- Differentials
- Neurological
- Inflammatory
- Polymyositis
- Dermatomyositis
- Inclusion body myositis
- Juvenile dermatomyositis
- Vasculitis
- Overlap syndromes- lupus, scleroderma, rheumatoid arthritis, Sjögren’s syndrome
- Rheumatoid arthritis, Sjögren’s syndrome
- Endocrine disorders
- Hypothyroidism
- Cushing’s syndrome (or exogenous steroid administration)
- Electrolyte disorders
- Hypokalemia
- Hypophosphatemia
- Hypocalcemia
- Hypernatremia or hyponatremia
- B12 deficinecy
- Metabolic myopathies
- Disorders of carbohydrate, lipid, and purine metabolism
- Drugs and toxins
- Illicit drugs- cocaine, heroin
- Alcohol
- Corticosteroids
- Other- colchicine, antimalarial drugs, HMG-CoA reductase inhibitors, penicillamine, zidovudine
- Infections
- Viral- influenza, parainfluenza, Coxsackie, HIV, cytomegalovirus, echovirus, adenovirus, Epstein Barr virus
- Bacterial- pyomyositis, lyme myositis
- Fungal
- Parasitic- trichinosis, toxoplasmosis
- Rhabdomyolysis
- Crush trauma
- Seizures
- Alcohol abuse, including hyperkinetic state with delirium tremens
- Exertion, especially with environmental heat illness
- Vascular surgery
- Malignant hyperthermia
- History to consider
- Pattern of onset – timing, areas, symmetry, proximal or distal
- Variations or fluctuations – fatiguability, diurnal changes
- Temporal spread
- Associated symptoms – pain/sensory, muscle wasting, cramps
- Medical history
- Family history
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