Hemophagocytic Syndrome in an Adolescent With Crohn Disease Receiving Azathioprine and Infliximab

Abstract

Hemophagocytic lymphohistiocytosis (HLH) is a rare but potentially fatal disorder. It is characterized by excessive proinflammatory cytokine release and proliferation of activated macrophages and lymphocytes that phagocytose erythrocytes, white blood cells, and platelets in the bone marrow. Clinically, it presents with high persistent fever and splenomegaly, often in the context of an acute infection (1). Laboratory signs include peripheral blood cytopenias (affecting at least 2 cell lines), splenomegaly, hypertriglyceridemia (≥265 mg/dL), hyperferritinemia (≥500 ng/mL), elevated soluble CD25, and/or hypofibrinogenemia (≤150 mg/dL) (1,2). It is broadly classified into 2 forms. Primary HLH is an inherited autosomal recessive disorder associated with mutations of proteins involved in either the functional secretion of cytotoxic granules, or the delivery of proteases required for apoptosis of target cells. Secondary HLH is associated with certain infections, including Epstein-Barr virus (EBV) infection and other diseases (1). Patients with immunodeficiency or immunosuppression are at risk for infection-associated HLH. Therefore, patients with inflammatory bowel disease (IBD) treated with immunomodulators probably represent a susceptible population (3). We report an adolescent with Crohn disease in whom EBV-associated HLH developed while she was receiving maintenance therapy with azathioprine and infliximab. CASE REPORT An 18-year-old girl had presented at 15 years of age with dysphagia, weight loss, secondary amenorrhea, and perianal tags, but no diarrhea. Endoscopy showed esophageal ulcers with chronic inflammation and granuloma on biopsy, gastritis with poorly formed granuloma, and duodenitis with subtotal villous atrophy. The result of a small bowel series was normal. She received a diagnosis of Crohn disease and was given concurrent prednisone and azathioprine, with remission of symptoms. Prednisone was weaned gradually after 4 weeks. However, her dose of azathioprine was increased from 75 mg to 100 mg to 125 mg during 6 months because of symptom recurrence (abdominal pain, diarrhea) and low red blood cell (RBC) 6-thioguanine (6-TG) concentrations. Her 6-TG was 166 pmol/8 × 108 RBC after she had received 125 mg azathioprine for 3 months. On 5 occasions in the year before admission, 6-methyl mercaptopurine levels were determined, and all results were below the hepatotoxic range (5700 pmol/8 × 108 RBC); the level 1 month before admission was 790 pmol/8 × 108 RBC. Owing to her frequent abdominal pain and diarrhea while she was receiving maintenance azathioprine, requiring additional courses of prednisone, she was given 5 mg/kg per dose infliximab approximately 6 months after diagnosis. She required dose escalation to 10 mg/kg per dose 12 months later because of disease flareups. Routine determinations of complete blood count (CBC), amylase, lipase, and hepatic panel checked every 2 to 3 months remained normal while she was receiving combined azathioprine and infliximab. Her last routine follow-up visit was 2 months before admission. She had received a total of 5600 mg infliximab for 2 years when approximately 1 week before her next scheduled infusion, she experienced sore throat, fatigue, fever, headache, rhinorrhea, cough, and crampy abdominal pain. These symptoms persisted for 1 week without improvement. She then experienced anorexia and dark urine, prompting evaluation at a local emergency department. There she was diagnosed with an influenza-like illness, given intravenous fluid hydration, and discharged home. A complete blood count at that time showed mild depression of her blood cell lines (white blood cells 3.2 K/μL [normal 4.5–13.5 K/μL]; hemoglobin 11 g/dL [12–15 g/dL]; platelets 177 K/μL [150–350 K/μL]) and evidence of hepatitis and liver synthetic dysfunction (aspartate aminotransferase 103 IU/L [15–45 IU/L]; alanine aminotransferase 149 IU/L [7–35 IU/L]; albumin 3.3 g/dL [3.8–5.4 g/dL]; prothrombin time 14.3 seconds [11–14 seconds]; partial thromboplastin time 30.4 seconds [27–40 seconds]. A day later her symptoms had not improved, so she was admitted for further evaluation. On physical examination she had an oral temperature of 38°C, a heart rate of 103 beats/minute, and a respiratory rate of 19/minute. She had mild jaundice and a diffuse morbilliform rash on her chest. Her pharynx was erythematous, with tonsillar enlargement and white plaques. She had two 1-cm lymph nodes palpable in the left posterior cervical chain. Her heart and lungs were normal, except for tachycardia. Her abdomen was not tender, and she had no hepatosplenomegaly. Perianal examination showed several skin tags but no abscess or fistula. Her pulses and capillary refill were normal. Her admission CBC was significant for leukopenia (white blood cells 3.1 K/μL) and anemia (hemoglobin 11.6 g/dL). Her platelet count was 184 K/μL, lower than on a CBC 2 months earlier (361 K/μL). A chemistry panel showed total bilirubin of 4.2 mg/dL [0.3–1.2 mg/dL], mostly conjugated, aspartate aminotransferase 189 IU/L, alanine aminotransferase 108 IU/L, γ-glutamyltransferase 236 IU/L [7–32 IU/L], and albumin 3.1 g/dL. The results of blood cultures and of screening for influenza A/B and parvovirus B19 were negative. Cytomegalovirus (CMV) immunoglobulin (Ig) M, urine CMV, and CMV polymerase chain reaction were negative, but IgG was positive, consistent with previous CMV infection. EBV IgM against viral capsid antigen was positive, indicating recent EBV infection. A diagnosis of infectious mononucleosis with secondary hepatitis and bone marrow suppression was