Haemophagocytic lymphohistiocytosis in pregnancy

Abstract

Haemophagocytic lymphohistiocytosis is a life-threatening systemic inflammatory syndrome defined by persistent fever, cytopenia and multi-organ dysfunction. Primary haemophagocytic lymphohistiocytosis classically presents in childhood as a result of genetically abnormal perforin or inflammasome function, leading to the aberrant release of pro-inflammatory cytokines causing a hyperinflammatory state. Secondary haemophagocytic lymphohistiocytosis is an acquired phenomenon occurring at any age as a result of immune dysregulation to a specific trigger such as infection, haematological malignancy or autoimmune disease. Secondary haemophagocytic lymphohistiocytosis occurring in the pregnant woman represents a diagnostic challenge and carries a significant mortality. This has led to its first inclusion in the fourth Mothers and Babies: Reducing Risk through Audits and Confidential Enquiries across the United Kingdom annual maternal report in 2017. This article presents an overview of haemophagocytic lymphohistiocytosis, reviews the literature on haemophagocytic lymphohistiocytosis in pregnancy, suggests diagnostic pathways and explores the safety and efficacy of existing and potential treatment strategies for haemophagocytic lymphohistiocytosis occurring during pregnancy.

Introduction

Haemophagocytic lymphohistiocytosis (HLH) is a life-threatening systemic inflammatory syndrome defined by persistent fever, cytopaenia and multi-organ dysfunction. The terms ‘haemophagocytic syndrome’ and ‘macrophage activation syndrome’ may also be used – the latter particularly in the context of autoimmune disease. ¹

HLH is classically divided into two categories; familial or primary HLH (pHLH), which most commonly presents in childhood and is caused by abnormal function of perforin and the inflammasome, leading to the aberrant release of pro-inflammatory cytokines. ² The second and more common form of HLH is known as secondary HLH (sHLH). This is an acquired phenomenon occurring at any age as a result of immune dysregulation to a specific trigger in the context of reduced, rather than absent, cytolytic protein function. ³ Although pHLH may present in adolescents and young adults, sHLH is by far the most prevalent subtype in women of child-bearing age. However, the distinction between genetic mutations resulting in pHLH and the possible aetiologies of sHLH is likely to be an over-simplification; heterozygous perforin pathway mutations have been described in those with sHLH, particularly in Epstein-Barr virus-(EBV) driven adult-onset sHLH, as well as other mutations in pathways leading to hyperinflammation such as NLRC4 mutations impairing inflammasome activity and SH2P1A mutations leading to impaired viral response. ²

Typically, there is a delay in the diagnosis of HLH; in part due to the similarity in presentation to sepsis and other causes of multiorgan failure. ⁴ Common triggers of sHLH include infection, autoimmune conditions and malignancy (Table 1). ⁵ Secondary HLH is challenging to diagnose and it is also challenging to treat. Multidisciplinary discussion is best sought early given the associated high mortality. The Histiocytosis UK Haemophagocytosis Across Specialty Collaboration (HASC) is a national initiative to create local and regional multidisciplinary teams to aid in the management of these women to improve outcomes.^6–8 However, alerting the local and regional specialist teams relies on the treating clinicians being vigilant to the possibility of the diagnosis and this is a challenge due to its rarity.

Table 1.

Causes of HLH.^2,4,5

Causes of HLH
Primary mutations
Defects in cytolytic function:
PRF1 (10q21-22), UNC13D (17q2), STX11 (6q24), STXBP2 (19p13), RAB27A (15q21), LYST (1q42-43), SH2D1A (Xq24-25)
Defects in inflammasome regulation:
BIRC4 (Xq25), NLRC4 (2p22.3)
Secondary aetiologies
Infections:
Viruses – EBV, CMV, HSV, HHV-6 and -8, VZV, hepatitis, HIV, parvovirus B19, influenza A and B, adenovirus, enterovirus, dengue, Ebola and others
Bacteria – Mycobacteria spp., Rickettsia spp., Staphylococcus spp., Escherichia coli, Legionella spp. and others
Parasites – Leishmania spp., Plasmodium spp., Toxoplasma spp. and others
Fungi – Aspergillus spp., Candida spp., Histoplasma spp., Pneumocystis jiroveci and others
Autoimmune conditions:
SLE, sJIA, AOSD, RA, systemic vasculitides, periodic fever syndromes, IBD and others
Malignancy:
Haematological – T-cell, NK-cell, B-cell or Hodgkin’s lymphoma, leukaemia and others
Solid organ tumours
Miscellaneous:
Transplantation – Solid organ or HSCT
Iatrogenic – Immunosuppression, vaccination, surgery, haemodialysis
Pregnancy

AOSD: adult-onset Still’s disease; CMV: cytomegalovirus; EBV: Epstein-Barr virus; HHV: human herpesvirus; HIV: human immunodeficiency virus; HSCT: haematopoietic stem cell transplantation; HSV: herpes simplex virus; IBD: inflammatory bowel disease; NK: natural killer; RA: rheumatoid arthritis: sJIA: systemic juvenile inflammatory arthritis; SLE: systemic lupus erythematosus; spp.: species; VZV: varicella zoster virus.

