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Muscular Dystrophies (Dystrophy means – abnormal growth Q)

A muscular dystrophy is distinguished from all other neuromuscular disease by four obligatory criteria

  1. It is a primary myopathy
  2. It has a genetic basis
  3. Course is progressive
  4. Degeneration and death of muscle fibers occur at some stage in the disease

Characteristic features of muscular dystrophies


Genetics; characteristic features

Age at onset




Xp-linked recessive;

Pseudohypertrophy of calf muscles, subnormal intelligence

2-5 year

Pelvic girdle; shoulder girdle and heart



Xp-linked recessive;

Pseudohypertrophy; pes cavus

8-10 years

Pelvic girdle


Emery Dreifuss

Xq 28 linked recessive autosomal dominant; cardiac arrhythmias

5-15 years

Biceps, triceps and peroneal muscle


Limb girdle

Autosomal recessive / sominant

10-30 years

Pelvic and shoulder girdles



Autosomal recessive / dominant

12-30 years

Gastrocnemius; mainly distal muscles


Myotonic dystrophy

Autosomal dominant (19q13.3)

Newborn to adult

Face, girdles, sternocleidomastoid

Slow, multisystem involvement


1. Duchhene Muscular Dystrophy

  1. X-linked recessive trait.
  2. It is caused by a mutation of the gene that cause dystrophin protein localized to the inner surface sarcolema of the muscle. Q
  3. Dystrophin – glycoprotein complex (sacroglycan and dystroglycan) appears to confer stability to the sarcolemma, disruption of the dystrophin – glycoprotein complex weakens the sarcolemma, causing membrane tears and a cascade of events leading to muscle fiber necrosis. This sequence of event occurs repeatedly during the life of a patient with muscular dystrophy.
  4. The abnormal gene is on the X chromosome at the Xp21 locus and is one of the largest gene identifiedQ
  5. Rarely symptomatic at birthQ or early infancy early gross motor skills such as rolling over, sitting and standing are usually achieved at appropriate time or may be mildly delayed.
  6. Poor head control in infancy may be the first sign of weakness
  7. Gowers sign is often evident by the age 3 year and is fully expressed by age 5 or 6 year. Q
  8. Enlargement of the calves (pseudohypertrophy) and wasting of thigh muscles is a classic feature. After calves, the next most common site of muscular hypertrophy is the tongue followed by muscle of forearm
  9. Unless ankle contractures are severe, ankle jerks remain well preserved until terminal stages. In upper extremities, the brachioradialis reflex is usually stronger than the biceps or triceps.
  10. Cardiomyopathy is a constant feature of this disease. The severity of cardiac involvement does not necessarily correlate with the degree of skeletal muscle weakness.
  11. Some intellectual impairment occurs in all patientsQ
  12. Death occurs usually at about 18 year of age. The causes of death are respiratory failure in sleep intractable heart failure, pneumonia or occasionally aspiration. 

Lab Finding

  1. CPK levels elevated – 15,000 – 35,000 IU/L (N<160)
  2. Aldolase and AST also elevated.
  3. NCV – Normal
  4. Biopsy is needed for definite diagnosis.

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