A diagnosis of idiopathic inflammatory myopathy (IIM), or myositis, can be made through various methods including a clinical exam, thorough patient history, blood work, EMG, MRI, and often, a muscle or skin biopsy. When IIM is part of the differential diagnosis, Myositis-Specific Antibodies (MSA) should also be a part of the testing.
As the name suggests, the MSAs are specific to myositis. A physician can order the blood work for the MSA panel, however, if immune-mediated necrotizing myopathy (IMNM) is suspected the anti-HMGCR antibody must be ordered separately as it is not currently a part of the MSA panel.
Specific antibodies for Myositis patients
High-level overview of Myositis-Specific Autoantibodies
Studies have shown many myositis-specific autoantibodies (MSAs) that can be useful for the diagnoses as well as classification of idiopathic inflammatory myopathies (IIM) because they have been shown to correlate with distinct clinical phenotypes.
Anti-Jo-1, anti-PL-7, anti-PL-12, anti-EJ, anti-KS, anti-OJ, anti-Ha, and anti-Zo antibodies target aminoacyl-tRNA synthetases and represent anti-synthetase syndrome. Anti-synthetase syndrome is characterized by myositis, interstitial lung disease, arthritis, fever, Raynaud’s phenomenon, and mechanic’s hands.
Anti-Mi-2, anti-MDA5 (anti-CADM140), anti-TIF1 (anti-155/140, anti-p155), anti-NXP-2 (anti-MJ), and anti-SAE antibodies are specific for dermatomyositis. In particular, anti-MDA5 antibodies are clinically associated with amyopathic dermatomyositis developing into rapidly progressive interstitial lung disease, whereas anti-TIF1 and anti-NXP-2 antibodies are closely correlated with cancer-associated dermatomyositis in adults. In addition, anti-TIF1 and anti-NXP-2 antibodies are predominant MSAs found in juvenile dermatomyositis, and the latter was correlated with a high incidence of calcinosis. Furthermore, anti-SRP and anti-3-hydroxy-3-methylglutaryl-coenzyme A (anti-HMG-CoA) antibodies have been found in patients with immune-mediatd necrotizing myopathy (IMNM).
A recent study suggested the presence of autoantibodies to a 43-kDa muscle protein in patients with inclusion body myositis.
Although the pathogenic role of MSAs remains unknown, recent studies have shown that myositis autoantigens are expressed at high levels in regenerating muscle fibers, which may initiate or amplify autoimmune responses in iIIM.
Glossary of terms for autoantibody listing:
Below are abbreveiations used when discussing the autoantibodies.
- PM – Polymyositis
- DM – Dermatomyositis
- JDM – Juvenile Dermatomyositis
- IBM – Inclusion Body Myositis
- ILD – Interstitial Lung Disease
- CAM – Cancer-Associated Myositis
- MCTD – Mixed Connective Tissue Disease
- RP – Raynaud’s Phenomenon
- SLE – Systemic Lupus Erythematosus
- Myositis* – May be PM or DM
- SS-A – Sjogren’s syndrome A
- SSc – Systemic Sclerosis or Scleroderma
- MDA5 – Melanoma differentiation-associated gene 5
- > – more often than
Myositis-Specific Antibodies (MSA)
MSAs can assist your doctor in helping to confirm a diagnosis of certain types of myositis such as polymyositis and dermatomyositis. They are also helpful in diagnosing Antisynthetase syndrome. These antibodies also offer some insight into potential complications you may experience during the course of your disease and potential treatment options that may work best.
It is estimated that 50% of patients with polymyositis or dermatomyositis have myositis-specific antibodies, so when a clinical exam and other testing suggest the possibility of myositis, the presence of these antibodies can be supporting evidence for a diagnosis. Myositis-specific antibodies have also improved our understanding of myositis by leading to the identification of certain clinical patterns.
