Overview
Definition:
Duchenne muscular dystrophy (DMD) is a severe, X-linked recessive genetic disorder characterized by progressive muscle degeneration and weakness
Cardiomyopathy is a common and serious complication in individuals with DMD, affecting a significant proportion of patients and contributing to morbidity and mortality
It typically involves dilated cardiomyopathy with progressive fibrosis.
Epidemiology:
DMD affects approximately 1 in 3,500 to 6,000 live male births worldwide
Cardiomyopathy is almost universal in older males with DMD, with clinical manifestations often appearing in late childhood or adolescence, though subclinical changes can be present earlier
The incidence of severe cardiac dysfunction increases with age.
Clinical Significance:
Cardiac involvement in DMD significantly impacts prognosis and quality of life
Early detection and proactive management of cardiomyopathy are crucial to prevent heart failure, arrhythmias, and sudden cardiac death
Understanding the surveillance strategies is vital for pediatricians and cardiologists managing these complex patients, and a core competency for DNB and NEET SS preparation.
Clinical Presentation
Symptoms:
Patients may be asymptomatic in early stages
Symptoms can include fatigue
Shortness of breath, especially with exertion
Palpitations
Exercise intolerance
Swelling in the legs or abdomen (edema)
Chest pain (less common initially)
These often overlap with general DMD symptoms, making cardiac monitoring essential.
Signs:
Physical examination may reveal signs of heart failure such as tachycardia
Gallop rhythm (S3, S4)
Jugular venous distension
Peripheral edema
Hepatomegaly
Arrhythmias on auscultation
However, early stages may have normal findings.
Diagnostic Criteria:
There are no universally defined specific diagnostic criteria for DMD cardiomyopathy separate from the diagnosis of DMD itself
However, the diagnosis is typically established based on a combination of clinical findings consistent with dilated cardiomyopathy in a patient with confirmed DMD, supported by echocardiographic evidence of left ventricular dysfunction (e.g., reduced ejection fraction, ventricular dilation) and/or ECG abnormalities
International guidelines provide recommendations for screening and monitoring.
Diagnostic Approach
History Taking:
Detailed family history of neuromuscular or cardiac disease
Symptom onset and progression
Assessment for shortness of breath, exercise intolerance, palpitations, and edema
Review of previous cardiac assessments
Inquiry about adherence to prescribed medications.
Physical Examination:
Systematic cardiovascular examination including heart rate, rhythm, presence of murmurs, gallops, rubs, and signs of fluid overload (jugular venous distension, peripheral edema, pulmonary rales)
Assessment of respiratory status.
Investigations:
Electrocardiogram (ECG): Often shows sinus tachycardia, tall R waves in V1, deep S waves in V5-V6 (left ventricular hypertrophy pattern), ST-T wave abnormalities, and arrhythmias (e.g., supraventricular tachycardia, premature ventricular contractions)
Echocardiography: The cornerstone of surveillance, assessing left ventricular dimensions, wall thickness, systolic function (ejection fraction, fractional shortening), diastolic function, and presence of valvular regurgitation
Cardiac Magnetic Resonance Imaging (CMR): Can provide detailed myocardial characterization, including fibrosis detection and quantification, and assessment of ventricular volumes and function, particularly useful when echocardiography is suboptimal
Cardiac biomarkers (e.g., troponin, BNP): May be elevated in decompensated heart failure but are not primary surveillance tools
Genetic testing: Confirms the diagnosis of DMD by identifying mutations in the DMD gene.
Differential Diagnosis:
Other causes of dilated cardiomyopathy in children: viral myocarditis
Idiopathic dilated cardiomyopathy
Other muscular dystrophies (e.g., Becker muscular dystrophy, limb-girdle muscular dystrophies)
Congenital heart disease
Anthracycline-induced cardiotoxicity.
Management
Initial Management:
For asymptomatic patients, management is primarily preventative, focusing on ACE inhibitors and beta-blockers to delay disease progression
For symptomatic patients, treatment aims to manage heart failure and arrhythmias.
