The early negative bronchoscopy lowered the possibility of an infection as the etiology of the clinical presentation and narrowed the hyperferritinemia differential diagnosis. Hyperferritinemia has a sensitivity and specificity of > 90% for diagnosis when above 10,000 ng/dL in the pediatric population.7 This is not the case in adults. Hyperferritinemia is a marker of different inflammatory responses, such as histoplasmosis infection, malignancy, or iron overload rather than an isolated diagnostic tool for HLH.8 It has been reported that CD25 levels less than the diagnostic threshold of 2400 U/mL have a 100% sensitivity for the diagnosis and therefore can rule out the diagnosis. When this is taken into consideration, it can be concluded that CD25 level is a better diagnostic tool when compared with ferritin, but its main limitation is its lack of widespread availability.9 Still, there is a limited number of pathologies that are associated with marked hyperferritinemia, specifically using thresholds of more than 6000 ng/dL.10 Taking into consideration the high mortality of untreated HLH, isolated hyperferritinemia still warrants HLH workup to aggressively pursue the diagnosis and improve outcomes.
The goal of therapy in HLH is prompt inactivation of the dysregulated inflammation with aggressive immunosuppression. In our deteriorating patient, the treatment was started with only 4 of the 8 HLH-2004 diagnostic criteria being met. As per the 2018 Histiocyte Society consensus statement, the decision to start the HLH-94 treatment relies on not only the HLH-2004 diagnostic criteria, but also the patient’s clinical evolution.11 In 1994 the Histiocyte Society also published a treatment protocol termed HLH-94. A Korean retrospective study demonstrated that this protocol led to a 5-year survival rate of 60 to 80% depending on the HLH trigger and response to initial treatment.12 The protocol consists of etoposide at 150 mg/m2, 2 weekly doses in the first 2 weeks and then 1 dose weekly for the next 6 weeks. Dexamethasone is the steroid of choice as it readily crosses the blood-brain barrier. Its dosage consists of 10 mg/m2 for the first 2 weeks and then it is halved every 2 weeks until the eighth week of treatment. A slow taper follows to avoid adrenal insufficiency. Once 8 weeks of treatment have been completed, cyclosporine is added to a goal trough of 200 mcg/dL. If there is central nervous system (CNS) involvement, early aggressive treatment with intrathecal methotrexate is indicated if no improvement is noted during initial therapy.11
In 2004 the Histiocyte Society restructured the HLH-94 treatment protocol with the aim of presenting a more aggressive treatment strategy. The protocol added cyclosporine to the initial induction therapy, rather than later in the ninth week as HLH-94. Neither the use of cyclosporine nor the HLH-2004 have been demonstrated to be superior to the use of etoposide and dexamethasone alone or in the HLH-94 protocol, respectively.13 Cyclosporine is associated with adverse effects (AEs) and may have many contraindications in the acute phase of the disease. Therefore, the HLH-94 protocol is still the recommended regimen.11
To assess adequate clinical response, several clinical and laboratory parameters are followed. Clinically, resolution of fever, improvement in hepatosplenomegaly, lymphadenopathy, and mental status can be useful. Laboratories can be used to assess improvement from organ specific damage such as hepatic involvement or cytopenia. The limitation of these diagnostic studies is that they could falsely suggest an inadequate response to treatment due to concomitant infection or medication AEs. Other markers such as ferritin levels, CD25, and NK cell activity levels are more specific to HLH. Out of them, a decreasing ferritin level has the needed specificity and widespread availability for repeated assessment. On the other hand, both CD25 and NK cell activity are readily available only in specialized centers. An initial high ferritin level is a marker for a poor prognosis, and the rate of decline correlates with mortality. Studies have demonstrated that persistently elevated ferritin levels after treatment initiation are associated with worse outcomes.14,15
Several salvage treatments have been identified in recalcitrant or relapsing disease. In general, chemotherapy needs to be intensified, either by returning to the initial high dosage if recurrence occurs in the weaning phase of treatment or adding other agents if no response was initially achieved. Emapalumab, an interferon γ antibody, was approved by the US Food and Drug Administration for the treatment of intractable HLH after it demonstrated that when added to dexamethasone, it lead to treatment response in 17 out of 27 pediatric patients, with a relatively safe AE profile.16 The goal of intensifying chemotherapy is to have the patient tolerate allogenic stem cell transplant, which is clinically indicated in familial HLH, malignancy induced HLH, and recalcitrant cases. In patients who undergo hematopoietic cell transplantation (HCT) there is a tendency to increase survival to 66% at 5 years.12
Conclusions
HLH is a rare and deadly disease increasingly more present in adults. Our patient who initially presented with a sepsis diagnosis was suspected of having a hematologic etiology for his clinical findings due to markedly elevated ferritin levels. In our patient, the HLH-94 treatment protocol was used, yielding favorable results. Given the lack of specific scientific data backing updated protocols such as HLH-2004 and a comparatively favorable safety profile, current guidelines still recommend using the HLH-94 treatment protocol. Decreasing ferritin levels may be used in conjunction with clinical improvement to demonstrate therapeutic response. Persistence of disease despite standard treatment may warrant novel therapies, such as emapalumab or HCT. Physicians need to be wary of an HLH diagnosis as early identification and treatment may improve its otherwise grim prognosis.
