Overview
Secondary hemophagocytic lymphohistiocytosis (sHLH) is a rare and severe hyperinflammatory syndrome characterized by excessive activation of the immune system leading to widespread tissue damage. Unlike primary HLH, which is often congenital, secondary HLH arises as a complication of underlying conditions such as infections, malignancies, autoimmune diseases, and metabolic disorders. The heterogeneity and rarity of secondary HLH in adults pose significant challenges in developing standardized treatment protocols and conducting large-scale clinical trials [PMID:36131317]. This guideline aims to synthesize current evidence to provide clinicians with a comprehensive understanding of the epidemiology, clinical presentation, diagnosis, management, and prognosis of secondary HLH, particularly focusing on adult populations.
Epidemiology
The epidemiology of secondary HLH in adults is marked by its rarity and variability, complicating efforts to establish robust epidemiological data. A study encompassing 259 newly diagnosed sHLH patients revealed that approximately 18.2% (47 patients) developed concomitant macrophage activation syndrome (CLS), predominantly affecting middle-aged adults with a median age of 50 years, and a male predominance (66%) [PMID:33037588]. This demographic skew suggests that middle-aged men may be at higher risk for developing severe forms of sHLH, possibly due to underlying comorbidities or hormonal factors. Additionally, pediatric cases of HLH associated with brucellosis highlight specific environmental risk factors, such as consumption of unpasteurized dairy products and close contact with livestock, indicating that certain infectious exposures can trigger HLH across different age groups [PMID:27367321]. These findings underscore the importance of considering both demographic and environmental contexts in assessing risk factors for secondary HLH.
Clinical Presentation
The clinical presentation of secondary HLH is often nonspecific but typically includes a constellation of systemic symptoms. Fever is universally present, alongside common manifestations such as malaise, myalgia, anorexia, sweating, and significant weight loss [PMID:27367321]. In a detailed study by Man et al., patients with CLS-sHLH exhibited notable laboratory abnormalities, including significantly lower albumin levels (22.3 g/L vs 39 g/L) and elevated triglyceride levels (3.17 mmol/L vs 3.02 mmol/L) compared to those without CLS, suggesting these markers may aid in early clinical suspicion and monitoring [PMID:33037588]. Furthermore, distinct cytokine profiles differentiate HLH triggered by malignancies from those secondary to infections, with malignancy-associated HLH showing markedly elevated levels of interferon-gamma (IFN-γ) and CXCL9 [PMID:33417087]. These cytokine patterns can guide targeted diagnostic and therapeutic approaches, emphasizing the need for comprehensive biomarker assessment in clinical practice.
Diagnosis
Diagnosing secondary HLH relies on fulfilling at least five of the eight modified HLH-2004 criteria, which encompass clinical and laboratory parameters such as fever, splenomegaly, cytopenias, hypertriglyceridemia or hypofibrinogenemia, elevated ferritin, increased soluble IL-2 receptor (sIL-2R), impaired natural killer (NK) cell activity, and evidence of hemophagocytosis [PMID:36131317]. Biomarker analysis plays a crucial role in early and accurate diagnosis. Ferritin, IL-18, and glycosylated ferritin have emerged as particularly useful markers, with specificities of 84%, 79%, and 71% respectively, when sensitivity is set at 85% [PMID:33417087]. Combining IL-18 with the HScore significantly enhances diagnostic specificity to 86%, maintaining 100% sensitivity, thereby offering a robust approach for clinical confirmation [PMID:33417087]. Histopathological confirmation through bone marrow examination, demonstrating hemophagocytosis, remains definitive, alongside specific diagnostic tests for underlying triggers like brucellosis, which can be identified through high-titer agglutination tests and positive cultures [PMID:27367321].
Management
The management of secondary HLH in adults often mirrors pediatric protocols, such as the HLH-94 and HLH-2004 regimens, which typically include etoposide, dexamethasone, and cyclosporine to control hyperinflammation and immune dysregulation [PMID:36131317]. However, the efficacy of these treatments can vary significantly, as evidenced by a retrospective study where only 74% of CLS-sHLH patients achieved remission post-treatment, highlighting the need for individualized management strategies [PMID:33037588]. Notably, the use of tocilizumab (TCZ), an IL-6 receptor inhibitor, has shown limited clinical benefit in adult sHLH patients despite its success in other hyperinflammatory conditions, underscoring the complexity of treating this syndrome [PMID:36131317]. Addressing underlying causes, such as targeted antibiotic therapy for brucellosis, can lead to complete recovery and normalization of blood counts within 2 to 4 weeks, emphasizing the importance of identifying and treating the primary trigger [PMID:27367321]. Clinicians must carefully weigh these treatment options, considering patient-specific factors and potential comorbidities to optimize outcomes.
Complications
Secondary HLH in adults is fraught with significant complications, particularly in elderly patients with pre-existing comorbidities. Hypoalbuminemia, often observed in CLS-sHLH patients, is significantly associated with poorer outcomes, reflecting the severity of systemic inflammation and its metabolic consequences [PMID:33037588]. Additionally, the risk of treatment-related complications, especially infections, poses a substantial clinical challenge. Immunosuppressive therapies required to manage HLH can compromise the patient's ability to fight off secondary infections, necessitating vigilant monitoring and supportive care measures [PMID:36131317]. These complications underscore the need for multidisciplinary approaches in managing secondary HLH, integrating infectious disease specialists, hematologists, and critical care physicians to mitigate risks effectively.
Prognosis & Follow-up
The prognosis of secondary HLH varies widely depending on the underlying cause, patient age, and response to treatment. Studies indicate that while some patients achieve remission with appropriate management, others may face persistent symptoms or complications, necessitating ongoing monitoring and tailored follow-up strategies [PMID:33037588]. For instance, cases linked to brucellosis generally exhibit positive outcomes with targeted antibiotic therapy, suggesting that early and accurate identification of the primary trigger can significantly influence prognosis [PMID:27367321]. Long-term follow-up is crucial for assessing recovery, managing potential late sequelae, and addressing any residual immune dysregulation. Regular clinical evaluations, laboratory monitoring, and imaging studies should be individualized based on the patient's initial response and underlying condition to ensure optimal long-term outcomes. Given the variability in treatment responses, continuous reassessment and adaptive management plans are essential in clinical practice.
References
1 Kim JY, Kim M, Park JK, Lee EB, Park JW, Hong J. Limited efficacy of tocilizumab in adult patients with secondary hemophagocytic lymphohistiocytosis: a retrospective cohort study. Orphanet journal of rare diseases 2022. link 2 Man C, Wang M, Yin G, Huang J, Cheng W, Wu X et al.. Clinical features of 47 secondary hemophagocytic lymphohistiocytosis patients complicated with capillary leak syndrome. International journal of hematology 2021. link 3 Debaugnies F, Mahadeb B, Nagant C, Meuleman N, De Bels D, Wolff F et al.. Biomarkers for Early Diagnosis of Hemophagocytic Lymphohistiocytosis in Critically Ill Patients. Journal of clinical immunology 2021. link 4 Karaman K, Akbayram S, Kaba S, Karaman S, Garipardiç M, Aydin I et al.. An analysis of children with brucellosis associated with haemophagocytic lymphohistiocytosis. Le infezioni in medicina 2016. link