Anti-Jo1 (Histidyl-tRNA synthetase)
- PM, DM + ILD; Arthritis (75%), Raynaud’s Phenomenon (50%), Mechanics Hands (20%)
- Seasonal Onset Potentially: Spring
Anti-PL-7 (Threonly-tRNA synthetase)
- PM, DM + ILD; infrequent muscle involvement, severe arthritis
Anti-PL-12 (Alanyl-tRNA synthetase)
- ILD more often than myositis, pulmonary hypertension, esophageal involvement
Anti-EJ (Glycyl-tRNA synthetase)
- PM more often than DM + ILD
- ILD + PM/DM
Anti-KS (Asparaginyl-Transfer RNA Synthetase)
- ILD more often than myositis*
Anti-Zo (Phenylalanyl-tRNA synthetase)
- ILD + myositis*
Anti-Ha (Tyrosyl-tRNA synthetase)
- ILD + myositis*
Anti-SRP (SRP – signal recognition particle)
- Severe, acute, and resistant immune-mediated necrotizing myopathy (IMNM)
- Anti-SRP Syndrome: Severe weakness and functional disability
- Seasonal onset shown in studies: August and January
- High CK levels.
Anti-Mi-2 (DNA helicase)
- DM with rash more often than muscle symptoms (clinically amyopathic dermatomyositis)
Anti-HMGCR (anti 200/100)
- Necrotizing Myopathy related to statin use. Those with this antibody should not take statin drugs.
Anti-MDA5 (anti-CADM 140)
- DM: CAM, DM with rapidly progressing lung disease
- CAM in adults
- DM: CAM, DM with rapidly progressing lung disease
Myositis-Associated Autoantibodies (MAA)
Below is a listing of some of the known Myositis-Associated Antibodies (MAA). These can be found in those with myositis as well as with other autoimmune diseases such as Lupus, Scleroderma, and overlapping conditions with myositis. As more research is completed and released we will know and share more.
- PM or DM with SSc Overlap
- MCTD, overlap syndrome
- Non-U1 snRNPs
- PM or DM/SSc or SSc overlap
- Myositis* / SSc / SLE overlap
- Anti-Ro (SS-A) includes Ro60, Ro52
- Myositis often with SS or SLE, may be associated with ILD (Ro52 especially)
- Anti-56 kDa
- Myositis, often with Jo-1
- PM, ILD, RP
- Myositis, rhabdomyolysis, chronic hepatitis
- Anti-NXP-2 (Anti-MJ)
- JDM: Severe muscle atrophy, functional impairment, and calcinosis.
- Adult DM: Associated with dysphagia and soft tissue/peripheral edema
- High cancer association
- hPM51 (protein related to DNA repair)
Other Myositis related antibodies
- Anti-mitochondrial antibodies, may have cardiac involvement
- Inclusion Body Myositis
AMA Associated Myositis, Cardiac Involvement
Patients with inflammatory myopathy associated with antimitochondrial M2 antibodies (AMA) may have cardiac involvement, dropped head, and muscle atrophy. These antibodies bind to a protein in the mitochondria, the energy-producing factory of the cell. This may also be called “AMA-associated myositis.”
Heart disease may appear in the form of myocarditis (inflammation of the heart), severe arrhythmias, or cardiomyopathy (enlargement of the heart). Although the heart disease was often not recognized to be related to the myositis, treatments that suppressed the immune system led to improvements in these symptoms.
Anti-mitochondrial antibodies identify a distinct inflammatory myopathy phenotype that is frequently associated with chronic skeletal muscle disease and severe cardiac involvement. Diagnosing this early is essential for treatment.
Inclusion Body Myositis Antibodies
It has been recently discovered that some inclusion body myositis (IBM) patients may have antibodies that can help in making a correct diagnosis, along with additional testing. These antibodies are anti-cytosolic 5’ –nucleotidase 1A (anti-CN1A or anti-NT5C1A).
This autoantibody is positive in about one-half of IBM patients. A negative test does not mean a patient does not have IBM, however, a positive test makes it likely that inclusion body myositis is the correct diagnosis.
Polymyositis and Inclusion Body Myositis can appear much the same, especially at first. The NT5C1A antibody test can now help to distinguish the two as this antibody is rarely positive for those with polymyositis.
This antibody test is sometimes positive for other autoimmune diseases and is not stricly specific to IBM.
Autoantibodies for Myositis are currently undergoing more research:
Disclaimer: Research is ongoing on many of the autoantibodies listed on this page. Please note that as research continues and new evidence is found, we will try to keep this page updated. This is for informational purposes only based on information we have at the time of this writing.
“Simply Put” is a service of Myositis Support and Understanding, to provide overviews of Myositis-related medical and scientific information in understandable language.
MSU volunteers, who have no medical background, read and analyze often-complicated medical information and present it in more simplified terms so that readers have a starting point for further investigation and consultation with healthcare providers. The information provided is not meant to be medical advice of any type.