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]

Overview

An elevated/reduced concentration of serum/blood/urinary/CSF/other [lab test] is diagnostic of [disease name].

OR

Laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].

OR

[Test] is usually normal for patients with [disease name].

OR

Some patients with [disease name] may have elevated/reduced concentration of [test], which is usually suggestive of [progression/complication].

OR

There are no diagnostic laboratory findings associated with [disease name].

Laboratory Findings

• Different laboratory tests may be used to diagnose polymyositis and dermatomyositis and exclude other myopathies which include:
  • Sarcoplasmic enzymes
  • Myositis-specific autoantibodies

Sarcoplasmic enzymes

• Sarcoplasmic enzymes consistent with the diagnosis of polymyositis and dermatomyositis include:

• • Creatine phosphokinase
  • Aldolase
  • Transaminases
  • Lactic dehydrogenase

Myositis-specific autoantibodies

Autoantibody	Association	Percentage
Histidyl-tRNA synthetase (anti-Jo-1)	Antisynthetase syndrome Flare up in spring Epstein-Barr virus (EBV), adenovirus, and influenza infection
Chromodomain helicase DNA binding protein 4 (Mi-2)	Severe dermatomyositis rash without significant lung involvement
Signal recognition particle (anti-SRP)	Flare up in fall
Alanyl-tRNA synthetase (PL-12)	Epstein-Barr virus (EBV), adenovirus, and influenza infection
Transcriptional intermediary factor 1-gamma (TIF-1γ)	Cancer-associated myositis Juvenile dermatomyositis
Nuclear matrix protein (NXP-2)	Cancer-associated myositis Juvenile dermatomyositis
Anti-small ubiquitin-like modifier activating enzyme (anti-SAE)	Cancer-associated myositis
Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR)	Statin-associated necrotizing autoimmune myopathy (SANAM)	6%