March 2026 Research Update

What this month added

These studies reinforced that HLH is often a reaction to an underlying trigger, and infections plus immune suppression showed up repeatedly as the setting where HLH developed. Across hospital cohorts and individual cases, viral and bacterial infections were common triggers, and coinfections were not rare. The main message is not that one infection looks the same as another, but that finding and treating the trigger was tightly linked to how the illness unfolded in the reports this month. [1] [2] [3] [4] [5]

In dengue-associated HLH, a pediatric cohort from Colombia reported a 21.1% death rate, and deaths occurred only in children who also had significant other health problems; higher bilirubin was the one lab value linked with death in that group. Viral coinfections were common, including EBV and CMV in more than one third, which matters because coinfections can complicate the clinical picture and may affect what doctors look for during evaluation. A separate single-patient dengue report described rapid improvement after corticosteroids, showing how quickly inflammation can change in some cases, although one case cannot predict what will happen for others. [1] [6]

Tuberculosis-associated HLH was described both as a 19-person adult hospital series and as a single case that initially looked like lymphoma because of necrotic lymph nodes on imaging. In the 19-person series, neurologic symptoms occurred only in disseminated (more widespread) TB, and overall mortality was 21.1%; several deaths were in people with HIV. The single-case report added a practical reminder that standard screening tests can be negative even when TB is the trigger, and tissue testing can be what confirms the diagnosis. [2] [7]

Several reports highlighted less common infectious or infection-like contexts that can still lead to HLH when inflammation escalates. A small pediatric series of visceral leishmaniasis-associated HLH reported that initial HLH-focused immunochemotherapy responses were suboptimal until the parasite was identified and treated with sodium stibogluconate, after which all 4 children had partial HLH responses. Another case described visceral leishmaniasis being found by blood PCR after the workup was initially pulled toward a suspected lymphoproliferative disorder, emphasizing how the first suspected explanation can sometimes be wrong in complex HLH. [3] [8]

Immune suppression from medicines also appeared as part of the trigger story. A kidney transplant case described EBV-associated HLH together with EBV-associated PTLD in the transplanted kidney, and HLH improved after reducing immune-suppressing drugs, with kidney function remaining stable long term despite persistent EBV DNA. A drug-safety signal analysis in glioblastoma patients reported disproportionate reporting signals for HLH and opportunistic infections when bevacizumab was combined with temozolomide, but this type of database study cannot prove cause or estimate risk. [4] [9]

One case linked HLH to an immune-stimulating antiviral medicine rather than immune suppression. A patient treated with PegIFN-alpha-2b for chronic hepatitis B developed HLH about 3 weeks after stopping therapy, improved after etoposide plus dexamethasone, and then had sequential infections identified using metagenomic testing. This adds a reminder that HLH can arise after immune system shifts in either direction, and that new infections can emerge during a complicated course. [10]

What this means for patients and caregivers

This month strengthened a practical point patients often hear: HLH is usually a sign of something else driving the immune system, especially infection or immune-system disruption. The evidence here is mostly observational studies and case reports, so it cannot tell an individual person what will happen, but it does clarify the kinds of triggers that kept appearing across different settings (dengue, TB, EBV-related illness, leishmaniasis, transplant immunosuppression, and some cancer medicines). For patients, the main near-term relevance is understanding why the workup often focuses intensely on finding a trigger, including possible coinfections, because that underlying cause can shape the next steps and the likely course. What remains uncertain is how well any one lab marker or pattern predicts outcomes across all triggers, since the studies were small and varied.

What this month added

These studies added to a consistent picture that HLH can appear alongside blood cancers, some solid tumors, or their treatments, and that this combination can strongly affect outcomes. Real-world cancer cohorts and national registries both showed that malignancy is a frequent context for adult HLH and is tied to worse survival than HLH without an identified trigger. The case reports then filled in what this can look like in real life, including diagnostic challenges and mixed responses to therapy in individual people. [11] [12] [13]

At the population level, a Danish registry study found that 46% of adult HLH cases were triggered by hematologic (blood) cancers, most commonly lymphomas, and 1-year survival was much lower in malignancy-associated HLH than in idiopathic HLH. A Polish multi-center cohort of EBV-positive NK/T-cell malignancies reported HLH in 21.7% of patients, and HLH was the strongest predictor of poorer overall survival in that group. Together, these data help explain why HLH is often discussed as a major complication when it occurs with certain cancers, even though the studies do not isolate the effect of any single treatment. [11] [12]

