Myophaties (Myositis) Screen

Indication

Suspicion of polymyositis (PM), dermatomyositis (DM) or overlap syndrome.

Method

Immunoblot

Response

The test result is given as a numeric result for the reaction’s intensity.

Interpretation

Mi-2α and Mi-2β antibodies
Antibodies against Mi-2 are associated with classical dermatomyositis and are detected in up to 30% of the patients. Anti-Mi-2 can also be detected in a small proportion of patients with polymyositis (<10%). The Mi-2 antigen contains two chains, and patients can have antibodies against both the alpha and beta chains of the Mi-2 antigen. There is no known difference in clinical significance between antibodies directed against the two Mi-2 chains.

Ku antibodies
Anti-Ku antibodies are associated with "systemic sclerosis/polymyositis overlap syndrome", but can in some cases also be detected in other diagnoses such as SLE, Sjögren's syndrome, idiopathic pulmonary fibrosis and inflammatory myositis. Anti-Ku is often detected together with antibodies against SSA/Ro52.

The presence of anti-Ku in inflammatory muscle disease is unclear.

SRP antibodies
Anti-SRP is a strong marker for polymyositis and is associated with an aggressive lapse of necrotic myopathy and poor response to therapeutic treatment. Anti-SRP is rarely detected in dermatomyositis, and is rarely associated with interstitial lung disease. The level of anti-SRP levels correlates to disease activity. Antibodies against SRP are directed against a protein that is important for transport in the endoplasmic network. Anti-SRP has also been reported to occur in occasional cases of systemic sclerosis and rheumatoid arthritis.

Jo-1 antibodies 
Anti-Jo1 is the most common type of anti-synthetase antibodies and is detected in up to 20-30% of patients with inflammatory myositis (poly-/dermatomyositis). In 50-75% of the cases, interstitial lung disease is also seen.

PL-7 and PL-12 antibodies
Anti-PL-7 is a type of anti-synthetase antibody and can be detected in <5% of patients with inflammatory myositis (poly-/dermatomyositis). Anti-PL-7 is often associated with interstitial lung disease that may occur with or without myositis. Symptoms are similar to those seen in the presence of anti-PL-12 antibodies.

Anti-PL-12 is a type of anti-synthetase antibodies and can be detected in <5% of patients with inflammatory myositis (poly-/dermatomyositis). Anti-PL-12 is often (90%) associated with interstitial lung disease that may occur with or without myositis.

EJ antibodies
Anti-EJ is a type of anti-synthetase antibody and can be detected in <5% of the patients with inflammatory myositis (poly-/dermatomyositis).

OJ antibodies
Anti-OJ is a type of anti-synthetase antibody and can be detected in <5% of the patients with polymyositis.

PM-Scl100 and PM-Scl75 antibodies
Antibodies against the PM-Scl complex are associated with polymyositic/systemic sclerosis overlap syndrome. The antibodies are usually associated with positive ANA with nucleolar patterns. Anti-PM-Scl may be directed to different subunits in the PM-Scl complex, usually the 75 kD and 100 kD subunits included in this test. Anti-PM-Scl is often associated with Raynaud's phenomenon, arthritis, muscle aches and effects on the skin and lungs.

TIF1γ antibodies (p155/140)
Antibodies against TIF1γ (formerly known as anti-p155 / 140; the test used detects antibodies against p155 portion which corresponds to the clinically most important autoantibodies) is associated with dermatomyositis. In adult dermatomyositis (but not in children), the presence of anti-TIF1γ is strongly associated with malignancy. In children, anti-TIF1γ is associated with skin reactions (Gottron's papules, ulcerations, edema).

MDA5 antibodies (CADM140) 
Antibodies against melanoma-differentiation-associated genes 5 (anti-MDA5) occur in approximately 70% of the dermatomyositis patients where muscle weakness may be mild and CK (creatine kinase) normal (amyopathic dermatomyositis). Anti-MDA5/anti-CADM140 is strongly associated with rapidly progressive interstitial lung disease. The antibodies were directed against a 140 kD antigen, therefore the antibody is also called anti-CADM140. 

NPX2 antibodies (MJ)
Anti-NPX2, also known as anti-MJ, can be detected in approximately 20% of the children and younger adult patients with myositis, often with pronounced muscle pain (atrophy, contractures). It occurs even with calcination, ulcerations and vasculitis. Anti-NPX2 myositis often respond well to treatment and is not associated with interstitial lung disease or malignancy.

SAE1 antibodies (SUMO-1)
Antibodies against "small ubiquitin-like modifier activating enzyme" (called anti-SAE or anti-SUMO-1) can be detected in <10% of the dermatomyositis patients. The clinical picture includes Gottron's papules and heliotropic eyelid serotomy. Skin symptoms often precedes myositis as well as dysphagia. Interstitial lung disease may also occur.

SSA/Ro52 antibodies
Anti-SSA/Ro52 can often be detected in myositis with or without other myositis-associated antibodies. Anti-SSA/Ro52 is also associated with a number of other autoimmune conditions such as rheumatic diseases and autoimmune liver disease. In pregnancy, anti-SSA/Ro52 is associated with congenital AV-block / cardiac arrhythmia in the fetus. In women with known SLE/Sjögrens syndrome, the risk of this is estimated to be around 3%. The risk of mothers with these antibodies but without rheumatic disease is unknown, but is believed to be even lower. For early diagnosis of AV-block weekly monitoring of the fetal heart rhythm is recommended between 18-24 weeks of gestation.

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