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FeedbackQualitative Immunoprecipitation / Qualitative Immunoblot / Semi-Quantitative Indirect Fluorescent Antibody (IFA)
Myositis is characterized by inflammation of the skeletal muscles involved in movement. , The detection of antibodies may help to establish a diagnosis, aid in prognosis, and support treatment decisions.
Disease Overview
Myositis may occur in a number of inflammatory myopathies, including polymyositis/antisynthetase syndrome, dermatomyositis, necrotizing autoimmune myopathy, and sporadic inclusion body myositis, as well as overlap syndromes with connective tissue diseases. , The primary symptom of all forms of myositis is progressive muscle weakness that may develop over a period of weeks, months, or years. , Other symptoms may include joint pain and fatigue. ,
Antibody testing for dermatomyositis should be considered after a standard workup for inflammatory myopathies because it may aid in distinguishing between myopathies, , which can have important implications for therapy and prognosis.
Refer to the ARUP Consult Inflammatory Myopathies – Myositis topic for more information about myositis and the typical testing strategy for inflammatory myopathies.
Test Description
This antibody panel test may be useful for the evaluation of patients with characteristic cutaneous manifestations of dermatomyositis with or without progressive proximal muscle weakness. Clinical phenotypes for specific antibody-associated inflammatory myopathies often overlap, and targeted panels allow for rapid identification of associated antibodies. Use of the most targeted panel, ie, the panel that most closely matches the patient’s complete clinical phenotype, is recommended.
| ARUP Panel to Consider | Clinical Utility | Additional Test Information |
|---|---|---|
Dermatomyositis and Polymyositis Panel 3018866 Antibodies overlap with the antibodies on this panel | May be useful for the evaluation of patients with progressive proximal muscle weakness and/or with cutaneous manifestations suggestive of dermatomyositis | Dermatomyositis and Polymyositis Panel Test Fact Sheet |
Includes antibodies that are specific to polymyositis | May be useful for the evaluation of patients with progressive proximal muscle weakness and antisynthetase syndrome | Polymyositis Panel Test Fact Sheet |
Extended Myositis Panel 3018867 Antibodies overlap with the antibodies on this panel | May be useful for the evaluation of patients with progressive proximal muscle weakness and/or other clinical findings suggestive of polymyositis/antisynthetase syndrome, dermatomyositis, necrotizing autoimmune myopathy, or overlap syndromes associated with connective tissue disease | Extended Myositis Panel Test Fact Sheet |
Interstitial Lung Disease Autoantibody Panel 3018869 Antibodies overlap with the antibodies on this panel | May be useful for the evaluation of patients with interstitial lung disease with or without other signs and symptoms of myositis | Interstitial Lung Disease Autoantibody Panel Test Fact Sheet |
Antibodies Tested
This panel detects a selection of antibodies specific to or associated with myositis. For more information about the clinical associations with each of these antibodies, visit the ARUP Consult Inflammatory Myopathies – Myositis topic.
| Myositis-Specific Antibodiesa | |
| Antibody | Method |
| MDA5 (CADM-140) Ab | Qualitative immunoblot |
| Mi-2 (nuclear helicase protein) Ab | Qualitative immunoprecipitation |
| NXP2 (nuclear matrix protein-2) Ab | Qualitative immunoblot |
| P155/140 Ab | Qualitative immunoprecipitation |
| SAE1 (SUMO activating enzyme) Ab | Qualitative immunoblot |
| TIF-1 gamma (155 kDa) Ab | Qualitative immunoblot |
| Myositis-Associated Antibodies | |
| Antinuclear Ab (ANA), Hep-2, IgGb | Semiquantitative indirect fluorescent antibody |
aMyositis-specific antibodies are generally regarded as mutually exclusive with rare exceptions. The occurrence of two or more myositis-specific antibodies should be carefully evaluated in the context of the patient’s clinical presentation. Refer to the ARUP Consult Inflammatory Myopathies – Myositis topic for more information about myositis. bThe presence of ANA is a feature of systemic autoimmune rheumatic diseases, however, ANA lacks diagnostic specificity and may occur in the general population. Positive ANA must be confirmed by more specific serologic tests. For more information, refer to the Antinuclear Antibody (ANA) With Hep-2 Substrate Test Fact Sheet. Ab, antibody; ENA, extractable nuclear antigen; IgG, immunoglobulin G; RNP, ribonucleoprotein | |
Some antibodies may be orderable separately; refer to the ARUP Laboratory Test Directory.
Test Interpretation
Results
- Positive: Antibody detected.
- Supports a clinical diagnosis of dermatomyositis and/or an overlap syndrome.
- Results for specific antibodies may be reported as low/weak positive, positive, or high/strong positive.
- Additional interpretive information for positive antibodies may be provided on the Patient Report.
- Myositis-specific antibodies are generally regarded as mutually exclusive with rare exceptions; the occurrence of two or more myositis-specific antibodies should be carefully evaluated in the context of the patient’s clinical presentation.
- Myositis-associated antibodies may be found in patients with overlap syndromes and other conditions and are generally not specific for myositis.
- Negative: Antibody not detected.
Limitations
Results are not diagnostic in the absence of other findings and should be considered in the complete clinical context.
References
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Selva-O'Callaghan A, Pinal-Fernandez I, Trallero-Araguás E, et al. Classification and management of adult inflammatory myopathies. Lancet Neurol. 2018;17(9):816-828.
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29865091
Schmidt J. Current classification and management of inflammatory myopathies. J Neuromuscul Dis. 2018;5(2):109-129.