In the UK between 2013 and 2015, 556 women died during pregnancy or up to one year postpartum. Of these, four (0.72%) died as a consequence of HLH. ⁹ Thus, HLH occurring in pregnancy is thankfully rare but is associated with a poor prognosis. It is generally accepted that early treatment of evolving HLH is associated with better outcomes and as such raising awareness of this condition is a crucial start to improve outcomes. ⁵

Pathophysiology

In immunocompetent individuals, natural killer (NK) cells and cytotoxic T-lymphocytes (CTLs) eliminate infected cells by a perforin-dependent pathway. ¹⁰ Cytotoxic cells contain secretory lysosomes that themselves contain perforin and granzymes. When these cells are activated their lysosomes are transported along microtubules toward the synapse between effector and target cell before they can release their contents into the synapse. The perforin and granzymes subsequently mediate apoptotic target cell death resulting in a down-regulation of the immune response. ¹⁰ This process is interrupted in pHLH due to genetic mutations leading to abnormal perforin function and thus an inability to destroy the diseased antigen-presenting cell (APC). Genetic variants, such as low NK cell numbers, may also contribute to individual susceptibility in those who develop sHLH ¹¹ . Furthermore, some pathogens that persist in histiocytes such as Mycobacterium tuberculosis or Leishmania can directly activate toll-like receptors while others, like certain viruses, have developed complex immune evasion strategies that can interfere with NK and CTL cytotoxicity. ¹⁰ Failure to clear such potential antigen triggers from infected, tumour or autoimmune cells leads to uncontrolled activation and proliferation of T-lymphocytes, macrophages and pro-inflammatory cytokines, particularly interferon-gamma (IFN-γ), tumour necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), IL-12, IL-18. This leads to a combination of hyperinflammation, end-organ damage and haemophagocytosis resulting in the clinical manifestations of HLH. The pathophysiology of sHLH will depend on the aetiology but shares the final common pathway of hyperinflammation and organ dysfunction (Figure 1).

Figure 1.

Pathophysiology of sHLH. CTL: cytotoxic T-lymphocyte; IFN-γ: interferon gamma; IL: interleukin; NK: natural killer; sHLH: secondary haemophagocytic lymphohistiocytosis; TNF-α: tumour necrosis factor alpha.

HLH in pregnancy

Primary HLH typically presents in childhood and the diagnosis is often established prior to any pregnancies; however, there is increasing awareness that late onset disease can occur, and genetic testing is, therefore, considered in all cases of HLH in pregnancy. During pregnancy, maternal immune regulation is under additional stress. The role of the placenta is key to acting as an immunological barrier between mother and the semi-allogeneic fetus. ¹² There is evidence that a degree of inflammatory stimulus exists in all pregnancies stemming from the apoptotic debris shed from the syncytial surface of the placenta. ¹³ In specific contexts, the mechanisms that keep this stimulus in check can fail leading to immune dysregulation and hyperinflammation as is observed in pregnancy pathologies such as pre-eclampsia. This context provides a favourable environment for potential secondary HLH triggers such as infection or pre-existing autoimmune diseases such as systemic lupus erythematosus. ¹⁴

Clinical presentation

sHLH is characterised by persistent fever, organ dysfunction, lymphadenopathy and hepato- and/or splenomegaly. Fever is almost universally described, but otherwise the presenting clinical signs and symptoms in adult women with HLH are less typical than in children.^5,15 Importantly, sHLH can arise in a subacute manner, with a gradual amalgamation of features rather than the florid acute presentation more frequently recognised at the point of multiorgan failure. ⁵

To date, 36 cases of sHLH in pregnancy have been reported (Table 2). Clinical descriptors are available for 31 cases showing mostly non-specific presentations that could have been due to sepsis alone and other symptoms and signs that could be due to physiological changes in pregnancy or pregnancy-specific complications. In 26 cases (72% of the tabulated reports), enlargement of the liver, spleen or both is described. Splenomegaly is rarely observed in sepsis alone and should alert the clinician to an alternative underlying disease process such as lymphoma or EBV infection, but this is problematic in pregnancy as mild splenomegaly is a normal finding; ⁴ 48% reported either jaundice or liver function test derangement, the latter common in pregnancy. Furthermore, sHLH has been known to lead to other sequelae of liver pathology, namely encephalopathy and ascites. ⁵⁰ It is also important to note the prevalence of central nervous system (CNS) involvement. Although poorly documented in this cohort, neurological symptoms are an established phenomenon within HLH with a wide spectrum of severity witnessed at presentation. ⁵ This can range from mild cognitive impairment and delirium to more severe CNS manifestations such as seizures, meningoencephalitis, ataxia, hemiplegia and cranial nerve palsies. ⁵¹ CNS involvement is an independent prognostic marker in paediatric HLH. ⁵²

Table 2.

Reported cases of sHLH in pregnancy.

