A Case of Adult-Onset Still's Disease Diagnosed Following Treatment for Scrub Typhus.

A 28-year-old woman, previously diagnosed with seronegative rheumatoid arthritis, was admitted with fever, vomiting, and diarrhea. She developed septic shock with disseminated intravascular coagulation and was treated with antibiotics, noradrenaline, prednisolone, and thrombomodulin. On day 3, a rash appeared, and polymerase chain reaction detected Orientia tsutsugamushi deoxyribonucleic acid, thus confirming the diagnosis of scrub typhus. Her symptoms resolved after minocycline treatment. After tapering the prednisolone, fever, rash, and arthralgia recurred. Laboratory tests revealed elevated ferritin and interleukin-18 levels. After excluding other causes, adult-onset Still's disease (AOSD) was diagnosed in this patient. The patient exhibited a rapid improvement following tocilizumab treatment. Scrub typhus and AOSD share overlapping features that complicate diagnosis.