Other iatrogenic immunodeficiency-associated lymphoproliferative disorders after multidrug immunosuppressive therapy for anti-melanoma differentiation association gene 5 antibody-positive dermatomyositis: a case report.

Although other iatrogenic immunodeficiency-associated lymphoproliferative disorders (OIIA-LPDs) are rare, they are important adverse effects of immunosuppressive therapies. Even though anti-melanoma differentiation association gene 5 (MDA5) antibody-positive dermatomyositis requires multidrug immunosuppressive therapy for interstitial pneumonia control, OIIA-LPD has rarely been reported. Moreover, central nervous system (CNS) OIIA-LPD has never been documented. Here, we report a case of CNS OIIA-LPD that may have been caused by treatment for MDA5 antibody-positive dermatomyositis. A 53-year-old woman was diagnosed with MDA5 dermatomyositis and treated for rapidly progressive interstitial lung disease using multidrug immunosuppressive therapy with prednisolone (PSL), tacrolimus, and intravenous cyclophosphamide pulse therapy. Seven months after treatment initiation, vomiting led to the discovery of a cerebellar tumour. The cerebellar tumour was histologically Epstein-Barr virus (EBV)-encoded small RNA-positive diffuse large B-cell lymphoma, with EBV-DNA being positive in the blood. The patient was diagnosed with OIIA-LPDs due to EBV reactivation. Chemotherapy, including high-dose methotrexate (MTX) and rituximab, prevented tumour recurrence without exacerbating interstitial lung disease. This is the first reported case of CNS OIIA-LPD with multidrug immunosuppression in a patient with MDA5 dermatomyositis. Chemotherapy, including high-dose MTX and rituximab, can be used for central OIIA-LPD without aggravating settled interstitial lung disease. The activity of MDA5 dermatomyositis during OIIA-LPD treatment may be managed with low-dose PSL.