Reported cases of pregnancy-associated sHLH
Case number	Authors	Age (years)	Obstetric history	Gestational age (weeks)	Aetiology	Clinical presentation and laboratory findings	Treatment (except antibiotics)	Maternal outcome	Mode of delivery and fetal outcome
1	Gill et al. 16	30	–	18	–	Fever, hepatomegaly, pancytopenia	IVIg	Remission	40/40 VD – survived
2	Tsuda et al. 17	–	–	–	Parvovirus B19	–	–	–	–
3	Yamanaka et al. 18	–	–	36	–	–	Steroids, IVIg, AT III	Remission	Survived
4	Ishida et al. 19	31	–	–	Hyperemesis	–	Steroids, IVIg	Death	22/40 – IU death
5	Mihara et al. 20	32	–	16	EBV	Fever, pancytopenia, elevated ferritin, LDH, sIL-2R	Steroids, aciclovir  IVIg, gabexate mesilate	Failure Remission	35/40 VD – survived
6	Nakabayashi et al. 21	30	–	21	Pre-eclampsia	Fever, pancytopenia, elevated ferritin, LDH, LFTs	IVIg AT III	Failure Remission	29/40 CS – survived
7	Chmait et al. 22	24	G2 P1	29	EBV	Fever, pancytopenia, elevated LFTs	IVIg, aciclovir, CS	Death	30/40 CS – survived
8	Yamaguchi et al. 23	–	–	–	HSV-2	Fever, pancytopenia, elevated ferritin, TG, sIL-2R	Steroids CsA	Failure Remission	40/40 VD – survived
9	Hanaoka et al. 24	33	G1 P0	21	B-cell lymphoma	Fever, hepatosplenomegaly, pancytopenia, elevated ferritin, TG, LDH, sIL-2R	R-CHOP, HSCT	Remission	28/40 CS – survived
10	Perard et al. 25	28	G4	22	SLE	Fever, pancytopenia, elevated ferritin, TG	Steroids IVIg	Failure Remission	30/40 VD – survived
11	Gonzalez et al. 26	27	–	22	Parvovirus B19	–	Steroids, AT III	Remission	36/40 – survived
12	Chien et al. 27	28	G1 P0	23	–	Fever, bicytopenia, elevated TG	CS delivery	Remission	28/40 CS – survived
13	Teng et al. 28	28	G1 P0	23	AIHA	Fever, bicytopenia, elevated ferritin, TG, LDH, sIL-2R	Steroids TOP	Failure Remission	29/40 CS – death
14	Yoshida et al 29	33	–	PP	SLE	–	Steroids	Remission	Survived
15	Arewa and Ajadi 30	31	G1 P0	21	HIV and malaria	Fever, bicytopenia, jaundice	Antimalarials, HAART, VD	Remission	40/40 VD – survived
16	Dunn et al. 31	41	–	19	AOSD	Fever, rash, headache, anaemia, elevated ferritin, TG, LDH, LFTs	Steroids, CS	Remission	30/40 CS – survived (twins)
17	Hannebicque-Montaigne et al. 32	21	–	29	SLE	Fever, pancytopenia, elevated ferritin, TG	Steroids, IVIg	Remission	38/40 VD – survived
18	Kim et al. 33	29	–	12	SLE	Fever, pancytopenia, elevated ferritin, TG, LDH	CsA, Splenectomy	Remission	14/40 TOP – death
19	Komaru et al. 34	36	G1 P0	40 + 38d	Sjogren’s	Splenomegaly, bicytopenia, jaundice, elevated ferritin, bilirubin, LDH, sIL-2R	Steroids	Remission	40/40 VD – survived
20	Shukla et al. 35	23	G1 P0	10	–	Fever, hepatosplenomegaly, pancytopenia, elevated ferritin, TG, bilirubin	Steroids EPL	Failure Remission	10/40 EPL – death
21	Goulding et al. 36	27	G1 P0	23	HSV-2	Fever, pancytopenia, elevated ferritin	Steroids, aciclovir, Valaciclovir	Remission	24/40 CS – death
22	Klein et al. 37	39	–	30	EBV	Pancytopaenia, elevated ferritin, sIL-2R	Steroids, CsA, etoposide, RTX	Death	31/40 CS – death (twins)
23	Mayama et al. 38	28	G2 P2	19	Parvovirus B19	Fever, pancytopenia, elevated ferritin, LDH	Steroids	Remission	37/40 VD – survived
24	Samra et al. 39	36	–	16	–	Fever, pancytopenia, elevated ferritin, TG	Steroids	Remission	40/40 VD – survived
25	Tumian and Wong. 40	35	G2 P1	38	CMV	Fever, anaemia, jaundice, elevated ferritin, TG, LDH, LFTs, sIL-2R	CS delivery, steroids, CsA	Death	38/40 CS
26	Giard et al. 41	35	G2 P1	13	–	Fever, pancytopenia, jaundice, elevated ferritin, TG, LFTs, sCD25	Steroids, etoposide	Death	22/40 TOP – death
27	Ota et al. 42	26	G1 P0	23	Liver abscess	Fever, thrombocytopaenia, elevated ferritin, TG, LDH, LFTs, sIL-2R	Nil	Death	23/40 – IU death
28	He et al. 43	27	G2 P0	30	NK/T-cell lymphoma	Fever, splenomegaly, pancytopenia, elevated ferritin, LDH, LFTs	Steroids, etoposide, RTX, CS delivery, splenectomy	Death	30/40 CS – survived
29	Ikeda et al. 44	32	–	11	EBV	Fever, bicytopenia, elevated ferritin	Steroids, etoposide, CsA	Remission	11/40 EPL – death
30	Kerley et al. 45	33	G1 P0	22	–	Fever, bicytopenia, elevated ferritin, LDH, LFTs	Steroids Delivery, etoposide, BMT	Failure Remission	22/40 VD – death
31	Rousselin et al. 46	44	G1 P0	30	–	Fever, hepatomegaly, pancytopenia, elevated ferritin, TG, LDH, LFTs	Steroids	Remission	38/40 VD – survived
32	Nasser et al. 47	36	G7 P2	31	HSV-2	Fever, splenomegaly, thrombocytopaenia, elevated ferritin, LDH, LFTs	Steroids, aciclovir, Delivery	Remission	CS – death
33	Cheng et al. 48	–	–	26	–	Fever, bicytopenia, elevated ferritin, TG	Steroids, etoposide	Remission	27/40 TOP – death
34	Parrott et al. 14	28	G2 P1	18	SLE	Fever, splenomegaly, pancytopenia, elevated ferritin, LFTs, sIL-2R, stroke	Steroids, etoposide, IVIg, CsA	Failure	21/40 VD – IU death
35	Parrott et al. 14	37	G4 P3	24	CMV	Fever, thrombocytopaenia, jaundice, elevated ferritin, TG, LFTs, bilirubin, LDH, sIL-2R	Steroids, etoposide	Remission	37/40 VD – survived
36	Yip et al. 49	23	G2 P1	22	–	Fever, pancytopenia, elevated ferritin, TG	Steroids, IVIg Anakinra	Failure Remission	31/40 CS – survived

