Myositis is a striated muscle inflammatory disease that may be hereditary or triggered by infection, exposure to specific toxins, or immune system dysregulation. Autoimmune myositis (idiopathic inflammatory myopathies) are systemic autoimmune diseases characterised by inflammation of the skeletal muscle, pronounced pain in the proximal and symmetric musculature and muscle weakness.
These disorders include adult polymyositis (approx. 30%), adult dermatomyositis (approx. 30%), paraneoplastic polymyositis, juvenile myositis/dermatomyositis with associated vasculitis (approx.7%) and myositis associated with autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus or mixed connective tissue disease (MCTD). Rarer forms include granulomatous myositis, eosinophilic myositis, focal myositis and inclusion body myositis (approx. 20%).
The detection of myositis-associated autoantibodies is crucial for the diagnosis of dermatomyositis and to evaluate disease progression and disease therapy.
Autoantibodies against isoforms Mi-2α (CHD3) and Mi-2β (CHD4) of Mi-2 are highly specific for myositis, particularly for dermatomyositis (DM). These antibodies are present in approximately 15–30% of DM patients and in 8–12% of those with idiopathic myositis. Some anti-Mi-2–positive patients present with polymyositis and, in rare cases, inclusion body myositis. Anti-Mi-2 antibodies are often detectable in the early stages of the disease: in these cases, the clinical course of DM (including juvenile forms) is generally favourable. However, anti-Mi-2 positive DM (most frequently anti-Mi-2β) may also be associated with malignancy, such as colon or breast carcinoma.
The serodiagnostic significance of autoantibodies against Mi-2α (one of the two isoforms of Mi-2) is similar to that of anti-Mi-2 antibodies, with a prevalence of about 20% in dermatomyositis.
Anti-Mi-2β antibodies (the predominant isoform) are more frequently detected in DM associated with malignancies (e.g., colon or breast cancer).
Serum, EDTA plasma, heparin plasma, citrate plasma
Immunoblot
Fasting for at least 8-12 hours before sampling
Refer to the Health Service Charter to check storage conditions
+2/+8°C
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