Myositis -specific and -associated antibodies in neurological disorders - A retrospective study of 727 patients.

Myositis-specific antibodies (MSAs) and myositis-associated antibodies (MAAs) are assessed in clinical neurology, serving as a non-invasive tool for the differential diagnosis of autoimmune myopathies. However, the presence of MSAs and MAAs in neurological disorders remains uncertain. Retrospective analysis was conducted on 878 serum samples from the neurological laboratory of the University Hospital Tübingen, Germany. The EUROLINE Myositis Profil 3 (IgG) Line Blot was used for antibody evaluation (anti-Mi2, -Ku, -PM-Scl100, -PM-Scl75, -Jo1, -SRP, -PL7, -PL12, -EJ, -OJ, and -Ro52). Samples were categorized into 19 disease groups, with consideration for myositis-linked and non-myositis-linked diseases. Then, the distribution of positive findings and the concurrent presence of more than one MAA/MSA were analyzed. Among 727 included line blots, 84 could be assigned to myositis-linked diseases (thereof 44 positive for MAA/MSA). MAA and MSA taken together were more frequently positive for the main group of myositis-linked disease (52.4 %) compared to the non-myositis-linked group (14.6 %, overall specificity 85.4 %). However, individual antibodies were specific, ranging above 97.5 %. False positive antibody results can also occur in neurological differential diagnoses such as muscle dystrophy or cramp fasciculation syndrome. Furthermore, the concurrent presence of more than one MAA/MSA does not show a significant association with the presence of a myositis-linked disease for antibody-positive samples (p = 0.136). Testing MSA and MAA simultaneously may not be suitable as a primary screening method for myositis-linked diseases in clinical neurological groups. However, MSAs and MAAs may offer valuable diagnostic support, particularly in cases where myositis is strongly considered.

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Declaration of competing interest None of the authors has any conflict of interest to disclose.