AOSD: adult-onset Still’s disease; AT III: antithrombin III; BMT: bone marrow transplantation; CMV: cytomegalovirus; CS: caesarean section; CsA: ciclosporin A; d: days; EBV: Epstein-Barr virus; EPL: early pregnancy loss; G: gravida; HAART: highly active anti-retroviral therapy; HIV: human immunodeficiency virus; HSCT: haematopoietic stem cell transplantation; HSV: herpes simplex virus; Ig: immunoglobulin; IU: intrauterine; IVIg: intravenous immunoglobulin; LFTs: liver function tests; LDH: lactate dehydrogenase; NK: natural killer; P: para; PP: postpartum; R-CHOP: rituximab: cyclophosphamide: doxorubicin: vincristine: prednisolone; RTX: rituximab; sCD25: soluble CD25; sIL-2R: soluble interleukin-2 receptor; SLE: systemic lupus erythematosus; TOP: termination of pregnancy; TG: triglycerides; VD: vaginal delivery.

Pulmonary manifestations of sHLH are common but may contribute to the diagnostic delay given the risk of attributing these symptoms to other, more common, diagnoses. A national retrospective cohort study identified lung involvement in 54% of cases with dyspnoea and cough occurring most frequently. ⁵³ These symptoms were not frequently represented in published cases of sHLH in pregnancy (Table 2). However, the authors recommend high clinical suspicion for those with these symptoms and supportive radiological changes such as interstitial infiltrates with centrilobular nodules, ill-defined consolidation and localised ground-glass opacities on chest imaging. ⁵³

A wide spectrum of rashes has been reported in HLH ranging from non-specific erythematous macules to petechiae or purpura. In large non-pregnant cohorts, 25% of adults with HLH have cutaneous involvement. ⁵ Only one case of pregnancy-associated sHLH reported a diffuse erythematous macular rash at presentation. ³¹ Nodular lesions should raise suspicion of associated T-cell lymphoma. ⁵

Diagnosis

The diagnosis of HLH can be difficult and a number of diagnostic criteria exist. The most widely used diagnostic criteria, HLH-2004, were established for paediatric women under 18 years of age (Table 3). ⁵⁴ To date, there are no validated criteria for diagnosis of HLH in adults, although there is a composite probability score for sHLH, the HScore, which is commonly used but has not been validated in pregnancy. ² The HScore uses clinical parameters, common laboratory values and bone marrow findings dependent on their HLH specificity and calculates a probability score (Table 4). ⁵⁵ The higher the HScore out of a total of 337, the higher the likelihood of HLH. It should be further highlighted, however, that there is currently no well-validated means of diagnosing HLH in adult women, and that all available paradigms (including HScore) are limited by their lack of specificity for HLH. Many critically ill women will score highly using these paradigms whether they have HLH or not. ⁵⁶

Table 3.

HLH-2004 diagnostic criteria (for use in non-pregnant individuals). ⁵⁴

HLH-2004 diagnostic criteria (≥5 of 8 criteria below)
1. Fever
2. Splenomegaly
3. Cytopenia affecting ≥2 of 3 peripheral blood lineages – Haemoglobin < 90 g/L – Platelets < 100 ×109/L – Neutrophils <1.0 × 109/L
4. Hypertriglyceridaemia and/or hypofibrinogenaemia – Fasting triglycerides ≥3.0 mmol/L – Fibrinogen ≤1.5 g/L
5. Haemophagocytosis in bone marrow, spleen or lymph nodes with no evidence of malignancy
6. Low or no NK cell activity
7. Ferritin ≥500 µg/L
8. Soluble CD25 (i.e. soluble interleukin-2 receptor, sIL-2R) ≥2400 U/ml

Table 4.

