An initial diagnosis of myositis is usually made from a clinical exam, blood work, EMG, MRI, and often, a muscle or skin biopsy. Many patients, depending on where you are being tested, are now also being tested for MSA’s, or Myositis-Specific antibodies.
If is often very rare to find these antibodies in patients with different muscle diseases or autoimmune diseases. They only show in those with myositis.
These antibodies, and others called Myositis-Associated antibodies (MAA), were identified several years ago and 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 would 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.
There are dozens of myositis-specific and myositis-associated antibodies identified, and researchers are continuing to find more and learn more about them. A few of the more understood are anti-aminoacyl-tRNA synthetases, anti-Signal Recognition Particle (SRP), and anti-Mi-2: chromodomain helicase DNA binding protein 4. According to several sources, Mi-2, SRP and Jo-1 are most common and may serve as markers for myositis.
Specific antibodies for Myositis patients
High-level overview of Myositis-Specific Autoantibodies
Studies have shown many myositis-specific autoantibodies (MSAs) that are useful for the diagnoses as well as classification of idiopathic inflammatory myopathies 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 necrotizing myopathy.
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 idiopathic inflammatory myopathies.
Glossary of terms for antibody listing:
- 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
- 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
- Anti-OJ (Isoleucyl-tRNA)
- 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 necrotizing myopathy
- Anti-SRP Syndrome: Severe weakness, disability
- Seasonal onset shown in studies: Onset August and January
- High CK levels. Biopsy: active myopathy with little inflammation
- Early corticosteroid treatment often improves strength
- Anti-Mi-2 (DNA helicase)
- DM with rash more often than muscle symptoms (amyopathic dermatomyositis)
- Anti-HMGCR (anti 200/100)
- Necrotizing Myopathy related to statin use but in some, statin use was not present.
- Anti-MDA5 (anti-CADM 140)
- DM: CAM, DM with rapidly progressing lung disease
- DM: CAM, DM with rapidly progressing lung disease
- Anti-MUP44 (found in some IBM patients. See other IBM info further down)
Below is a listing of some of the know Myositis-Associated Antibodies. As new research is completed we will know more about these. These are listed for informational purposes.
- 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
- 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)
AMA Associated Myositis, Cardiac Involvement
Patients with inflammatory myopathy associated with antimitochondrial antibodies (AMA) may have cardiac involvement. These antibodies bind to a protein in the mitochondria, the energy producing factory of the cell.
Heart disease was seen in 71% (only 7 patients in this study) of the patients in the study and took 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. Muscle atrophy was also seen in the majority of patients.
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. These antibodies are anti-cytosolic 5’ –nucleotidase 1A (anti-CN1A or anti-NT5C1A).
The antibody test has been shown to be positive in only about one-half of IBM patients. A negative test does not mean a patient does not have inclusion body myositis, 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 with other autoimmune diseases including dermatomyositis, systemic lupus erythematosus, and Sjogren’s syndrome. Through a patient physical exam, medical history, and other testing, it can be distinguished from 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 information 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.
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