Although pregnancy is an important risk factor for autoimmune rheumatic diseases, little is known regarding the association between pregnancy and dermatomyositis (DM) or polymyositis (PM). Herein, we present two patients with DM that developed during the perinatal period. The first patient was positive for anti-aminoacyl synthetase (ARS) antibody and developed DM in the 14th week of pregnancy. Despite treatment, her foetus died of intrauterine growth restriction in the 27th week. The second patient was positive for anti-melanoma differentiation-associated gene 5 (MDA-5) antibody and developed DM 1 week after miscarriage at 9 weeks of gestation. The patient developed severe interstitial pneumonia, and intensive therapy including tofacitinib and rituximab administration was required. Our cases and a literature review revealed that various myositis-specific autoantibodies, including anti-ARS, anti-Mi-2, anti-TIF-1γ, and anti-MDA-5, are associated with DM and PM triggered by pregnancy. We also found that delay in commencing treatment in case of active disease including myositis and interstitial pneumonia, and poor response to corticosteroids were related to poor foetal outcomes in DM and PM. Although rare in pregnant women, it is critical to consider the possibility of DM and PM in patients presenting with rash, fever, weakness, and cough, and testing for myositis-specific autoantibodies is recommended.
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