IMMUNE SYSTEM IN MOTION: A CASE OF ADULT-ONSET STILL'S DISEASE

ABSTRACT

CASE A 23-year-old female with a history of congenital deafness and HLAB27 positivity presented for two weeks of diffuse arthralgias, fever, and nausea. She had a history of an erythematous rash around her eyes and upper chest that had resolved with prednisone;however, her other symptoms persisted. She denied known tick exposures, drug use, sick contacts, or travel, but had recently been hiking. On presentation, she was febrile to 38.8°C and tachycardic to 130 beats/min. Her labs were notable for an AST of 232 U/L, ALT of 266 U/L, LDH of 680 U/L, haptoglobin <10 mg/dL, and ferritin of 12,230 ng/mL, with no cytopenias or leukocytosis. Her CRP was 127 mg/dL and ESR was normal. Her troponin and BNP were both elevated, to 54 ng/L and 468 pg/mL respectively. ANA and RF titers was negative. Viral studies including EBV, CMV, and SARSCoV-2 as well as bacterial studies were negative. She was started on doxycycline for possible tick-borne infection, but titers returned negative. Echocardiography and chest x-ray were unremarkable. CT scan demonstrated nonspecific para-aortic and mesenteric lymphadenopathy. The patient's presentation and labs were consistent with adult-onset Still's disease (AOSD), meeting the Yamaguchi criteria for diagnosis. She was started on IV hydrocortisone and anakinra with symptomatic improvement. Her liver function testing worsened due to concerns for macrophage activation syndrome (MAS). She was treated with ruxolitinib with gradual improvement in her liver function, followed by tofacitinib. She made a full recovery on discharge. IMPACT/DISCUSSION: Due to its rarity, AOSD can be challenging to diagnose. This case highlighted the key manifestations and distinguishing characteristics of the disorder. The patient presented with fever, rash, and polyarthralgias. While the location of the rash in AOSD varies, the upper chest as seen in this case is typical. While this patient did not have cytopenia or leukocytosis, she did have elevated transaminases and a disproportionately elevated ferritin, a hallmark of AOSD. Importantly, ANA and RF titers were negative, which helps to differentiate AOSD from other autoimmune disorders. The case also demonstrated a feared complication of AOSD, MAS, a form of hemophagocytic lymphohistiocytosis that occurs in 10-15% of patients with AOSD. This case highlighted the importance of remaining vigilant for MAS, as the patient's liver function continued to decline despite symptomatic improvement. While MAS is difficult to diagnose, hyperferritinemia and pancytopenia are thought to be relatively strong indicators. CONCLUSION: AOSD is a rare and debilitating disease, with an illness script that has significant overlap with other diseases. In addition to the combination of polyarthralgias, rash, and fevers, a markedly elevated ferritin is a strong indicator of AOSD. ANA and RF titers will be negative. It is crucial to remain vigilant for complications of the disease, such as MAS.