Evaluation of Presenting Symptoms in Pediatric Patients with Hemophagocytic Lymphohistiocytosis (HLH) Versus HLH Mimics

Background and Purpose Hemophagocytic lymphohistiocytosis (HLH) is a severe hyperinflammatory syndrome characterized by a hyperactive but ineffective immune response, resulting in excessive cellular proliferation and cytokine secretion. This causes end-organ damage that is typically fatal without immunosuppressive therapy. Multiple disease processes share clinical and laboratory features with HLH, which contributes to diagnostic uncertainty and treatment delays. We sought to determine whether HLH and these disease mimics demonstrate differences in presenting symptomatology that can aid in tailoring a differential diagnosis. Methods We queried the UCSF Electronic Medical Record Search Engine using the terms “hemophagocytic lymphohistiocytosis” and the related disease process “macrophage activation syndrome” and filtered results to include 635 previously healthy pediatric patients. Patients were subdivided into 68 patients with a diagnosis of HLH (HLH-diagnosed), defined by the presence of the ICD-10 code, and 567 patients in whom HLH was considered on the differential diagnosis prior to assignment of an alternate diagnosis (HLH-considered). Presenting symptoms were ascertained through review of the admission note. Fischer’s exact test was used to compare frequencies of presenting symptoms between groups. False discovery rate (FDR) correction was used to account for multiple hypothesis testing. Results The most common primary discharge diagnoses in the HLH-considered group included rheumatologic diseases (31%), infections (29%), malignancies (12%), and fever of unknown origin (11%). We identified 64 distinct presenting symptoms across the cohort. The five most common symptoms in each group were identical between the two groups and included fever (63% and 63%, respectively), rash (31% and 24%), emesis (25% and 21%), fatigue (25% and 27%), and anorexia (18% and 22%). Of the 64 presenting symptoms identified in this cohort, none demonstrated statistically significant differences in frequency between the two groups. Conclusion HLH and its disease mimics, including rheumatologic diseases, infections, and malignancies, share overlapping symptom profiles that preclude prioritization of a differential diagnosis in the absence of additional diagnostic testing. Clinicians should therefore maintain a low threshold for including HLH on the differential diagnosis in patients presenting with these common symptoms.