A case of anti-NPX-2 antibody-positive dermatomyositis resulting in massive haemothorax with acquired factor XIII deficiency.

Autoimmune diseases, including dermatomyositis, can be complicated by an acquired autoimmune coagulation factor XIII deficiency, which sometimes results in fatal bleeding. Here, we report the case of a young woman with anti-NPX-2 antibody-positive dermatomyositis who developed massive haemothorax with acquired factor XIII deficiency during treatment, including plasma exchange therapy. Emergency transcatheter arterial embolisation was performed and coagulation factor XIII concentrates (Fibrogammin P® 240 U/day for 5 days) were supplemented. Subsequently, the patient was discharged and managed with oral prednisolone and tacrolimus. Coagulation system test results were followed up regularly and remained within normal limits and the patient progressed without recurrence of bleeding symptoms. Coagulation factor XIII deficiency cannot be assessed without measuring coagulation factor XIII activity because common coagulation-fibrinolytic system test results are not abnormal. The measurement of factor XIII activity should be performed when autoimmune diseases are complicated by unexplained bleeding.