HScore parameters and points. ⁵⁵

Parameter	Number of points
Known underlying immunosuppression	No 0 Yes +18
Temperature (°C)	<38.4 0 38.4–39.4 +33 >39.4 +49
Organomegaly	No 0 Hepatomegaly or splenomegaly +23 Hepatomegaly and splenomegaly +38
Cytopenia lineage(s)	1 0 2 +24 3 +34
Ferritin (µg/L)	<2000 0 2000–6000 +35 >6000 +50
Triglyceride (mmol/L)	<1.5 0 1.5 − 4 +44 >4 +64
Fibrinogen (g/L)	>2.5 0 ≤2.5 +30
Aspartate aminotransferase (U/L)	<30 0 ≥30 +19
Haemophagocytosis on bone marrow aspirate	No 0 Yes +35

Importantly, not all markers used in these scoring systems will be routinely checked and they may be initially normal. Trends of biochemical values over time can also be revealing. We suggest the measurement of serum ferritin in any individual who is unwell and has a fever. Subsequently, the other markers of HLH, such as serum lipids and more specific tests such as the soluble interleukin-2 receptor can be requested (Figure 2). Ferritin is a glycoprotein that stores iron which it releases in a controlled manner in the absence of inflammation. ⁵⁷ It is also an acute phase reactant, and as such is non-specifically elevated in a wide range of inflammatory states, including acute infection, malignancy, chronic kidney disease and a variety of autoimmune conditions. ⁵⁸ During pregnancy, the serum ferritin initially rises in women with adequate iron stores at conception reaching a peak of approximately 230 µg/L during the second trimester.^57,59 This is followed by a progressive fall by 32 weeks due to haemodilution and mobilisation of iron to approximately half of the pre-pregnancy levels, before a further mild elevation in the third trimester.^57,60 Marked hyperferritinaemia (>10,000 µg/L) is 96% specific and 90% sensitive for HLH in the paediatric population. ⁶¹ It is less specific for HLH in adults, but significantly elevated levels should still raise suspicion. ⁶² However, in some adults, even with severe life-threatening HLH, milder elevations are observed. ² Values between 7000 and 10,000 µg/L are often reported in this context, while a separate analysis of 50 adult women with HLH revealed a median ferritin level on presentation of 5823 µg/L. ⁶²

Figure 2.

Proposed algorithm for investigation of suspected HLH in pregnancy. AFB: acid-fast bacillus; ALT: alanine aminotransferase; ANA: antinuclear antibody; ANCA: anti-neutrophil cytoplasmic antibody; AST: aspartate aminotransferase; C: complement; CMV: cytomegalovirus; COAG: coagulation studies; CRP: c-reactive protein; CT: computerised tomography; dsDNA: double-stranded DNA; EBV: Epstein-Barr virus: ENA: extractable nuclear antigen; ESR: erythrocyte sedimentation rate; FBC: full blood count; HAV IgM: hepatitis A immunoglobulin M; HBcAb: hepatitis B core antibody; HBsAg: hepatitis B surface antigen; HCV: hepatitis C virus; HEV: hepatitis E virus; HHV: human herpesvirus; HIV: human immunodeficiency virus; HSV: herpes simplex virus; Igs: immunoglobulins; LDH: lactate dehydrogenase; LFTs: liver function tests; MC&S: microscopy culture and sensitivity; MRI: magnetic resonance imaging; NK: natural killer; PCR: polymerase chain reaction; RF: rheumatoid factor; sCD25: soluble CD25; sIL-2R: soluble interleukin-2 receptor; TG: triglyceride; US: ultrasound.

Soluble CD25 (sCD25), the soluble interleukin-2 receptor (sIL-2R) is a useful diagnostic marker for HLH especially in paediatric populations but is not yet readily available in all laboratories and its use in pregnancy has not been validated. sCD25 is a heterotrimeric transmembrane protein that is upregulated on activated T-cells, thus high levels are found in HLH, lymphoma and other conditions where T-cell activation is prevalent. ⁶³ The test itself is based on a low-cost commercially available assay. A recent study has shown that the specificity of sCD25 in adults fails to match that seen in the paediatric population. ⁶⁴ Thus, further work is required in adult cohorts with and without HLH to determine more accurate sensitivity and specificity values for this assay. It is also notable that the extent of elevation of sCD25 above 10,000 U/ml has not been shown to be of prognostic significance. ⁶³

Pregnancy will alter the interpretation of some of the biochemical markers typically used in the diagnosis of HLH. In the HScore, it is the ferritin and triglycerides that confer the most diagnostic weight. A pregnant woman with persistent fever and cytopaenia affecting at least 2 peripheral blood lineages presents a particular diagnostic challenge because, as well as infection, a number of pregnancy-specific conditions may present similarly. These include acute fatty liver of pregnancy and haemolysis, elevated liver enzymes and low platelet count (HELLP) syndrome. Indeed, sHLH and HELLP syndrome may coexist, thus a high degree of suspicion is warranted. ⁴⁵ Lipids including cholesterol and triglycerides tend to increase in pregnancy and are infrequently measured. The normal ranges have not been established and so while it is appropriate to measure triglycerides if HLH is suspected in pregnancy, the results should be interpreted with caution.

