What are the high-yield points for Step 2 regarding diagnosis and management of Becker Muscular Dystrophy (BMD) in a male patient with a family history of BMD?

High-Yield Step 2 Points for Becker Muscular Dystrophy (BMD)

Diagnosis and Initial Workup

The most critical diagnostic test for BMD is serum creatine kinase (CK), which is markedly elevated (typically >1000 U/L), followed by genetic testing of the dystrophin gene for confirmation. 1

Key Diagnostic Features

• BMD is an X-linked disorder caused by in-frame deletions in the dystrophin gene that produce partially functional dystrophin protein (versus DMD's out-of-frame deletions causing complete absence) 1
• Presentation is typically milder and later than DMD, with patients maintaining ambulation longer and not requiring glucocorticoid therapy 1
• Family history may reveal affected males on the maternal side, though approximately one-third are new mutations 1
• Physical exam shows proximal muscle weakness and calf pseudohypertrophy 1
• Skeletal muscle severity does NOT correlate with cardiac involvement severity—this dissociation is critical 1

Initial Laboratory Testing

• Serum CK is the first-line screening test and can be ordered in primary care 1
• If CK elevated, confirm diagnosis with dystrophin gene sequencing 1
• Genetic testing is crucial because phenotypic overlap exists among neuromuscular diseases, and precise diagnosis determines cardiovascular monitoring protocols 1

Cardiac Involvement (Most High-Yield for Morbidity/Mortality)

Approximately 70% of BMD patients develop dilated cardiomyopathy, predominantly in the third decade or later, and cardiac death is MORE common in BMD than DMD. 1

Cardiac Screening Protocol

• Cardiac evaluation should begin at diagnosis regardless of age 1
• Only a small percentage (<16 years) have symptoms before age 16, but ≈70% develop symptomatic heart failure by age 40 1
• Echocardiography is the primary screening modality—electrocardiography alone should NOT replace echo for detecting preclinical LV dysfunction 1
• Ongoing cardiac surveillance is mandatory because therapeutic intervention before symptom onset has greater impact 1

Critical Cardiac Pearls

• Female carriers should undergo cardiac evaluation with ANY symptoms 1
• At mean age 44 years, carriers show decreased LVEF and myocardial fibrosis 1
• Cardiac evaluation must occur within 3-6 months before any anesthesia/sedation in patients with suspected cardiac involvement 1
• Anesthesia should be performed by experienced anesthesiologist in center with appropriate ICU facilities 1

Management Differences from DMD

BMD patients are NOT typically treated with glucocorticoids, unlike DMD patients. 1

Key Management Points

• No routine glucocorticoid therapy for BMD (this distinguishes it from DMD management) 1
• Multidisciplinary team approach involving neurology and cardiology with NMD expertise 1
• Referral to cardiologist with NMD expertise or at minimum a collaborative HF specialist 1

Common Step 2 Pitfalls to Avoid

• Do NOT assume cardiac severity correlates with skeletal muscle involvement—they are dissociated in BMD 1
• Do NOT rely on ECG alone for cardiac screening—echocardiography is mandatory 1
• Do NOT forget preoperative cardiac evaluation—this is a Class I recommendation 1
• Do NOT overlook female carriers—they require cardiac evaluation with symptoms 1
• Do NOT prescribe glucocorticoids for BMD—this is a DMD-specific therapy 1

Prognosis and Natural History

• BMD has milder, more variable phenotype than DMD with later onset 1
• Cardiac death is more common in BMD than DMD (DMD patients often succumb to respiratory failure first) 1
• When cardiomyopathy presents in childhood, it tends to be more severe and progress more rapidly than typical adult-onset BMD cardiomyopathy 1