Several individual reports described lymphoma presenting with, complicating, or being complicated by HLH, with very different courses. One patient with primary hepatic diffuse large B-cell lymphoma (DLBCL) and secondary HLH had a complete response on follow-up imaging after chemotherapy, although significant myelosuppression required changing the regimen. Another DLBCL case described an HLH-like syndrome with rapid central nervous system progression, where the key diagnostic step was a biopsy outside the brain after PET/CT findings were not strongly positive; the patient later died after chemotherapy was declined. [13] [14]

Blood cancers other than lymphoma also appeared as HLH contexts in case reports. One report described acute erythroid leukemia with secondary HLH where remission was achieved only after switching chemotherapy, but the patient died within 3 months from bleeding and respiratory complications during a difficult course. Another described Castleman disease transforming to angioimmunoblastic T-cell lymphoma complicated by HLH, where fever and lab markers improved quickly with ruxolitinib plus dexamethasone and then ruxolitinib with CHOP, but the patient later died from a cerebrovascular event. [15] [16]

Two more reports described HLH that appeared after cancer treatment had already started. A case of Grade 3 lymphomatoid granulomatosis (a rare EBV-related disease in which immune cells grow abnormally) treated with DA-EPOCH-R chemotherapy initially showed imaging improvement, but the disease then stopped responding, was complicated by HLH, and the patient died of progressive disease. Another case described HLH during chemoradiotherapy in a patient with both DLBCL and rectal cancer, with EBV and CMV infections identified during the HLH course; despite steroids and antiviral therapy, the patient deteriorated and died. [17] [18]

What this means for patients and caregivers

For patients living with cancer, these studies add clarity that HLH is not only a separate diagnosis but can be tightly intertwined with the cancer itself or with the immune stress of treatment. The strongest evidence here comes from registries and real-world cohorts showing that malignancy is a common trigger and that survival is worse when HLH is linked to blood cancers, while the case reports illustrate how variable individual courses can be. This does not define what will happen to any one person, but it helps explain why doctors may pursue urgent evaluation for underlying lymphoma, leukemia, or viral reactivation when HLH appears. What remains uncertain is which cancer treatments best prevent or reverse HLH in each setting, because most of this month's evidence was observational or single-patient reports rather than head-to-head trials.

What this month added

This month expanded the picture of how HLH can be identified and classified, from inherited forms to hospital-based detection approaches to immune-cell patterns seen in blood. Some studies made inherited HLH feel more specific by tying symptoms to particular gene changes and functional immune tests, while another study cautioned against assuming that having several HLH-related gene variants automatically increases risk. Alongside this, EHR and immune-profiling work showed how the definition of HLH can change who gets counted as having HLH and what biologic signals may track with organ problems. [19] [20] [21] [22] [23]

On the inherited side, a neonatal HLH comparative analysis reported that familial neonatal HLH more often involved in utero symptoms, preterm birth, and family history, and had poorer overall survival than infectious neonatal HLH, while infectious cases had higher ferritin levels in the compiled data. A separate infant case report described familial HLH type 2 due to two PRF1 variants (including a newly reported A21V variant) with reduced perforin expression on testing, and the child was in remission more than a year after HLH-2004 based treatment and cord blood transplant. These reports help distinguish inherited HLH as a group where genetics and immune function testing can be central to explanation, even though each report covers only a small slice of the full spectrum. [20] [19]

Several case reports highlighted inherited immune disorders linked to HLH risk presenting in unexpected ways. An adult with Griscelli syndrome type 2 (RAB27A variants) presented primarily with neurologic symptoms and late-onset disease, and the report reclassified one variant as likely pathogenic based on family testing. A separate report described a newborn diagnosed with Griscelli syndrome type 2 (RAB27A variant) before any HLH had developed, who was referred for bone marrow transplant; her older sister, with the same silvery hair, had died of infection at 4 months without being tested. A distinct two-patient report described late-onset familial HLH type 3 (UNC13D variants) presenting as brain inflammation that looked like CLIPPERS on MRI, with neurologic outcomes after transplant that were stable in one and relapsed then improved in the other. [24] [25] [26]

