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	Antigen	Association	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	20-25%
	Anti-PL-7	Threonyl-tRNA synthetase
	Anti PL-12	Alanyl-tRNA synthetase	Epstein-Barr virus (EBV), adenovirus, and influenza infection
		Alanyl-tRNA
	Anti-OJ	Isoleucyl-tRNA synthetase
	Anti-EJ	Glycyl-tRNA synthetase
	Anti Mi-2	Chromodomain helicase DNA binding protein 4	Dermatomyositis rash without significant lung involvement Acute but mild onset Good prognosis	5-10%
	Anti-SRP	Signal recognition particle	Cardiac involvement and myalgias Flare up in fall Very acute and severe onset Poor response to treatment Very poor prognosis	<5%
	Anti TIF-1γ antibody	Transcriptional intermediary factor 1-gamma	Cancer-associated myositis Juvenile dermatomyositis
	Anti NXP-2 antibody	Nuclear matrix protein	Cancer-associated myositis Juvenile dermatomyositis
	Anti-SAE antibody	Anti-small ubiquitin-like modifier activating enzyme	Cancer-associated myositis
	Anti HMGCR antibody	3-hydroxy-3-methylglutaryl-coenzyme A reductase	Statin-associated necrotizing autoimmune myopathy (SANAM)	6%
Others	Anti-FER	Elongation factor 1 alpha
	Anti-KJ	Unidentified cytoplasmic protein
	Anti-MAS	Unidentified cytoplasmic RNA