Patient’s laboratory and clinical response to treatment. (A) Our patient’s clinical and laboratory abnormalities and how he met criteria for diagnosis of HLH noted at initial diagnosis, at diagnosis of refractory disease, and after treatment with ruxolitinib. Laboratory testing was sent at each time point; X indicates that a criterion was met. (B) Temperature curve (°C). Patient remained febrile after etoposide and dexamethasone treatment and after anakinra treatment. Patient became afebrile and has remained afebrile after ruxolitinib was administered. (C) Ferritin and C-reactive protein (CRP). Ferritin remained elevated after etoposide and dexamethasone were started and, although eventually beginning to fall, rebounded at time of diagnosis of refractory HLH. Ferritin continued to decline to the normal range after the patient received ruxolitinib. Similarly, CRP, a nonspecific marker of inflammation, was elevated at the start of treatment and began to decline after etoposide and dexamethasone were started. CRP began to rise as the patient became refractory to treatment and then declined to normal range after ruxolitinib administration. (D) Soluble IL-2 receptor. Although not elevated at initial diagnosis, soluble IL-2 receptor increased with persistent fevers and inflammation and reached a maximum level just before start of ruxolitinib. After ruxolitinib initiation, soluble IL-2 receptor levels returned to normal.