Adult-Onset Still's Disease Causing Aortitis Diagnosed Through the Investigation of Inflammatory Anemia in a Chronic Pseudogout Patient.

Adult-onset Still's disease (AOSD) is a rare systemic autoinflammatory disorder that can present with fever, arthritis, and systemic inflammation, often complicating underlying chronic conditions. This report describes the case of a 71-year-old male patient with chronic kidney disease-related renal anemia and pseudogout (calcium pyrophosphate deposition disease (CPPD)) treated on an outpatient basis. The patient presented to our hospital with rectal bleeding lasting for two to three weeks, leading to the identification of rapidly progressing anemia through blood tests. He was hospitalized for further investigation of acute anemia and received a packed red blood cell transfusion. However, no definitive findings were obtained, and he was discharged with symptomatic treatment. Subsequently, the patient developed abdominal pain and aortic wall thickening, leading to hospitalization at a higher-level hospital. No definitive diagnosis was made, and the symptoms improved spontaneously. It was initially suspected to be inflammation due to pseudogout. While continuing outpatient treatment at our hospital, the patient developed elevated liver enzymes, increased neutrophil counts, elevated ferritin, and polyarthritis. Given the constellation of findings, AOSD was diagnosed, which was likely the underlying driver of inflammation and anemia in this case. Treatment with prednisolone and an interleukin-6 inhibitor led to symptom relief and improvement in blood test results. This case highlights the diagnostic challenges of AOSD, particularly its rare onset in elderly patients and its potential to mimic other chronic inflammatory conditions such as pseudogout. It also underscores the importance of considering AOSD in elderly patients with acute anemia and the need for accurate and prompt treatment.