Makindo Medical Notes

Becker Muscular Dystrophy (BMD) is a neuromuscular disorder and a milder allelic variant of Duchenne Muscular Dystrophy (DMD). It is caused by mutations at Xp21 on the X chromosome → producing reduced, partially functional dystrophin. 👉 This leads to slower progression and later onset compared to DMD.

• X-linked recessive inheritance (affects males, females are carriers). 👨‍🦱
• Dystrophin deficiency → fragile muscle fibres, repeated injury and degeneration.
• BMD patients often survive into adulthood, unlike DMD. ⏳

🧑‍⚕️ Clinical Presentation

• Progression: Similar to DMD but slower; ambulation often preserved into teens or 20s.
• Weakness: Proximal muscle weakness (hips, shoulders) → difficulty climbing stairs, running, or rising from the floor (Gower’s sign). 🪜
• Pain & Cramps: Exercise-related myalgia and cramps are common.
• Physical Findings: Calf enlargement (pseudo-hypertrophy) and progressive proximal wasting.
• Cardiac Involvement: Dilated cardiomyopathy and arrhythmias may precede severe skeletal weakness. ❤️

🔎 Investigations

• Creatine Kinase (CK): Elevated 10–100× above normal (marker of muscle breakdown). 🧪
• ECG & Echocardiogram: Early screening for cardiomyopathy and conduction defects.
• Electromyography (EMG): Myopathic pattern (small, polyphasic motor units) → distinguishes from neuropathic causes.
• Muscle Biopsy: Shows dystrophic changes with reduced (but not absent) dystrophin on immunohistochemistry. 🧫
• Genetic Testing: Confirms dystrophin gene mutation; distinguishes from DMD (frame rule: out-of-frame = DMD, in-frame = BMD).

💊 Management

• Multidisciplinary care is essential (neurology, cardiology, physiotherapy, respiratory). 🏥
• Physiotherapy & Exercise: Stretching & orthoses to reduce contractures and maintain mobility.
• Cardiac Monitoring: ACE inhibitors, β-blockers if cardiomyopathy develops.
• Respiratory Care: Non-invasive ventilation for advanced respiratory weakness.
• Orthopaedic Support: Correct scoliosis or postural deformities if present.
• Genetic Counselling: X-linked inheritance → carrier testing & family planning advice.

📉 Prognosis

• Slower progression than DMD, but eventual loss of ambulation common by mid-20s to 40s.
• Cardiac disease is the major cause of morbidity and mortality. ⚠️
• Many patients live into middle age with good supportive care.

💡 Exam Pearls

• BMD vs DMD: DMD = absent dystrophin, early severe disease. BMD = reduced dystrophin, slower course. • Key clue: Male adolescent with calf pseudo-hypertrophy + high CK. • Cause of death: Cardiomyopathy > respiratory failure.

📚 References

• GeneReviews – Becker Muscular Dystrophy
• Muscular Dystrophy Association – BMD Overview