Inherited Neuromuscular Disease and the Heart

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