Affecting Muscle Tissue

Inheritance

Gene defect

Duchenne’s

X-linked recessive

Xp21 dystrophin, point deletion, nonsense mutation, no dystrophin protein produced

Becker’s

X-linked recessive

Xp21 dystrophin in noncoding region with normal reading frame, lesser amounts of truncated dystrophin produced

Facioscapulohumeral (FSH), adult

4q35

Infantile FSH

Unknown

The muscles get degenerated with subsequent loss of fiber, proliferation of connective tissue, and subsequently of adipose tissue.

Classification

Sex-linked muscular dystrophy
- Duchenne
- Becker
- Emery-Dreifuss
Autosomal recessive muscular dystrophy
- Limb-girdle
- Infantile facioscapulohumeral
Autosomal dominant muscular dystrophy
- Facioscapulohumeral
- Distal
- Ocular
- Oculopharyngeal

Evaluation

Hematologic studies – The serum CPK is markedly elevated in the early stages of Duchenne muscular dystrophy. This may be 200–300 times the normal value but decreases as the disease progresses and muscle mass is reduced.
Electromyography shows characteristic myopathic changes with reduced amplitude, short duration, and polyphasic motor action potentials.
Muscle biopsy material is usually examined by routine histology, special histochemical stains, and electron microscopy. Muscles that are involved but functioning are selected.
More recently, molecular genetic testing has become equally, if not more, important.

1.1 Duchenne Muscular Dystrophy

Overview

The most common form of muscular dystrophy. The disease is characterized by its occurrence in males.
Occurs in approximately 1/3,500 live male births.

Evaluation

Becomes clinically evident when the child is between 3 and 6 years of age. They may demonstrate frequent episodes of falling, with inability to hop and jump normally.
Progressive weakness in proximal muscle groups which descends symmetrically in both lower extremities, particularly the gluteus maximus, gluteus medius, quadriceps, and tibialis anterior muscles.
Pseudohypertrophy of calf is common.
Cardiac involvement is common.
Patients develop a waddling, wide-based gait with shoulder sway.
Weakness in the shoulder girdle occurs around 3–5 years later. Tendency for child to slip a truncal grasp has been termed “Meyerson sign.”
Absence of sensory deficits.
Gower sign: valuable clinical sign – Patient is asked to rise from sitting position on the floor. The patient walks his or her hands up their extremities to compensate for the quadriceps or gluteus weakness.
Contracture of tendoachilles and IT band are the most consistent deformities.

Management

Efforts should be made to maintain a daily ambulation program. They progress slowly but continuously. They are usually unable to ambulate effectively by 10 years of age in absence of treatment.
Orthopedic problems in DMD include decreasing ambulatory ability, soft tissue contractures, and spinal deformity.
Corticosteroid therapy – Prolongs ambulation and slows the deterioration of forced vital capacity (FVC). Treatment carries a high risk of complications.
Nighttime ventilation significantly prolongs survival.
Physical therapy and orthosis – Maximum resistance exercises performed several times a day.
Serial casting may be useful to correct existing deformities; knee flexion contractures of less than 30° may benefit by serial or wedge casting. Orthoses need to be used after casting to maintain correction.
Surgical Intervention
- Surgery is controversial in DMD. It can be done when contractures are painful or interfere with essential daily activities.
- If surgery is performed, the focus should be on early postoperative mobilization and ambulation to prevent deconditioning and deterioration.
- Major contractures include equinus and equinovarus contractures of ankle and foot, knee flexion contractures, and hip flexion and abduction contractures. Contracture releases should be performed when child is still ambulatory.
- Scoliosis develops in 95 % of patients after they transition to a wheelchair (usually around age 12 years). Early posterior instrumented fusion (at 20°) is recommended before loss of FVC occurs due to respiratory muscle weakness and progressively decreasing cardiac output. Stiff curves may require anterior and posterior fusion.

Complications

Malignant hyperthermia is common intraoperatively and is pretreated with dantrolene at surgery.

1.2 Becker’s Muscular Dystrophy

Overview

Less common that DMD. Occurs in 1 in 30,000 live male births.
It is similar to Duchenne muscular dystrophy in clinical appearance and distribution of weakness but is less severe.

Evaluation

Onset is generally after 7 years of age; rate of progression is slower. Patients usually remain ambulatory till adolescence or early adult years.
Pseudohypertrophy of calf is common. Cardiac involvement is frequent.
Life expectancy is longer.

Treatment

Treatment is essentially the same as DMD. Incidence of scoliosis is high. Patients require periodic spinal radiographs.

1.3 Facioscapulohumeral Muscular Dystrophy

Overview

Autosomal dominant disorder manifested by muscular weakness of face, shoulder girdle, and upper arm.
Onset can occur at any age but is most common in late childhood or early adulthood.
Can occur in both genders but is more common in females.
Life expectancy is relatively good.

Evaluation

Face has a “popeye” appearance. Lack of mobility, incomplete eye closure, pouting lips with a transverse smile, and absence of eye and forehead wrinkles.
Shoulder and girdle weakness leads to scapular winging.
Forward-sloping appearance of the shoulders, clavicles assume a horizontal position.
Decreased scapulothoracic motion, glenohumeral motion is usual preserved.