Motor

Myopathy

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Myopathy, Myositis

  • Definitions
  1. Myopathy
    1. Non-cancer disorder affecting skeletal or smooth muscle
  2. Myositis
    1. Inflammation of skeletal muscles
  • Findings
  1. Suggestive of Myopathy
    1. Gradual onset of symmetric weakness
    2. Proximal weakness
      1. Difficulty combing hair
      2. Difficulty walking up stairs
    3. Neck Flexion weaker than neck extension
    4. Deep Tendon Reflexes preserved
  2. Suggestive of alternative diagnosis (i.e. Neuropathy)
    1. Sudden onset of asymmetric weakness
    2. Paresthesias in extremities
    3. Bowel dysfunction (e.g. Stool Incontinence)
    4. Bladder dysfunction (e.g. Urinary Incontinence)
    5. Distal weakness suggests Neuropathy
      1. Except in Guillain-Barre, Myotonic Dystrophy
    6. Deep Tendon Reflexes lost
  • History
  • Direct to specific Myopathy
  1. Family History of Myopathy: Muscular Dystrophy
  2. Difficult swallowing: Polymyositis
  3. Weakness varies and includes eyes: Myasthenia Gravis
  4. Age of onset
    1. Age <30: Muscular Dystrophy
  • Labs
  1. Creatine Phosphokinase (CPK) increased
  2. Aspartate Aminotransferase (AST) may be increased
  3. Aldolase may be increased
  4. Lactate Dehydrogenase (LDH) may be increased
  • Diagnostics
  1. Electromyogram (EMG)
  2. Nerve Conduction Studies (NCS)
  3. Muscle biopsy
  • Causes
  1. See Myopathy Causes
  2. See Polymyositis Differential Diagnosis
  3. See Medication Causes of Myositis
  4. See Muscular Dystrophy
  5. See Muscle Weakness in Children (Pediatric Neuromuscular Disorders)
  6. See Acute Motor Weakness Causes
    1. Critical to rule-out emergent causes
  7. Infectious Myositis
    1. Viral Myositis
      1. Influenza (esp. affecting calf muscles, with "Charlie-Chaplain shuffle" with Out-toeing)
    2. Bacterial Myositis (pyomyositis)
      1. Focal infection (esp. upper thigh or deep Pelvis)
      2. Gram Positive infection (esp. Staphylococcus) in most cases
      3. May be associated with underlying Osteomyelitis
  8. Treatable myopathies
    1. Thyroid Myopathy (Hypothyroidism, Hyperthyroidism)
    2. Polymyositis
    3. Critical Illness Myopathy
    4. Drug Induced Myositis
      1. Alcoholic Myopathy
      2. Statin-Induced Myopathy
      3. Steroid Myopathy
    5. Hypokalemic Periodic Paralysis
    6. Polymyalgia Rheumatica
    7. Myasthenia Gravis
    8. Eaton-Lambert Syndrome