Medical Management:
Angiotensin-converting enzyme (ACE) inhibitors (e.g., Ramipril, Enalapril): Standard of care even in asymptomatic patients to delay onset and progression of cardiomyopathy
Doses are typically started low and titrated up, based on age and weight, e.g., Ramipril 0.03-0.07 mg/kg/day
Beta-blockers (e.g., Carvedilol, Bisoprolol): Also used in asymptomatic patients to slow progression and improve cardiac function
Carvedilol is often preferred due to its alpha and beta-blocking effects
Doses are titrated cautiously, e.g., Carvedilol 0.1-0.7 mg/kg/dose twice daily
Diuretics (e.g., Furosemide): Used for symptom relief in heart failure, typically for fluid overload
Aldosterone antagonists (e.g., Spironolactone): May be considered in advanced heart failure
Digoxin: For rate control in atrial arrhythmias or for inotropic support in severe heart failure
Anti-arrhythmic medications: Based on the type and severity of detected arrhythmias.
Surgical Management:
Heart transplantation is an option for select patients with end-stage heart failure refractory to medical management, but it is complex due to systemic weakness and potential respiratory compromise.
Supportive Care:
Regular cardiac monitoring as per guidelines
Nutritional support to maintain adequate weight and muscle mass
Pulmonary hygiene
Physical therapy to maintain function
Psychological support for patient and family.
Complications
Early Complications:
Acute heart failure exacerbations
Life-threatening arrhythmias (e.g., ventricular tachycardia, ventricular fibrillation)
Pericarditis.
Late Complications:
Progressive dilated cardiomyopathy
Congestive heart failure
Pulmonary hypertension
Systemic thromboembolism
Sudden cardiac death.
Prevention Strategies:
Early initiation of ACE inhibitors and beta-blockers in all DMD patients, regardless of cardiac symptoms
Strict adherence to prescribed medications
Regular cardiac screening and surveillance
Prompt management of arrhythmias and heart failure symptoms
Avoidance of cardiotoxic agents where possible.
Prognosis
Factors Affecting Prognosis:
Age of onset of cardiomyopathy
Severity of cardiac dysfunction (ejection fraction, ventricular dilation)
Presence and type of arrhythmias
Response to medical therapy
Extent of respiratory and skeletal muscle involvement
Adherence to treatment.
Outcomes:
With current management strategies, median survival has improved significantly
Cardiac complications remain a major cause of mortality, but effective surveillance and treatment can delay progression and improve quality of life
Patients can often live into their late twenties or thirties, with cardiac care being a key determinant.
Follow Up:
Regular cardiac assessments are essential throughout the lifespan of individuals with DMD
Guidelines typically recommend: Echocardiography and ECG every 1-2 years starting from age 5-10 years, or earlier if symptomatic
More frequent monitoring may be required based on findings or disease progression
Annual specialist review by a pediatric cardiologist experienced in neuromuscular disorders is advisable.
Key Points
Exam Focus:
DMD cardiomyopathy is a progressive dilated cardiomyopathy
ACE inhibitors and beta-blockers are indicated even in asymptomatic patients
Echocardiography is the primary surveillance tool
ECG changes include tall R in V1 and deep S in V5-V6
Cardiac complications are a leading cause of mortality.
Clinical Pearls:
Start cardiac prophylaxis (ACE-I and beta-blockers) at diagnosis or by age 10 at the latest, even without symptoms
Do not wait for symptoms to initiate management
Consider CMR for better fibrosis assessment if echo is equivocal
Monitor for arrhythmias and heart failure symptoms diligently.
Common Mistakes:
Delaying cardiac evaluation and prophylaxis until symptoms appear
Inadequate dosing or monitoring of ACE inhibitors and beta-blockers
Underestimating the risk of arrhythmias
Neglecting regular cardiac screening in asymptomatic individuals.