe cardiomyopathy

  • Duchenne’s muscular dystrophy:

    • – The most common type (3/100,000 population) of inherited neuromuscular disease

    • – Mainly seen in males (X-linked recessive)

    • – Causes cardiomyopathy

    • – Usually diagnosed in childhood

  • Becker’s muscular dystrophy:

    • – Also sex linked, but with a delayed onset and slower progression than Duchenne’s

    • – The cardiomyopathy is often more severe

    • – Usually diagnosed in childhood

  • Myotonic dystrophy

    • – Autosomal dominant, trinucleotide expansion in the DMPK gene

    • – Associated with myotonia, cataracts, and diabetes

    • – Seen in 1:9000 population

    • – Usually manifests as conduction disturbances and atrial tachyarrhythmias

  • Emery-Dreifuss muscular dystrophy:

    • – An autosomal dominant, recessive, or X-linked disease due to mutations in 6 genes

    • – Usually causes conduction system disease, atrial standstill, and tachyarrhythmias, but can cause hypertrophic or dilated cardiomyopathy

  • Peroneal muscular atrophy (Charcot-Marie-Tooth syndrome):

    • – An autosomal dominant disease

    • – Can cause conduction abnormalities and cardiomyopathy

    • – Often causes atrial standstill

    • – Can cause brady-tachycardia syndromes

    • – Causes heart block in about 50% of cases

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Weakness of the affected skeletal muscles or dystonia

  • Dyspnea

  • Syncope

  • Palpitation

PHYSICAL EXAM FINDINGS

  • Muscle atrophy

  • Joint contractures

  • Signs of congestive heart failure

  • Murmur of mitral regurgitation

DIFFERENTIAL DIAGNOSIS

  • Cardiomyopathy from other causes with muscle atrophy and weakness from inactivity (cardiac cachexia)

  • Conduction, rhythm, and ECG abnormalities from other causes

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • Brain natriuretic peptides: elevated

  • Specific genetic analyses

  • Elevated creatine kinase and troponins

ELECTROCARDIOGRAPHY

  • Conduction abnormalities, especially atrioventricular block, distal block

  • Ventricular hypertrophy signs

  • Repolarization abnormalities

  • Arrhythmias

IMAGING STUDIES

  • Echocardiography may show dilated or hypertrophic cardiomyopathy, diastolic dysfunction, and mitral regurgitation by Doppler

  • MRI may show fatty deposits in the right ventricle of myotonic dystrophy patients

TREATMENT

CARDIOLOGY REFERRAL

  • Suspected cardiac disease

  • Syncope

HOSPITALIZATION CRITERIA

  • Syncope

  • Heart failure

MEDICATIONS

  • Therapy as indicated for heart failure

  • Antiarrhythmic drug therapy as appropriate

THERAPEUTIC PROCEDURES

  • Pacemaker or implantable cardioverter-defibrillator as indicated

SURGERY

  • Cardiac transplantation in selected cases

MONITORING

  • ECG monitoring in hospital as appropriate

DIET AND ACTIVITY

  • Low-sodium diet if heart failure

ONGOING MANAGEMENT

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