Comparison of the clinical features and outcome of children with hemophagocytic lymphohistiocytosis (HLH) secondary to visceral leishmaniasis and primary HLH: a single-center study

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of excessive inflammation and tissue destruction due to abnormal immune activation. The absence of normal downregulation by activated macrophages and lymphocytes is possibly the cause of hyper inflammation and dysregulated immune state [1]. Infants are most commonly affected, with the highest incidence in those younger than 3 months [2].

HLH presents as a febrile illness associated with multiple organ involvement. Thus, initial signs and symptoms of HLH can mimic common infections, fever of unknown origin, hepatitis, or encephalitis [3]. Therefore, the diagnosis of HLH is primarily based on fulfilling at least 5 out of 8 criteria based on the published diagnostic criteria used in the HLH-2004 trial [4].. Similarly, homozygosity or compound heterozygosity for verified HLH-associated mutations will confirm the diagnosis [5]. Moreover, a scoring system has been developed to generate a diagnostic score referred to as “HScore,” which estimates the probability of HLH (Table 1). A score higher than 169 was shown to predict the risk of HLH with 93% sensitivity and 86% specificity [6].

On the other hand, secondary (sporadic, acquired) HLH is generally used to describe patients without a known familial mutation who typically have a clear trigger for developing HLH. It usually follows an infectious disease caused by organisms, including Epstein-Barr virus (EBV), cytomegalovirus (CMV), hepatitis viruses, varicella infection, leishmania, Mycobacterium tuberculosis, among many others. Moreover, autoimmune and rheumatologic disorders, malignancies, and metabolic disorders may trigger the cytokine storm [7].

A few small case series of primary or secondary HLH have been reported in Iran [8‐10]. Additionally, despite a high prevalence of Visceral leishmaniasis (VL) in Southern Iran [11], there are few reports of VL-associated HLH in our region [12, 13]. Therefore, in this prospective study, we aimed to describe the clinical and laboratory findings and the outcome of children diagnosed with VL-associated HLH during a 4-year follow-up period compared to patients with primary HLH.

The current study represents the first study on HLH patients in a large referral oncology center in Southern Iran. It is also one of the most extensive case series of secondary HLH associated with VL. It was reported that VL is associated with about 2% of all cases of HLH [16]. However, we encountered a much higher prevalence due to VL’s high endemicity in Southern Iran, where this study was undertaken. It is good to know that Fars province is one of the central endemic regions of visceral leishmaniasis in southern Iran, with an estimated incidence rate of 0.01/10,000 in 2015 [11]. A recent meta-analysis reported a pooled prevalence of 2.1% (95% CI 1.4–2.8%) of VL in Southern Iran [17]. The first report of a benign hemophagocytic syndrome associated with VL in our region was published by Kumar et al. in 1994 [12]. Mokhtari and Kumar reported the first case series of VL-associated HLH among 13 patients and described their bone marrow characteristics. Hypercellular marrow with erythroid hyperplasia, megaloblastic changes, foamy macrophages, activated macrophages with cytoplasmic vacuoles and elongated cytoplasmic process, intra- and extracellular amastigotes, cytoplasmic fragments (blue bodies), plasma cells with inclusions and hemophagocytic cells, in addition to Leishman bodies (amastigotes) were the most common microscopic findings of the studied patients. The most common hematological abnormalities were anemia (88.8%), thrombocytopenia (50%,) and pancytopenia (55.5%) [13].

The clinical sign and symptoms and laboratory parameters in HLH associated with VL were very similar to primary HLH. Fever and splenomegaly were the most consistent presenting signs and symptoms detected in nearly all patients. Serum ferritin at diagnosis was higher than 900 ng/ml in all patients, and about 30% of them had extreme hyperferritinemia (> 10,000 ng/ml). However, it did not correlate with disease severity or adverse outcomes such as death or relapse. Allen et al. reported that ferritin level over 10,000 ng/ml was 90% sensitive and 96% specific for HLH [18].

On the other hand, a recent review concluded that HLH is a rare cause of extreme hyperferritinemia, and more common causes such as liver disease and malignancies should be ruled out first [19]. Since timely diagnosis and treatment are directly related to disease outcome, high serum ferritin should raise suspicion to HLH diagnosis if other criteria are met, especially in critically ill patients.

