Learning objectives
Different types and classifications of Muscle disorders
Mechanisms associated with different myopathies
Electromyographic presentation of myopathies
Duchene Muscular dystrophy
Polymyositis – Classification
Drugs causing the myopathy
Lecture outline
Muscle Disorders
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Myopathy
Muscular dystrophy
Myositis
Myotonia
Classification of Myopathies
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Hereditary
Congenital
Muscle Energy Metabolism Disorders
Mitochondrial
Muscle Membrane Excitability Disorders (Channelopathies)
Inflammatory
Endocrine & Metabolic
Drug Induced
Mechanisms of Muscle Disease
• Metabolic or contractile elements of muscles do not react
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• Congenital abnormalities of muscle membrane proteins
• Interference with energy provision
• Contracted muscle may fail to relax
• Increased threshold of mechanical activation
• Defects of Cl-, Na+ Ca++ channels
Effects of Muscle Disease
CLINICAL:
• Proximal weakness & wasting
• Pain, stiffness, & tenderness
• Waddling gait.
• Normal reflexes & sensations.
Laboratory:
• Elevated muscle enzymes: CPK & aldolase.
• Circulating antibodies
ELCTROPHYSIOLOGICAL
• Increased or decreased insertional activity.
• Abnormal spontaneous activity during relaxation.
• Abnormalities in amplitude, duration & shape of single MUPs.
• Decrease in no of MUPs & change in firing pattern.
• Variation in MUPs during voluntary activity.
• Special phenomena, e.g. electrical silence during contracture.
Investigations
• Serum CK
• Electrodiagnosis
– EMG
– NCS
• Muscle biopsy
•DNA-based testing
DUCHENNE MUSCULAR DYSTROPHY
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X-linked recessive disorder.
Commonest dystrophy: 1 in every 3000 male infants.
Absence of dystrophin, a structural sarcolemmal protein.
Female carries may be mildly affected.
Enlargement of muscles in early disease is followed by eventual
wasting.
• Loss of ambulation between 8 and 12 years
• Death in late teens from respiratory insufficiency or pneumonia
Clinical Features
• Healthy males at birth, apparent around 4-5y
• Delayed milestones.
• Myopathic features.
• Hypertrophied calves.
• Toe walking
• Exaggerated lumbar lordosis.
• Usual sparing of bulbar muscles.
Congenital Myopathies
• Hypotonic (floppy) or weak infant
• Usually non-progressive or slowly progressive
• Unusual morphological changes in muscle fibers
POLYMYOSITIS
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Inflammatory myopathy
Symmetric
Progressive over weeks to months.
Females predominantly affected. 2:1.
Painless (>50%) weakness of proximal limb muscles.
Mostly a disease of adults
Rare before 20 years.
Polymyositis
Classification:
• Polymyositis (PM)
• Dermatomyositis (DM)
• PM or DM associated with malignancy.
• Childhood PM or DM associated with vasculitis
• PM or DM associated with CT disorder.
Drugs that may cause myopathy
Lipid lowering agents
• Statins
• Fibrates
• Nicotinic acid
• Ezetimibe
Glucocorticoids
• Prednisone and prednisolone
• Methylprednisolone
• Dexamethasone
• Inhaled steroids
Anti-rheumatic drugs
• Colchicine
• Chloroquine
• Hydroxychloroquine
Cardiovascular drugs
• Amiodarone
• Perhexiline
Other drugs
• Emetine
• ∑-aminocaproic acid
• Etretinate
• Zidovudine
• Interferon-α
• D-penicillamine
• Streptokinase