Myopathy

Clinical information

Idiopathic inflammatory myopathies (IIM, also called myositis syndrome or myositis) are a group of systemic autoimmune rheumatic diseases characterised by chronic inflammation of the skeletal muscles with symptoms of muscle weakness or pain leading to progressive movement limitation. In many cases, other organs such as the skin, lungs and heart are also affected. The systemic nature of the disease also becomes apparent through general symptoms such as fever, tiredness and headache. Around 13% of IIM cases are associated with a malignant tumour.

Diagnosis of IIM is challenging due to the rarity of these diseases and the potential overlap with other rheumatic diseases (overlap syndromes). Especially in cases where no muscle involvement is seen at first, diagnosis usually takes several years after the onset of the first symptoms.  

IIM classification, which is based on the clinical picture, serology and the complications to be expected, has become more detailed over time. Previously, only dermatomyositis (DM) and polymyositis (PM) were distinguished. Nowadays, there are up to six subgroups, which also include inclusion body myositis (IBM), immune-mediated necrotising myopathy (IMNM), anti-synthetase syndrome (ASS) and overlap myositis (OM).

Diagnostics

As the different IIM antibodies are associated with different symptoms, organs and prognoses, they can aid differentiation of the subgroups. New diagnostic guidelines published in 2022 by the German Society for Neurology (DGN) emphasise the importance of myositis-specific (MSA) and myositis-associated (MAA) antibodies and require that laboratory results, muscle biopsies and clinical findings be considered in parallel and given equal priority in diagnostics (guidelines of the DGN on myositis syndromes, AWMF register no. 030/054, 2022 [PDF, in German]). In the 2017 classification criteria by the European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR), detection of autoantibodies, namely anti-Jo-1, has a high weighting. It is anticipated that future updates will also include the rarer myositis-specific autoantibodies thanks to better availability of test systems for routine use.  

More than 20 different antibodies have been described in IIM diagnostics, which are categorised as MSA or MAA based on whether they occur exclusively in IIM or also in other rheumatic diseases. With a prevalence of approximately 20%, anti-Jo-1 antibodies are best known and most frequently found, while most other antibodies have a prevalence in the lower single digits. MSA also usually occur isolated, which makes serology even more difficult.  

EUROIMMUN offers a comprehensive range of line blots for the detection of IIM-relevant autoantibodies. The EUROLINE profiles for myositis diagnostics allow monospecific detection of up to twenty autoantibodies in just one incubation, including – the worldwide exclusive – cN-1A for differential diagnostics of inclusion body myositis, a rare form of IIM. This allows to not only save time and money, but also provides information about the antibodies present and the associated clinical picture.  

The portfolio is complemented by IFA for ANA determination and monospecific assays (ELISA, ChLIA) for the detection of anti-Jo-1 and anti-cN-1A.

Files

Comprehensive myositis diagnostics

EUROLINE Profiles Autoimmune inflammatory myopathies

EUROLINE myositis profiles