Muscular dystrophy
Definition: Muscular dystrophies are a group of inherited progressive muscle disorders characterized by muscle fiber degeneration and weakness, with replacement of muscle by fat and connective tissue.
They are primary myopathies (muscle diseases), not disorders of nerves or motor neurons.
Classification
1. Duchenne Muscular Dystrophy (DMD): Most common muscular dystrophy. X-linked recessive. Complete absence of dystrophin
2. Becker Muscular Dystrophy (BMD): X-linked recessive. Reduced/abnormal dystrophin. Milder and later onset than DMD
3. Limb-Girdle Muscular Dystrophy: Shoulder and pelvic girdle weakness
4. Facioscapulohumeral Muscular Dystrophy (FSHD): Face + shoulder girdle involvement
5. Myotonic Dystrophy: Weakness + myotonia (delayed muscle relaxation)
Pathogenesis
Dystrophin Deficiency
- Dystrophin stabilizes muscle cell membranes.
- Absence/defect of dystrophin →
- Muscle fiber necrosis
- Progressive muscle degeneration
- Fatty replacement
- Loss of muscle function
1.Duchenne Muscular Dystrophy (Most Important)
Clinical Features
- Onset: Early childhood (2–5 years)
- Muscle Weakness: Progressive. Proximal muscles affected first. Pelvic girdle > shoulder girdle
Typical Findings: Delayed walking. Frequent falls. Difficulty climbing stairs. Waddling gait
Gowers Sign: Child uses hands to "climb up" the thighs when rising from the floor due to proximal weakness.
Pseudohypertrophy: Enlarged calves.Due to fat and connective tissue replacement
Late Manifestations: Contractures. Scoliosis.Cardiomyopathy. Respiratory failure
2.Becker Muscular Dystrophy
Features: Similar to DMD but milder. Later onset (adolescence/adulthood). Slower progression. Longer survival
Examination Findings
- Motor System: Symmetrical proximal weakness. Muscle wasting. Reduced muscle strength
- Reflexes: Decreased late in disease. No Babinski sign
- Sensation: Normal (important distinction from neuropathies)
Diagnosis
- Serum Creatine Kinase (CK): Markedly elevated. Especially in DMD
- Genetic Testing: Confirms dystrophin gene mutation
- Electromyography (EMG)
- Myopathic pattern: Small, short-duration motor unit potentials
- Muscle Biopsy: Muscle fiber degeneration. Reduced/absent dystrophin staining
Differential Diagnosis
1. Spinal Muscular Atrophy: LMN signs. Fasciculations. Neurogenic EMG
2. Myasthenia Gravis: Fluctuating weakness. No muscle wasting early
3. Inflammatory Myopathies: Muscle pain. Elevated inflammatory markers
Treatment
- No Cure
- Supportive Management: Physiotherapy. Orthopedic management. Respiratory support
- Medications: Corticosteroids (DMD). Prednisone. Deflazacort
- Cardiac Care: Regular cardiac monitoring
Prognosis
1.DMD: Progressive disability. Wheelchair dependence in adolescence. Death usually from respiratory or cardiac failure
2.BMD: Slower progression. Longer life expectancy