An atypical presentation of hemophagocytic lymphohistiocytosis secondary to toxoplasmosis in an immunocompetent 10-yearold boy

ABSTRACT

Case Report Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition that can occur as primary disorder or secondary to a variety of infections, rheumatic diseases, or malignancies. It is usually diagnosed among patients who are hospitalized with shock-like multiorgan dysfunction and unremitting fevers. It is associated with high mortality and morbidity. HLH secondary to toxoplasmosis is not uncommon in immunocompromised patients. However, it is rarely reported in immunocompetent patients. We herein, report a case of HLH triggered by toxoplasmosis in an immunocompetent patient. Case description A previously healthy 10-year-old male, who lives on a farm, presented with acute onset abdominal pain, vomiting, subjective fever, generalized myalgia, lymphadenopathy, and hepatosplenomegaly. Initial labs revealed thrombocytopenia, neutropenia, abnormal hepatic panel, and significantly elevated ferritin, which worsened upon recheck. Further workup revealed increased triglyceride and soluble IL-2 receptor and decreased fibrinogen, which confirmed the diagnosis of HLH. Toxoplasma testing showed positive IgM and IgG with low IgG avidity, indicative of a recent infection. Brain MRI and fundoscopy were unremarkable. Other infectious workup including hepatitis A, B, and C viruses, CMV, and respiratory pathogen panel including Covid-19 were negative. EBV serology was consistent with previous infection. Immunologic work up showed increased CD8 T cells and increased IgM. Treatment for HLH was not initiated since patient remained well-appearing and afebrile throughout the hospital stay. Treatment for toxoplasmosis was not indicated due to the absence of brain and retinal involvement. Subsequently, laboratory parameters started to improve on day 6 of hospitalization. The patient was discharged the following day. Five days later, platelet count, ANC, ferritin, and fibrinogen levels were normalized. Discussion Although meeting HLH-2004 diagnostic criteria, the course of illness was not typical, as this patient remained afebrile and clinically well with spontaneous recovery. This is in contrast to 95% of typical HLH cases that have high unremitting fever. The initial suspicion of HLH was low due to the atypical features. We proceeded with the HLH investigations due to hyperferritinemia on repeat testing, which has a 90% sensitivity for HLH. Soluble IL-2 receptor test further confirmed our suspicion. To our knowledge, there have been only a few pediatric case reports of HLH secondary to acquired toxoplasmosis without an underlying condition. No underlying immune deficiency disorder was found. Conclusion This case highlights the fact that toxoplasmosis can trigger HLH in immunocompetent children. Early diagnosis and prompt treatment are crucial in avoiding a fatal outcome.