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