In all cohorts of sHLH, including those occurring in pregnancy, many cases are initially treated for sepsis. Indeed, there is a known subset of septic women whose infection will cause an aberrant cytokine cascade due to immune dysregulation, resulting in the clinical syndrome of sHLH. Furthermore, sHLH can further predispose to sepsis, creating a diagnostic and therapeutic challenge. The presentation of the two syndromes may be identical, with multi-organ failure and disseminated intravascular coagulopathy (DIC) occurring in severe phenotypes, making it necessary to consider sHLH in any individual with sepsis not responding to conventional antimicrobials. Very elevated ferritin levels and progressive cytopenia (particularly reduction in platelet count) can be signs of evolving HLH and are useful markers in this context. ⁵⁴

Initial investigations should be tailored to the diagnostic criteria listed in Table 3 and include full blood count, blood film, coagulation screen (including fibrinogen) and erythrocyte sedimentation rate (ESR). ESR is affected by pregnancy but, like many investigations in HLH, single measurements are unhelpful but trends of measurements over days can be enlightening. A high ESR due to infection or pregnancy will fall due to fibrinogen consumption as HLH evolves. ⁶⁵ Anaemia is common in pregnancy due to fetal demand for iron and haemodilution. ⁵⁷ However, the downward haemoglobin trend is much more marked in evolving sHLH in pregnancy, and the blood film often reveals concomitant thrombocytopenia. Microcytic hypochromic red cells and characteristic pencil cells of iron deficiency may also be observed, but these are not accompanied by low ferritin levels in sHLH. Fibrinogen is classically low due to consumption in HLH and raised in infection. Thus, daily haematology tests are required to create trends to guide the suspecting clinician.

Biochemistry to assess for end-organ damage (renal profile and hepatic function), ferritin, lipids (including triglycerides), lactate dehydrogenase (LDH), C-reactive protein (CRP) and haematinics should also be performed and repeated regularly. sCD25 should be sent in all cases, but the results typically take many weeks and do not currently assist in the immediate diagnostic phase unless in a specialist centre. Genetic testing for pHLH genotypes should be considered in all young adults, women with a family history, those with EBV-driven sHLH and also requested in those in whom no cause for their HLH can be identified.

Further investigations should be geared towards elucidating the underlying aetiology. Bacterial blood cultures should be taken alongside serum for EBV and CMV serology and PCR, viral hepatitis screen for Hepatitis A, B and C, human immunodeficiency viruses (HIV) and Parvovirus B19. Given the higher prevalence of autoimmunity in women of childbearing age, we advocate the testing of antinuclear antibodies (ANA), extractable nuclear antigens (ENA), antineutrophil cytoplasmic antibodies (ANCA), complement (C3 and C4) and double-stranded DNA (dsDNA) levels in all cases.

Bone marrow examination should be performed in all cases, where possible, as it will not only confirm the presence of haemophagocytic activity but aid in the diagnosis of underlying haematological malignancies as the driver for the disease. The presence of haemophagocytosis in the bone marrow is not, however, diagnostic for HLH; it can be seen in other settings such as after blood transfusion and chemotherapy, in fulminant sepsis, and after surgery. ⁶⁶ The absence of haemophagocytosis on the marrow examination does also not exclude the diagnosis, if clinical suspicion and other markers are supportive. ⁵ A few small studies have investigated the quantification of haemophagocytosis in the marrow and its correlation with the eventual diagnosis of HLH. A case-control study, using aspirates only, showed the extent of haemophagocytosis to be higher in those with HLH with a sensitivity of 83% and a specificity of 60%. ⁶⁷ A larger blinded retrospective study evaluating 64 bone marrow aspirates and core biopsy specimens from adult women with a clinical phenotype suspicious for sHLH revealed no correlation between the amount of haemophagocytosis observed and clinical disease. ⁶⁶

Often imaging may be required in the diagnostic work-up. Magnetic resonance imaging (MRI) of the brain and culture of cerebrospinal fluid may be appropriate in the context of neurological involvement, while cross-sectional imaging using computerised and/or positron-emission tomography followed by targeted lymph node or solid organ biopsy can identify malignancy. The use of imaging techniques involving ionising radiation may be appropriate in pregnancy but should be discussed in a multidisciplinary team (MDT), and alternatives considered.

A suspected diagnosis of sHLH in pregnancy should be urgently discussed with a regional expert or in a specialist multidisciplinary team (MDT) HLH meeting, as the complexities of treatment may require the need for early specialist transfer if it safe to do so given the associated high mortality.

Treatment

The treatment of sHLH typically involves management of the underlying cause, which may not be easily identified. In the interim, empirical immunosuppressive treatment based is generally advocated in order to rapidly suppress the hyperinflammation and buy time to identify the underlying trigger, allowing for more targeted definitive treatment of the underlying aetiological driver. Delivery must be considered in each case of HLH in pregnancy and has been shown to lead to rapid clinical and biochemical resolution in some cases. ²⁸

Typically, glucocorticoids and intravenous immunoglobulin are used to rapidly suppress the acute phase response and to allow time for diagnostic investigations to both confirm the clinical suspicion of HLH and look for the underlying aetiology. The widely used paediatric HLH-94 protocol includes the use of high-dose dexamethasone, the topoisomerase II inhibiting alkylating agent etoposide, the calcineurin inhibitor ciclosporin A (CsA) and employs intrathecal methotrexate in cases with central nervous system involvement. ⁶⁸ However, this is not necessary in many cases of sHLH where immunosuppression and treatment of the underlying driver of the HLH can lead to resolution. In the last decade, the use of targeted cytokine inhibition has been introduced to the management of HLH, and can lead to a rapid clinical response. ⁶⁹

Non-selective immunosuppressive agents

Glucocorticoids

Glucocorticoids mediate anti-inflammatory effects on both genomic and non-genomic levels when bound to the intracellular glucocorticoid receptor (GR). Classically, high-dose glucocorticoids such as intravenous methylprednisolone or dexamethasone are used; the latter has greater anti-macrophage activity and is the glucocorticoid of choice in this condition. Furthermore, dexamethasone has particular use in the context of neurological involvement as it has the capacity to permeate across the blood–brain barrier, but dose-related caution should be implemented to avoid CNS toxicity. ⁷⁰ Methylprednisolone is often preferred in pregnancy due to reduced placental transfer compared to dexamethasone, and is therefore the glucocorticoid if no clear CNS involvement.