Patients with VL-associated HLH experienced higher serum ferritin and ESR. Though the underlying infection may be a simple explanation, enhanced ferroportin-mediated iron efflux due to overexpression of growth differentiation factor 15 may play a role [20]. On the other hand, primary HLH was associated with more severe thrombocytopenia, higher ALT, and worse outcome than secondary HLH. Koh et al. reported that splenomegaly, bicytopenia, Hb < 9 g/dL, and platelets < 100,000/μl were more frequently encountered in patients with primary HLH. They also reported a lower 5-yr OS in primary HLH compared to secondary HLH [21]. Some of the mentioned features, such as bicytopenia and thrombocytopenia, can be regarded as markers of disease severity, directly linked to poor survival. We came across a similar result in which thrombocytopenia served as an independent risk factor of death, especially in patients with primary HLH.

Nearly 40% of our patients had evidence of CNS involvement. The rate of CNS involvement in HLH varies in different studies ranging from 18 to 73% [22]. Some reported previously that patients with CNS disease had lower ferritin, AST, and ALT than those without CNS involvement [23]. We did not find such an association in our patients except that children younger than 2 years had more than a 6-fold higher chance of CNS disease than older patients. Moreover, bicytopenia decreased the probability of CNS involvement by 93%.

Many reports are indicating that CNS involvement might be associated with worse outcomes (19). Although the overall mortality rate was higher in those with CNS events, this association was not shown in multivariable analysis. It is generally agreed that CNS involvement poses a higher risk of relapse unless hematopoietic stem cell transplantation (HSCT) is undergone early after starting systemic therapy [22].

HScore had a good correlation with HLH-2004 criteria for the diagnosis of HLH in our study. It was reported that HScore carries a diagnostic sensitivity of 90% and specificity of 79% for HLH [6]. A cutoff of 169 had 93% sensitivity and 86% specificity for HLH [24]. Similarly, more than 90% of our confirmed cases of HLH had HScore ≥169. Given the unavailability of sCD25 and natural killer (NK) cell activity in some centers, HScore can be utilized to make early diagnosis and treatment in case of incomplete criteria.

The treatment response was 55% in our study cohort with a 3-yr OS rate of 36%. It was much lower in patients with primary HLH than secondary HLH (24% vs. 100%). All patients with VL-associated HLH were successfully treated with liposomal amphotericin. Nobody needed to be treated with etoposide or cyclosporine. Dexamethasone was initially started in a few patients with severe disease but was tapered and discontinued after a few weeks. The outcome was excellent, with no report of death or HLH relapse during the 40 months follow-up. Targeted treatment of the etiologic pathogen usually is the only treatment strategy recommended in secondary infection-associated HLH such as brucella and leishmania. Specific antimicrobial therapy usually is associated with complete recovery in most cases [25‐31].

High-dose intravenous gamma-globulin (IVIG) has been used successfully in viral-associated hemophagocytic syndrome [32]; however, none of our cases were treated with IVIG.

Platelet count less than 100,000/μl was independently associated with more than four times the increased risk of death in our patients with primary HLH. The outcome of patients with HLH and associated prognostic factors differ among different studies. A recent study in Japan reported a much better outcome in their patients with a 3-yr OS rate of 74% [33]. Koh et al. reported a 5-yr OS rate of 68% in their study cohort, which was worse (38%) in primary HLH patients. They concluded that lower age at diagnosis, severe transaminasemia, and coagulation abnormality were independent risk factors of survival [21]. In other studies, decreased serum albumin level, LDH ≥ 3707 U/L, IL-10 ≥ 456 pg/ml, neutrophil count < 500/μl, and total bilirubin > 2× normal upper limit was associated with a higher mortality rate [34‐36].

Our study faced some limitations. Firstly, some specific laboratory tests, such as NK cell function, were unavailable in our center. Besides, sCD25 was measured in a portion of our patients since it was available in our center in 2017. These tests’ unavailability might lead to a delayed diagnosis and poor outcome, evident as a lower 3-yr OS rate in our study cohort than many other reports.

VL is a potential source of secondary HLH in regions with high endemicity. The main clinical findings and complications such as CNS involvement are the same as primary HLH. It is associated with higher serum ferritin and ESR but a lower incidence of thrombocytopenia and transaminitis than primary HLH. Treatment of the underlying disease in VL-associated HLH is sufficient in most cases, with no need to start etoposide-based chemotherapy. The prognosis is excellent, with no reported death or recurrence of disease in our case series.