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Muscle Weakness

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Muscle Weakness

  • Evaluation
  1. Distinguish weakness from Fatigue and Asthenia
    1. Asthenia is exhaustion without weakness
    2. Fatigue is inability to perform task repeatedly
    3. Weakness is inability to perform task initially
  2. Determine distribution
    1. Unilateral, focal weakness
      1. Mononeuropathy (focal Peripheral Neuropathy)
      2. Multiple Sclerosis
      3. Cerebrovascular Accident (CVA)
    2. Symmetric proximal weakness
      1. Myopathy
    3. Symmetric distal weakness
      1. Polyneuropathy
      2. Amyotrophic Lateral Sclerosis
      3. Guillain-Barre Syndrome
      4. Myopathy less commonly effects distal muscles
        1. Statins, Alcohol may effect distal and proximal
        2. Inclusion body Myositis
        3. Myotonic dystrophy
  3. Consider specific causes
    1. See Muscle Weakness Causes
    2. See Neuropathy
    3. See Toxic Myopathy
  • Diagnostic evaluation based on category
  1. See Neuropathy
  2. Myopathy (see also Polymyositis)
    1. Creatine Kinase (CPK)
    2. Erythrocyte Sedimentation Rate
    3. Serum chemistry (e.g. Chem 8)
      1. Electrolytes Glucose, calcium, Magnesium, phosphate
    4. Thyroid Stimulating Hormone (TSH)
    5. Other tests as indicated
      1. 24-hour urine cortisol
      2. Growth Hormone
      3. Antinuclear Antibody
    6. Definitive testing
      1. Electromyogram
      2. Muscle Biopsy