Case Presentation: A 33-year-old obese woman with no significant past medical history initially presented to her primary care physician with fevers, pharyngitis, rash, malaise, and myalgias for ten days. Her rash was patchy, nonpruritic and worsened with her high spiking fevers. The rash progressed in a centrifugal pattern. She had also developed significant arthralgias in bilateral knees and ankles and edema of her hands and feet. Symptoms persisted despite Augmentin and azithromycin. When she subsequently presented to our emergency room, she had a leukocytosis with no clear source of infection, elevated troponin, and significantly elevated D-dimer, with no pulmonary embolism on CT angiography of the chest. She continued to have intermittent high fevers to 103°F, and her leukocytosis and serum ferritin continued to increase to 22K and >15K, respectively. Blood and urine cultures had no growth. She had hepatosplenomegaly on abdominal ultrasound. An extensive infectious workup including EBV and CMV PCR, HIV 1/2 antibodies, RPR, and measles was negative. Rheumatoid factor (RF) and antinuclear antibody (ANA) were negative. Given her persistent rash with high fevers, leukocytosis, elevated ferritin, no clear source of infection, and hepatosplenomegaly, rheumatology was consulted to confirm our diagnosis of Adult Onset Still’s Disease (AOSD). She received methylprednisolone 48mg IV daily for two days in the hospital with improvement of symptoms and was discharged home on Prednisone 60mg with taper.

Discussion: AOSD is a rare inflammatory disorder of unknown etiology that has been used to describe features of systemic Juvenile Inflammatory Arthritis occurring in patients older than 16 years. AOSD is a diagnosis of exclusion and features a constellation of signs and symptoms including high spiking fevers, arthralgias, and evanescent rash. Because AOSD has a heterogenous presentation, it can be difficult to identify and diagnose. Of the seven sets of diagnostic criteria proposed, the Yamaguchi Criteria is the most commonly used due to its high sensitivity. Our patient met the Yamaguchi Criteria based on the presence of fevers and leukocytosis with >80% PMNs (two major criteria) and sore throat, hepatosplenomegaly, abnormal LFTs, and negative ANA and RF (four minor criteria). Additionally, the patient had a non-pruritic maculopapular rash with centrifugal spread that worsened with fever and severe arthralgias for 12 days, both of which could qualify for major criteria had they been present for more than two weeks at the time of diagnosis. Therapy goals of treating AOSD include controlling inflammation and preventing end-organ damage and complications, such as hepatitis and joint destruction.

Conclusions: AOSD can manifest with acute, severe illness and as such, it is often first diagnosed and managed by hospitalists. This case presentation highlights the complexity of identification and diagnosis of Adult Onset Still Disease.