Polymyositis and dermatomyositis laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sadaf Sharfaei M.D.[2]


Elevated sarcoplasmic enzymes are consistent with the diagnosis of polymyositis and dermatomyositis which include creatine phosphokinase, aldolase, transaminases, lactic dehydrogenase, and myoglobin. High white blood cell counts, low lymphocytes, and low hematocrit levels might be detected on CBC. Low albumin levels, high ESR and high IgM and IgG levels could be seen in patients with polymyositis and dermatomyositis. 20 myositis-specific autoantibodies are identified in patients with polymyositis and dermatomyositis. Anti-Jo-1 antibody is the most frequent myositis-specific autoantibodies which causes antisynthetase syndrome. Anti Mi-2 might be seen frequently in patients with dermatomyositis. Anti-SRP antibody is associated with very poor prognosis. Some of these myositis-specific autoantibodies are associated with malignancy. Anti-HMGCR antibody might be elevated in patients with statin-associated necrotizing autoimmune myopathy (SANAM).

Laboratory Findings

Routine test

Sarcoplasmic enzymes

Myositis-specific autoantibodies

Autoantibody Antigen Features Frequency
Antisynthetase Anti-Jo-1 Histidyl-tRNA synthetase
  • Antisynthetase syndrome
    • Arthritis
    • Interstitial lung disease
    • Fever
    • Mechanic's hands
    • Raynaud's phenomenon
  • Flare up in spring
  • Moderate response to treatment
  • Poor prognosis
  • Associated with epstein-Barr virus (EBV), adenovirus, and influenza infection
Anti-PL-7 Threonyl-tRNA synthetase
  • Myositis, mechanic's hands, Gottron's papules, arthritis
Anti PL-12 Alanyl-tRNA synthetase
  • Fever, Raynaud's phenomenon, high frequency of ILD
  • Epstein-Barr virus (EBV), adenovirus, and influenza infection
Anti-EJ Glycyl-tRNA synthetase  5-10%
Anti-OJ Isoleucyl-tRNA synthetase <5%
Anti-KS Asparaginyl-tRNA synthetase <5%
Anti-Ha Tyrosyl-tRNA synthetase <1%
Anti-Zo Phenylalanyl-tRNA synthetase <1%
Others Anti Mi-2 Chromodomain helicase DNA binding protein 4
  • Dermatomyositis rash without significant lung involvement
  • Acute but mild onset
  • Good prognosis
Anti-SRP Signal recognition particle
  • Cardiac involvement
  • Necrotizing myopathy
  • Flare up in fall
  • Very acute and severe onset
  • Poor response to treatment
  • Very poor prognosis
Anti-p155/140 Transcriptional intermediary factor 1-gamma
  • Cancer-associated myositis
  • Juvenile dermatomyositis
  • Severe cutaneous disease
13-21% in IIM

23-29% in JDM

Anti-MJ Nuclear matrix protein (NXP-2)
  • Cancer-associated myositis
  • Juvenile dermatomyositis
23% in JDM
Anti-SAE Small ubiquitin-like modifier activating enzyme
  • Cancer-associated myositis
Anti-caDM-140 Intracytoplasmic MDA5
  • Dermatomyositis and rapidly progressive ILD
50% (C-ADM)
Anti-PMS1 DNA mismatch repair enzyme 7.5%
Anti-HMGCR 3-hydroxy-3-methylglutaryl-coenzyme A reductase
  • Statin-associated necrotizing autoimmune myopathy (SANAM)
Anti-FER Elongation factor 1 alpha
Anti-KJ Unidentified cytoplasmic protein 
Anti-MAS Unidentified cytoplasmic RNA
  • Overlap of polymyositis and Scleroderma


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