A Case of Macrophage Activation Syndrome With Elderly Onset Still's Disease Under Tocilizumab Treatment.

Adult-onset Still's disease in older adults is referred to as elderly onset Still's disease (EOSD). Few cases of tocilizumab (TCZ) use for EOSD management have been reported. Here, we report the case of an 87-year-old Japanese woman with EOSD who was not previously taking any medication. She had fatigue, sore throat, and loss of appetite for several days and gradually experienced difficulty walking. On examination, she was found to have a fever and erythema on the buttocks and extremities. Laboratory tests revealed leukocytosis with neutrophil predominance, elevated C-reactive protein (CRP) levels, and hyperferritinemia. A contrast-enhanced computed tomography scan of the chest to the abdomen showed no abnormalities. Antimicrobial therapy was initiated; however, the fever did not resolve. On day seven, 40 mg/day prednisolone (PDN) was started for EOSD in the absence of an obvious infection or a malignancy. On day 20, the fever recurred, and the patient was started on intravenous methylprednisolone (mPDN) half-pulse therapy (500 mg/day for three days). The fever resolved, and the CRP level decreased to 1 mg/dL but did not return to normal. On day 35, the fever recurred; therefore, 320 mg of TCZ was injected intravenously, and the PDN was tapered. On day 43, the patient tested positive for cytomegalovirus (CMV) antigenemia and improved on ganciclovir. On day 70, the patient developed fever, decreased white blood cell (WBC) and hemoglobin (Hb) levels, high lactate dehydrogenase (LDH) levels, hyperferritinemia, and elevated liver enzymes. Macrophage activation syndrome (MAS) was diagnosed due to hemophagocytosis on bone marrow examination. The patient was started on pulse therapy with glucocorticosteroids and cyclosporine. The patient's fever decreased, and her WBC count and LDH level normalized. The patient continued rehabilitation for muscle weakness due to prolonged hospitalization and high-dose steroid use and was discharged from the hospital on day 150. The findings in this case suggest that the use of TCZ during the remission induction phase of EOSD may lead to MAS.