In contrast to the case reports suggesting strong effects of certain gene changes, a larger genetic study found no evidence that carrying digenic or multigenic single-copy variants in HLH-related genes increases HLH risk in the populations studied. It also reported that some variants labeled as pathogenic in a database were seen in healthy adults even in two-copy form, raising the possibility that some variants may have been misclassified. For families who encounter genetic results with uncertain meaning, this kind of work matters because it pushes the field toward more careful interpretation rather than assuming risk from gene findings alone. [21]

Two pediatric hospital-based studies focused on how HLH is recognized and measured in practice. One EHR study showed that using different electronic definitions (diagnosis code, treatment plan, or meeting HLH-2004 criteria) identified very different groups of patients, and among those meeting at least 5 criteria, short-term mortality was similar whether HLH-directed therapy was given or not, while hospital stays were longer in treated patients. Another study measured immune-cell populations in the blood and found higher CD8 T cells and lower CD4 T cells and B cells in children with HLH compared with healthy controls, with different patterns linked to different organ dysfunctions. [22] [23]

What this means for patients and caregivers

These studies help explain why HLH can be hard to label with one clear boundary, especially in hospitals where inflammation and infection can resemble HLH. The genetic reports may matter now for some families because they show how gene findings can be paired with immune-function testing and clinical patterns, but the larger genetics study also adds an important caution that not every HLH-related gene variant automatically raises risk. The EHR and immune-profiling work is mainly research at this stage, but it helps clarify why two people with similar symptoms might be classified differently depending on which criteria are used, and it points toward future tools that could support earlier recognition and tracking of organ involvement. What remains uncertain is which immune-cell patterns or computable EHR definitions will prove most reliable across different hospitals and different HLH triggers.

What this month added

This month's remaining case reports showed how HLH can appear in diverse, sometimes surprising settings, including neurologic presentations, autoimmune disease, and immunotherapy. Taken together, they do not define typical outcomes, but they do widen the range of situations where HLH was recognized and confirmed. They also highlight that HLH can vary from steroid-responsive episodes to courses that remain refractory despite intensive treatment. [27] [28] [29] [30] [31]

Neurologic or neuropsychiatric symptoms were part of how HLH came to attention in more than one report. One adult with EBV-triggered secondary HLH presented with neuropsychiatric features, with HLH confirmed on bone marrow testing. A separate report described an adult with Griscelli syndrome type 2 whose HLH-associated illness had a primarily neurologic presentation, including cerebellar signs such as ataxia and nystagmus, underscoring that nervous-system symptoms can be an early clue. [27] [24]

Autoimmune and immune-dysregulation contexts were also described. A case report described macrophage activation syndrome associated HLH in a patient with myasthenia gravis, with rapid improvement after high-dose steroids followed by etoposide and sustained remission reported after discharge. This type of report mainly adds awareness that immune-driven diseases can be part of the trigger search, even when initial infection and cancer evaluations do not show a clear cause. [28]

Immune checkpoint inhibitors appeared again this month as a setting where HLH can occur as an immune-related side effect. One pembrolizumab-associated HLH case reported rapid improvement with steroid monotherapy and no HLH recurrence at 8 months, while a separate perspective article summarized published experience and proposed an approach to recognition and management, illustrated by 2 melanoma cases with differing outcomes. This combination of a single successful case plus expert opinion helps clarify the clinical suspicion pathway, but it remains early evidence rather than proof of best treatment. [30] [31]

Chronic active EBV with HLH and NK/T-cell lymphoma was described as a difficult, refractory course in a young adult despite HLH-94 chemotherapy and haploidentical transplant, with persistent NK-cell expansion and death within 1 year. This case stands in contrast to the reports with rapid improvement, underscoring that HLH outcomes can depend heavily on the underlying driver and whether it can be controlled. [29]

What this means for patients and caregivers

For patients, these reports mainly add understanding rather than changing anything immediately, because they are single cases or expert opinion. They help clarify that HLH can present with symptoms that look neurologic or psychiatric, can be linked to autoimmune immune dysregulation, and can occur as a rare complication of immunotherapy. They also show that some people improve quickly with steroids, while others have persistent disease despite transplant, which reflects differences in the underlying trigger rather than one universal HLH course. What remains uncertain is how often these rare situations occur and which treatment paths work best, because case reports cannot estimate typical risks or outcomes.