Interstitial lung disease (ILD) is the most frequent organ involvement found in near half of myositis patients, but it reveals various clinical course and therapeutic responsiveness according to the clinical and serological subsets. Some myositis-specific autoantibodies (MSAs) are useful markers for the classification of ILD in myositis and give useful information for predicting the prognosis and determining treatment.

Anti-aminoacyl-tRNA synthetases are closely associated with a common clinical manifestation, termed ”anti-synthetase syndrome” including high prevalence of ILD. ILD in patients with anti-synthetases shows a similar clinical course with a favourable response to therapy but frequent recurrences. Therefore, the concomitant use of glucocorticoids and immunosuppressive drugs is recommended from early stage of the disease.

Anti-MDA5 antibody was reported to be associated with clinically amyopathic dermatomyositis (CADM) with rapidly progressive ILD, especially in eastern Asian population. Because of a very poor life prognosis, the intensive immunosuppressive therapy against ILD from early stage is recommended using the combination of high dose glucocorticoids, calcineurin inhibitors and intravenous cyclophosphamide. We have experienced the effectiveness of plasmapheresis in some anti-MDA-positive patients with intractable ILD, suggesting a possible pathogenicity of anti-MDA5 antibody.

Thus, ILD in myositis is dependent on the autoantibodies, therefore it is important to know the profiles of MSAs in PMDM patients. Recently, we established the ELISA systems for anti-synthetase and anti-MDA5 antibodies, which are as efficient as the standard immunoprecipitation assays. These systems enable easier and wider use in the diagnosis and therapeutic decision of patients suspected to have myositis and ILD.