In cases where the underlying sHLH trigger has been elusive, high-dose steroid use can blur the diagnostic picture. As aforementioned, a common driver of sHLH is lymphoproliferative disease, which can be exquisitely sensitive to glucocorticoids. Therefore, their early use in sHLH cases may obviate the swift diagnosis of lymphoma resulting in additional investigations and the need for repeat sampling once disease-masking doses have been weaned.

Intravenous immunoglobulin

The use of intravenous immunoglobulin (IVIg) is safe and in combination with glucocorticoids forms the backbone of some HLH treatment regimens. Like many interventions in sHLH, however, evidence is lacking.^71,72 It achieves its anti-inflammatory effects by competitively binding to the Fc-receptor on macrophages, causing downstream modulation of B- and T-cell activity, and inhibiting complement activation. ⁷³ Clinical experience over many years of its use for the treatment of autoimmune conditions in pregnancy does not suggest any harmful effect to the developing fetus, nor the infant during breastfeeding. ⁷⁴ IVIg is expensive, however, and supplies can be restricted.

Corticosteroids and IVIg are both used in the management of pregnancy-associated sHLH, but their combined use is not always enough to induce remission.^14,75

Selective immunosuppressive agents

Calcineurin inhibitors

Ciclosporin A (CsA) is a calcineurin inhibitor that binds to the receptor cyclophilin-1 leading to downstream effects that inhibit the transcription of key inflammatory cytokines, such as IL-2. This leads to the downregulation of activated T-cells. ⁷⁶ CsA has been used in severe cases of pregnancy-associated sHLH refractory to corticosteroids with varying results.^23,40 It has been seen to be most effective in sHLH secondary to autoimmune disease. ² Often in these cases there is a suboptimal response to corticosteroids alone, and CsA is used as a potent adjunct to first-line therapy. Its early introduction in those treated with HLH-94 etoposide-dexamethasone based regimens did not improve outcomes, however. ⁷¹

CsA has a favourable safety profile in pregnancy derived from long-term solid organ transplant data. ⁷⁷ Prematurity and intrauterine growth restriction (IUGR) leading to low infant birthweights have been reported but CsA does not appear to be a human teratogen. ⁷⁷ Long-term data are still required to consolidate its safety during breastfeeding, but there are no reports of adverse effects on growth, development or renal function despite varying recorded levels of CsA in breast milk. ⁷⁸

Cytokine inhibitors

Anakinra

Anakinra, a recombinant IL-1 receptor antagonist (IL-1Ra), has become favoured in recent years due to its excellent safety profile, rapid onset of action and its short half-life. ⁷⁹ It provides a physiological steroid-sparing path to IL-1 downregulation resulting in additional time for further investigation of the underlying aetiology. ⁸⁰ Anakinra requires daily dosing and can be administered either via subcutaneous or intravenous routes. Fewer than 50 cases of anakinra use in pregnancy have been reported.^81–84 The majority completed successful pregnancies to term with normal neonatal checks. One case of fetal unilateral hearing loss and two cases of renal agenesis have been reported. A causal link between anakinra and renal agenesis is uncertain as in both cases there was maternal illness (uncontrolled inflammation in one case and the other a twin pregnancy in a woman with autoimmune disease and glucocorticoid-induced diabetes mellitus). ⁸⁵ Anakinra is considered appropriate to use in pregnancy, and no concerns have been identified with its ongoing use in breastfeeding in a large international multicentre study. ⁸⁶

Tocilizumab

Tocilizumab (TCZ) is a monoclonal antibody that targets the receptor of IL-6. It is widely used in systemic-onset juvenile arthritis and adult-onset Still’s disease which can lead to sHLH. ⁶⁹ By inhibiting IL-6, TCZ effectively abrogates the acute phase response leading to normalisation of measurable parameters of inflammation and infection such as fever, CRP and ferritin but is not necessarily synonymous with disease control. ⁸⁷

There are currently no controlled studies of TCZ use in human pregnancy; the current literature of 360 exposed pregnancies demonstrates cases of congenital anomaly, miscarriage, preterm delivery and low birth weight, seen at a similar incidence when compared to rates in the unexposed pregnant population. ⁸⁸

Etoposide

Etoposide is a chemotherapeutic drug primarily used in cancer treatment. It selectively inhibits topoisomerase II preventing re-ligation of DNA strands leading to acquired errors in DNA synthesis and apoptosis of cancer cells. Etoposide selectively induces apoptosis of activated T-cells leading to a marked reduction in inflammatory cytokine production while sparing memory T-cells. ⁸⁹ The HLH-94 paediatric treatment protocol contains etoposide as a key component, and its adapted use in adults, extrapolated from this, is often effective at reversing the life-threatening sequelae of sHLH. ⁷¹ Dose reduction is advised if renal impairment is present, as etoposide is primarily renally excreted. ⁹⁰ Etoposide’s potential toxicity to the fetus is an obvious concern in the treatment of sHLH in pregnancy. Although there is no statistically significant increase in the number of congenital malformations seen in pregnancies exposed to chemotherapy after the first trimester, ⁹¹ etoposide use after this time has been seen to result in adverse fetal ovarian development in mice studies. ⁹² However, the clinical scenario may warrant the use of the drug in pregnant women despite potential risks although delivery would have to be strongly considered. ⁹³

