Becker Muscular dystrophy
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
