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Duchenne's Muscular Dystrophy Clinical Features
- X-linked recessive so boys only
- normal at birth but symptoms at onset of walking, wheelchair by 12 years on average
- calf pseudohypertrophy (firm, rubbery)
- cardiac abnormalities
- respiratory deterioration due to scoliosis
- mild cognitive impairment
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Becker's Muscular Dystrophy Clinical Features
- similar to Duchenne's but milder
- symptom onset-- about 12 years old complain of muscle cramps, some not until 4th decade or later
- cardiomyopathy common, cognition usually normal
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Dystrophin Deficiency Pathology/Pathophysiology
degeneration and phagocytosis of single muscle fibers or groups of fibers
dystrophin thought to stabilize the muscle membrane during contraction/relaxation
- Duchenne's-- deletion in dystrophin gene
- Becker's-- dystrophin present but structurally abnormal
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Dystrophin Deficiency Dx
- increased creatine kinase
- EMG
- genetic testing
- if dystrophin deletion not detected-- muscle biopsy
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Dystrophin Deficiency Tx
- prednisone for Duchenne's, not used for Becker's
- supportive care
- gene therapy
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Limb girdle muscular dystrophies
- various mutations in dystrophin associated proteins and other muscle proteins
- specific mutation influences age of onset and pattern of muscle involvement
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Myotonic Dystrophy Clinical Features
- autosomal dominant
- weakness and atrophy (especially across face)
- myotonia
- multisystem abnormalities
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Myotonic Dystrophy Pathogenesis
- elongated trinucleotide repeat (CUG)
- abnormal RNA transcript binds to proteins involved in RNA-splicing (interferes with other genes)
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Myotonic Dystrophy Dx and Rx
Dx- EMG, genetic testing
Rx- primarily supportive, ion channel blocker if myotonia substantial enough
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Non-dystrophic hereditary myopathies
- abnormal glycogen metabolism
- phosphofructokinase deficiency
- mitochondrial myopathies
- channelopathies
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Dermatomyositis and Polymyositis Clinical Features
- symmetric proximal muscle wasting and weakness
- progresses gradually (weeks) for DM and (months) PM
- DM-- characteristic rash on face and hands, children and young adults, malignancy in 10-20%
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Inclusion Body Myositis Clinical Features
- prominent involvement forearm flexors and knee extensors
- asymmetric issues, asymmetric dysphagia common
- after age 50
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Inflammatory Myopathies Pathology
- segmental muscle fiber necrosis
- muscle fiber regeneration
- mononuclear cell inflammation
- IBM-- vacuolar inclusion containing beta amyloid, tau, and TDP-43 in muscle fibers
- DM- perivascular inflammation, microinfart
- PM- inflammatory cells among muscle fibers
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Inflammatory Myopathies Dx
- increase CK
- EMG
- muscle bx for definitive Dx
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Inflammatory Myopathies Management
- DM/PM prednisone
- IBM none known
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