Emapalumab

Emapalumab is a fully human immunoglobulin G1 monoclonal antibody directed against IFN-γ developed for use in HLH. Favourable outcomes have been observed in paediatric cases of refractory pHLH. ⁹⁴ A phase 2/3 interventional study (NCT03985423) is currently recruiting adult women to assess the efficacy, safety and pharmacokinetics of emapalumab in sHLH, but severe infections have been noted in the existing data. ⁹⁵ No data exist relating to the use of emapalumab in the context of pregnancy and breastfeeding in humans. ⁹⁶

Ruxolitinib

Ruxolitinib is a selective inhibitor of the Janus-associated tyrosine kinases JAK1 and JAK2, whose role in the JAK/STAT signalling pathway contributes to the cytokine-mediated hyperinflammatory state seen in sHLH. ⁹⁷ It is used in the treatment of myeloproliferative neoplasms such as myelofibrosis and polycythaemia vera, but promising results in the context of adult HLH have been observed in pre-clinical trials and case series.^97,98 A phase 2 interventional study (NCT02400463) is currently recruiting adult women to assess efficacy and safety of ruxolitinib in sHLH and the preliminary data are encouraging in both regards. ⁹⁹ There are no current data for its use in the context of pregnancy. Tofacitinib, another JAK inhibitor used in the treatment of rheumatoid arthritis, psoriatic arthritis, and ulcerative colitis, has been shown to be teratogenic in rats, thus its use in pregnancy is currently largely contraindicated despite a human study revealing adverse rates comparable to the unexposed background risk.^100,101

B-cell depletion

Rituximab

There are known triggers for sHLH in pregnancy where the use of rituximab, a genetically engineered chimeric murine/human monoclonal antibody that targets CD20, may be indicated. Typically, it is used in conjunction with glucocorticoids and IVIg (and cytokine inhibitors) in the treatment of sHLH due to B-cell lymphoma, severe systemic lupus erythematosus and in EBV-driven HLH where rituximab is used repeatedly to deplete the B-cells in which the virus is actively replicating. ³⁷

Rituximab use in pregnancy can lead to B-cell depletion in the fetus if given beyond 16 weeks of gestation, increasing the potential risks of neonatal infection. ¹⁰² Congenital abnormalities have also been reported; however, its use is generally considered acceptable if indicated in a pregnant woman with sHLH, and other conditions where there are no suitable alternative options. ¹⁰³

Transplantation

Haematopoietic stem cell transplantation (HSCT) is established for pHLH and refractory sHLH including those occurring in pregnancy but only performed postpartum. Successful outcomes have been reported after delivery and focused chemotherapy. ²⁴ Despite the commonly reported occurrence of HSCT-related infertility, women are able to retain or recover fertility and conceive. ¹⁰⁴

Delivery

Maternal and fetal outcomes following delivery in reported cases of HLH in pregnancy are mixed (Table 2). Emergency caesarean sections were performed in cases where fetal complications were observed, but they were more frequently undertaken to aid maternal treatment and complete remission was occasionally achieved after delivery.^28,45,47 This raises a key question – does early delivery lead to better outcomes? This has yet to be proven and so delivery is not mandated when the diagnosis is made, but close monitoring of mother and fetus is required, and delivery performed if the mother’s condition is deteriorating, or if there is evidence of fetal compromise. ⁹

Future pregnancies

Future pregnancies for any woman following HLH in pregnancy should be carefully considered and planned. If there was a clear and transient trigger for the sHLH in pregnancy, such as infection, there is no suggestion that subsequent pregnancies will lead to recurrence; however, caution is advised. A caveat to this is if the infection is triggered by EBV, genetic testing for underlying primary HLH is strongly advised. For those with autoimmune disease such as SLE, which may have presented as sHLH in pregnancy, future pregnancies should be carefully planned, taking place following adequate disease control and on non-teratogenic treatment regimens. If the cause for sHLH in pregnancy was not identified, we suggest genetic testing and referral to a specialist HLH centre for investigation prior to the planning of subsequent pregnancies.

Conclusion

HLH in pregnancy is a rare, but likely underdiagnosed, subtype of a complex life-threatening multisystem inflammatory syndrome. It provides significant diagnostic challenges due to its spectrum of underlying aetiologies and the subsequent diagnostic delay contributes to the high mortality seen. Serum ferritin measurement can hint at the diagnosis of sHLH in pregnancy and trigger further investigation and involvement of specialists early in the disease course. The use of immunosuppression and more targeted therapies presents more efficacious and less toxic treatment options. The interleukin-1 receptor antagonist, anakinra, is particularly attractive in this setting due to its established efficacy and physiological nature, but more importantly its short half-life lends itself well to use in hyperinflammation triggered by infection. Refractory cases may require difficult decisions to be made regarding delivery and the use of more toxic treatment regimens. Future pregnancies need to be carefully considered in the context of the underlying aetiology of the HLH. Particularly, caution should be taken in those in whom an aetiological trigger has not been identified.

Ethical approval/ informed consent

Obtaining patient consent or ethical approval is not applicable for this manuscript.