Myopathies Workup

Updated: Jul 08, 2022
  • Author: Courtney A Bethel, MD, MPH; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Laboratory Studies

The following laboratory tests may be used to evaluate patients with myopathies:

  • Creatine kinase (CK) with isoenzymes
  • Electrolytes (calcium, magnesium)
  • Serum myoglobin
  • Serum creatinine and blood urea nitrogen (BUN)
  • Urinalysis - Myoglobinuria is indicated by positive urinalysis with few red blood cells (RBCs) on microscopic evaluation.
  • Complete blood count (CBC)
  • Erythrocyte sedimentation rate (ESR)/C-reactive protein (CRP)
  • Thyroid function tests
  • Aspartate aminotransferase (AST)

Testing for myositis-specific autoantibodies along with use of the European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria for idiopathic inflammatory myopathies (IIM) appears to improve the accuracy of identifying affected patients and IIM subtypes. [14]


Other Tests


Electrocardiographic (ECG) findings suggestive of hypokalemia include the following:

  • Diffuse nonspecific ST-T wave changes
  • Increased PR interval
  • U waves
  • Wide QRS

Other studies

Steroid therapy should be withheld until a definitive diagnosis is made, but many tests that are essential for distinguishing among the varied causes of myopathy are out of the scope of the emergency physician. These tests include the following:

  • Genetic testing
  • Antinuclear antibody (ANA) [15, 16]
  • Magnetic resonance imaging (MRI) [15]
  • Electromyography (EMG)
  • Muscle biopsy [15, 17]

Electrodiagnostic studies effectively diagnose critical illness myopathy (CIM) and critical illness polyneuropathy (CIP) as well as identify conditions that mimick them, but intensive care units do not appear to have a standard approach for evaluation of CIM/CIP, and electrodiagnostic studies are not often ordered. [18]