What is the recommended evaluation and management approach for a patient with Becker's muscular dystrophy?

Evaluation and Management of Becker Muscular Dystrophy

All patients with Becker muscular dystrophy require immediate cardiac evaluation at diagnosis with physical examination, ECG, and echocardiography, followed by structured surveillance every 2 years until age 10, then annually thereafter, as cardiac complications are the primary driver of mortality in this population. 1

Initial Diagnostic Evaluation

Confirming the Diagnosis

• Obtain dystrophin genetic testing (deletion/duplication analysis followed by sequencing if negative) to identify the specific mutation, which is essential for genetic counseling and predicting phenotype severity 1, 2
• Measure serum creatine kinase, which will be markedly elevated (typically 5-100 times normal) and serves as a biomarker for ongoing muscle damage 1, 2
• Consider muscle biopsy only if genetic testing is inconclusive or to distinguish BMD from milder phenotypes, looking for reduced or abnormal dystrophin protein rather than complete absence 1, 2
• Perform baseline functional assessment including North Star Ambulatory Assessment (NSAA), timed rise from floor velocity, 4-stair climb velocity, and 10-meter walk test to establish trajectory and monitor progression 3

Cardiac Surveillance and Management

Initial Cardiac Assessment

• Perform comprehensive cardiac evaluation at diagnosis including physical examination, 12-lead ECG, and echocardiography regardless of age or symptoms 1
• Recognize that life-threatening ventricular arrhythmias can occur even without significant LV dysfunction in BMD, making rhythm monitoring critical 1
• Consider cardiac MRI with gadolinium as the preferred imaging modality over echocardiography for detecting early myocardial fibrosis and accurately measuring ventricular function, particularly in patients with chest wall deformities 1, 4

Ongoing Cardiac Monitoring Schedule

• Schedule cardiac evaluations every 2 years (physical exam, ECG, echocardiography) in asymptomatic patients under age 10 1
• Increase to annual cardiac evaluations starting at age 10, as cardiac complications accelerate with age 1
• Perform ambulatory ECG monitoring (Holter) every 1-3 years based on age, ejection fraction, and clinical assessment to detect arrhythmias, as LVEF <30-35% and age ≥17 years increase risk of nonsustained ventricular tachycardia 1
• Reevaluate at least annually if any LV dilation, dysfunction, or arrhythmia is detected, even if asymptomatic 1
• Increase monitoring frequency beyond annual for symptomatic patients, with specific intervals determined by clinical status and provider judgment 1

Cardiac Treatment Considerations

• Initiate ACE inhibitors and beta-blockers when cardiac dysfunction is detected, following standard heart failure management protocols 1, 2
• Recognize that cardiac decline is independent of skeletal muscle function, requiring vigilant monitoring even in patients with preserved ambulation 3

Neuromuscular Assessment and Monitoring

Functional Testing Schedule

• Assess muscle strength every 6 months in ambulatory patients using standardized measures including NSAA (most sensitive for clinical trials), rise from floor velocity (RFFv), and 4-stair climb velocity 1, 3
• Recognize that RFFv is the only outcome measure with high responsiveness at 3-year follow-up (SRM -0.91), while NSAA shows high responsiveness at 2 years when selecting patients with NSAA scores 10-32 at baseline 3
• Monitor for proximal muscle weakness progression, calf hypertrophy, and development of contractures at hip flexors, knee flexors, ankle plantar flexors, iliotibial band, and hamstrings 1, 2

Musculoskeletal Management

• Implement preventive physical therapy to maintain muscle extensibility and minimize contractures through passive stretching and range of motion exercises 1
• Prescribe low-intensity aerobic exercise (heart rate ≤65% of maximal oxygen uptake) on cycle ergometer or treadmill, as this improves physical performance and functional abilities without accelerating muscle damage 5
• Avoid eccentric or high-intensity training, which accelerates muscle degeneration in dystrophic muscle 5
• Consider orthopedic interventions for severe contractures or foot positioning issues affecting wheelchair use, though surgery is rarely necessary 1

Respiratory Management

• Perform pulmonary function testing every 6 months including forced vital capacity, maximum inspiratory pressure, maximum expiratory pressure, and peak cough flow 4, 2
• Recognize that upper limb and pulmonary function are typically preserved beyond loss of ambulation in BMD, unlike Duchenne muscular dystrophy 3
• Monitor for nocturnal hypoventilation and consider non-invasive ventilation if respiratory insufficiency develops 2

Pharmacological Considerations

Glucocorticoid Therapy

• Do not routinely prescribe glucocorticoids for BMD, as the evidence supporting their use is specific to Duchenne muscular dystrophy (prednisone 0.75 mg/kg/day or deflazacort 0.9 mg/kg/day) and has not been validated in the milder BMD phenotype 1, 6, 7
• Recognize that unlike DMD, BMD lacks proven pharmacological interventions for slowing muscle strength decline, making supportive care and cardiac management the cornerstones of treatment 7, 2

Multidisciplinary Care Coordination

• Establish care with a neuromuscular specialist who coordinates physical therapy (every 4 months), occupational therapy, cardiology, pulmonology, orthopedics, and psychosocial support 1, 4
• Schedule comprehensive clinic visits every 6 months with more frequent specialist assessments as indicated by disease progression 1
• Provide genetic counseling for female family members, as carriers require cardiac evaluation in the second to third decade of life with follow-up every 3-5 years 1

Critical Pitfalls to Avoid

• Never delay cardiac surveillance based on preserved skeletal muscle function, as cardiac complications develop independently and are the leading cause of mortality 6, 3
• Do not rely solely on echocardiography in patients with chest wall deformities or scoliosis, as technical limitations reduce interpretability; use cardiac MRI instead 1
• Avoid prescribing high-intensity or eccentric exercise, which accelerates muscle damage despite patients' desire to maintain strength 5
• Do not assume benign course based on the "milder" BMD label, as significant variability exists and some patients progress rapidly depending on mutation location (particularly those affecting nNOS binding site or with deletion of exons 45-47) 2, 3