This document provides information on various types of muscular dystrophies. It focuses on Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). DMD is caused by the absence of the dystrophin protein due to mutations in the dystrophin gene, leading to muscle degeneration. It presents in childhood with weakness and pseudohypertrophy. BMD is less severe and variable as it produces an altered dystrophin protein. The document also briefly discusses polymyositis.

1. Muscular
Dystrophies
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2. MUSCULAR DYSTROPHY
Heterogeneous group
 Inherited disorders
Often presenting in childhood
Progressive degeneration of muscle fibers
Muscle weakness and wasting
2

3. Muscular dystrophy (Types)
1. X-linked muscular dystrophy : a) Duchenne
muscular dystrophy b) Becker muscular
dystrophy
2. Autosomal muscular dystrophies a) Limb girdle
muscular dystrophies b) Facioscapular humeral
muscular dystrophy c) Oculopharyngeal muscular
dystrophy
3. Myotonic dystrophy

4. MUSCULAR DYSTROPHY
Two most common ones are:
X-linked muscular dystrophy:
Duchenne muscular dystrophy (DMD)
Becker muscular dystrophy (BMD)
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5. Duchenne muscular dystrophy
DMD
5

6. French neurologist Guillaume Benjamin Amand Duchenne
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7. Duchenne muscular dystrophy
X-linked recessive
Absence of a structural protein termed
DYSTROPHIN
Most common and severe form of muscular
dystrophy
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8. Pathogenesis
• Absence of dystrophin
due to frameshift
mutation of the
dystrophin gene on the
X chromosome.
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9. Pathogenesis
 Dystrophin protein is found in skeletal and cardiac muscle
 Dystrophin is a part of dystrophin-glycoprotein complex
 Dystrophin-glycoprotein complex damage results in influx of
ca++ ions
 Increased cytosolic ca++ ions stimulates calpains
 Results in muscle proteolysis (Necrosis)
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10. Pathogenesis
Results in :
 Degeneration and Regeneration of muscle fibres.
Finally,
Muscles fibres are replaced by connective fibrous
tissue and adipose tissue
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11. Clinical features
 Normal at birth, Onset of symptoms by age 5
 Waddling gait (Duck like)
 Wheelchair-bound by age 10
 Proximal weakness of shoulder and pelvic girdles
 Calf pseudo-hypertrophy (muscles replaced by fat and
connective tissue )
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12. Calf pseudo-hypertrophy

13. 13

15. Waddling gait

16. Clinical features
Heart failure and arrhythmias may occur
Respiratory insufficiency and pulmonary
infections
Death due to respiratory failure by the second or third
decade
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17. Diagnosis
Initially Elevated serum Creatine kinase
Later, Decreased when the disease progresses.
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18. Diagnosis
Morphology
o Muscle fibers of various sizes
o Necrosis, degeneration and regeneration of fibers
o Fibrosis
o Fatty infiltration
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19. Normal Muscle DMD
Hypertrophy
Degeneration of muscle fibres
Fibrosis
Chronic inflammatory cells
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20. Diagnosis
Immunostain: Decreased dystrophin protein
 PCR : DNA analysis
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21. Immunoperoxidase stain revealing
dystrophin in normal muscle
Immunoperoxidase stain – absence of
dystrophin
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22. 22

23. 23

24. 24Reetu Baral MD

25. Gower maneuver

26. Becker’s muscular dystrophy
BMD
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27. Less common and not as severe as Duchenne’s.
Mutation produces an altered dystrophin protein.
Later onset with variable progression.
Cardiac involvement is rare
May have a relatively normal life span.
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28. Immunoperoxidasestain revealing dystrophin in normal muscle
BMD : Dystrophin, present in small amounts
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29. Polymyositis (PM)
Epidemiology
Female dominant
Age: 40 to 60 years
Race: Black>White
Increased risk of malignant neoplasms (Particularly
lung and bladder cancer and Non-Hodgkin’s
lymphoma)

30. Polymyositis (PM)
Etiology and Pathogenesis
(A)
 Triggers e.g. viruses (HIV, HTLV-1&Coxsackie virus B)
 The viruses damage skeletal muscle, leading to altered class I
& class II MHC antigens.
 Cytotoxic CD8 T cells (predominant cell) and CD4TH1 subset
cells activate macrophages
 Destruction of myocyte fibres in skeletal muscle.

31. Polymyositis (PM)
Etiology and Pathogenesis
(B)
 Autoantibodies are directed against transfer RNA synthetases
and other nuclear and cytoplasmic antigens in skeletal muscle.

32. Polymyositis (PM)
Clinical findings :
1. Constitutional signs: Fever, morning stiffness, fatigue and
weight loss
2. Symmetrical, proximal muscle weakness (with or without
pain) in both the upper and lower extremities, trunk,
shoulders and hips
3. Dysphagia: For solids and liquids
4. Respiratory symptoms: Related to interstitial lung disease

33. Polymyositis (PM)
Laboratory findings :
1. Serum creatine kinase and aldolase: Markedly increased.
2. Antibody findings – Serum ANA
- Anti transfer RNA synthetase (J0-1)
antibodies
3. Electromyography: Myopathic dysfunction
4. Muscle biopsies:
Microscopic
 Necrotic and regenerating muscles and lymphocytic and
macrophage infiltrate.