Neonatal Hemophagocytic Lymphohistiocytosis: Scoping Review and Analysis of 205 Cases
Authors: Kranz Lincoln , Hahn Wyatt , Thompson Whitney , Hentz Roland , Kobrinsky Nathan L. , Galardy Paul J. , Greenmyer Jacob R 
Published: December 2023

Background: Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of pathologic immune activation and uncontrolled inflammation. Neonatal HLH (nHLH), defined as HLH that presents in the first month of life, is clinically devastating. nHLH is estimated to comprise 10% of familial HLH (fHLH) diagnoses. There have been few, large descriptive studies of nHLH.
Objectives: The primary objective of this study was to perform a scoping review and descriptive analysis of published cases of nHLH. The secondary objective of this study was to assess the reporting quality of published nHLH cases.
Methods: A comprehensive literature database search was performed. Cases of HLH were eligible for inclusion if clinical analysis was performed at age &lt; 30 days. As many as 70 variables were extracted from each case. Frequencies and percentages of variables reported per case in the articles included were provided. Qualitative variables were summarized by frequency and percentage. Quantitative variables which were not approximately normally distributed were summarized with median and interquartile range (IQR).
Results: 544 studies were assessed for eligibility. Studies were excluded if they did not discuss nHLH (n=280), aggregated nHLH patient data with all ages (n=83), provided insufficient detail and/or data describing nHLH (n=28), and for other reasons (n=8).205 cases of nHLH from 142 articles were included. Cases were published from 31 countries from 1985-2023.
Primary presenting features included fever (38.1%, n=67/176), organomegaly (11.9%, n=21/176) respiratory distress (11.4%, n=20/176), jaundice (4.5%, n=8/176), and signs of bleeding (3.4%, n-6/176). Symptoms began in utero in 20 patients (n=20/161). The median age of symptom onset was day of life (DOL) 3 (IQR: 0-14) (n=141). Median age at diagnosis was DOL 15 (IQR: 6-27) (n=87). The median time from initial evaluation to initiation of HLH therapy was 8 days (IQR: 3-14) (n=53).
The frequency of HLH criteria and criteria median values are summarized in Table 1. The median number of diagnostic criteria met by patients were 5/8 (IQR: 4, 6). CNS manifestations were reported in 62.7% of cases (n=64/102). Skin manifestations were reported in 75.4% of cases (n=52/69). Liver injury (67.9%, n=91/134) and/or liver failure (23.9%, n=32/134) were common. Infections were reported in 46.7% of patients (n=70/150).
Causes of nHLH included familial/inherited disease (46.8%, n=96/205), infection (26%, n=53), macrophage activation syndrome (2.9%, n=6), primary immunodeficiency (2.9%, n=6), inborn error of metabolism (2.4%, n=5), and malignancy (2%, n=4). Diagnosis was made using clinical and laboratory features (82.4%, n=169/205), gene panel (16.1%, n=33/205), sanger sequencing (1.0%, n=2/205), and ultra-rapid whole genome sequencing (0.5%, n=1/205). Genetic causes of fHLH included mutations in PRF1, STX11, STXBP2, UNC13D, NOCAR-H, and XIAP.
The majority of patients (62.7%, n=121/193) died within the period of reporting. The estimated median survival time from nHLH onset of symptoms was 83 days.
Only 4.4% (n=9/205) of studies reported complete data to calculate an H-score. Studies reported discernable values for HLH diagnostic variables at the following frequencies: temperature (71.7%), organomegaly (82.9%), hemoglobin (69.3%), thrombocytopenia (82.4%), neutrophils (55.1%), fibrinogen (64.4%), triglycerides (5.5%), hemophagocytosis (73.2%), ferritin (71.2%), low/absent NK cell activity (33.2%), and sIL2R (29.3%). Other clinically relevant variables such as the presence or absence of skin manifestations (33.7%), and CNS manifestations (49.8%) frequently went unreported. There were many cases that made a categorical description of a lab value (e.g., thrombocytopenia) without providing an absolute value (e.g., platelets level).
Conclusions: This is the largest aggregated study of nHLH presentations, diagnostic criteria, clinical trajectory, and etiologic diagnoses. Neurologic, dermatologic, and hepatic manifestations occur in the neonatal population. Current reports of nHLH suggest a grim prognosis. Future publications containing data on nHLH should report all clinically relevant variables. Studies looking at multiple patients in aggregate should provide supplemental information with detailed nHLH cases.