made. Azathioprine was stopped when she was admitted, and infliximab was held. She continued to have an elevated temperature, mostly nocturnal (≤39.5°C), poor appetite, and malaise, and mouth ulcers developed. Anemia, leukopenia, and hepatitis persisted. Three days after admission, HLH was suspected. EBV copy number by quantitative polymerase chain reaction was 54 000 copies/mL [normal <200 copies/mL), and ferritin was 2074 ng/mL [10–120 ng/mL], but triglycerides were only mildly elevated at 162 mg/dL [36–126 mg/dL] while she was receiving parenteral nutrition. Her liver and spleen were not palpable, so the classic diagnostic criteria for HLH were not fulfilled. She experienced bloody diarrhea and was given on 5-ASA (Asacol). The stool culture results were negative for Shigella, Salmonella, Campylobacter, and Clostridium difficile toxin. On the seventh hospital day, intravenous acyclovir was started to treat EBV infection because of her continuing elevated temperature. The next day, her ferritin was 3480 ng/mL, triglycerides 219 mg/dL, and EBV copy number was 61 000 copies/mL. The consultant hematologist performed a bone marrow aspiration and biopsy. This showed normocellular marrow with myeloid left shift, megaloblastic erythroid maturation, polyclonal plasmacytosis, absence of iron stores, and several erythrophagocytic elements. The diagnosis of viral-associated HLH was considered. Other markers of HLH were investigated at a reference laboratory (Children's Hospital of Cincinnati), but these results were not available for 2 weeks after presentation. This included natural killer (NK) cell function, which was much decreased, with no NK cells detected in the sample. Plasma soluble IL-2 receptor alpha was markedly increased (20 720 pg/mL [186–2678 pg/mL]). Additionally, normal perforin expression was detected by flow cytometry, and granzyme B expression was increased in cytotoxic cells. These results were consistent with infection-associated HLH. Owing to the lack of symptom improvement, with ongoing elevated temperature, development of pulmonary infiltrates with tachypnea, and oxygen requirement suggesting early adult respiratory distress syndrome, it was decided to commence therapy for presumed EBV-induced HLH with intravenous dexamethasone 7 mg every 12 hours. This was associated with rapid improvement, with resolution of fever after 24 hours, and improvement of respiratory distress. Laboratory evaluation showed steady recovery of peripheral blood counts and liver tests, decreased serum ferritin, triglycerides, and EBV copy number. She was discharged home 4 days later with a regimen of oral dexamethasone. This was subsequently weaned, and she has been well for 29 months with no recurrence of HLH. Treatment for Crohn disease continues with oral prednisone 10 mg on alternate days. Other immunosuppressant medications have not been reinstituted for fear of HLH relapse. Her EBV copy number had declined to 80 copies per 5 lymphocytes 2 months after presentation. DISCUSSION To our knowledge, this is the first report of EBV-associated HLH in a patient with Crohn disease treated with both azathioprine and infliximab. Previous reported cases of infection-associated HLH in patients with IBD include 4 associated with CMV (4–7), 1 with histoplasmosis (8), 1 with EBV (9), and 1 with Mycobacterium tuberculosis(3), treated with prednisone, immunomodulators, and/or infliximab. Two cases were fatal. It is possible that the combined immunosuppressive effects of our patient's treatment regimen impaired her ability to respond normally to a primary EBV infection. Although thiopurine methyl transferase genotype or activity is unknown in this patient, it is unlikely that she has partial or total deficiency, given that her 6-TG concentration was low while she was receiving a stable dosage of azathioprine of 2.2 mg · kg−1 · day−1, her 6-MMP levels were under the hepatotoxic range, and leukopenia never developed before the development of HLH. However, her dosage of infliximab was 10 mg/kg, on the high end of the therapeutic range when she had this complication (anti-infliximab antibodies and infliximab levels were not obtained). There was no family history or history of consanguinity, or specific mutations in the perforin gene to suggest an inherited hemophagocytic syndrome. This case illustrates the difficulties in making the diagnosis of HLH. The clinical symptoms of HLH are the result of an exaggerated inflammatory response and may mimic those of a viral infection (10,11). In our patient it was difficult initially to distinguish the symptoms of primary EBV infection from those of HLH. Therefore, a high degree of clinical suspicion was critical to ensure early diagnosis and treatment. The diagnosis of HLH can be challenging because major diagnostic criteria may not be fulfilled (12). For example, our patient's bone marrow did not have classic findings, her serum triglycerides were not markedly elevated, and she had no splenomegaly. In addition, the results of confirmatory bone marrow test results (eg, NK cell activity, soluble IL-2 receptor) were not immediately available. However, she had prolonged elevated temperature (>38.5°C); elevated serum ferritin; decreased red blood cell, white blood cell, and platelet counts; and hepatitis. These observations, together with the bone marrow finding of occasional hemophagocytosis and the presence of active EBV replication, supported the diagnosis of secondary HLH. It is important to realize that not all of the diagnostic criteria for HLH need to be fulfilled before the institution of lifesaving therapies, because many patients do not meet the full diagnostic criteria until late in the course of their disease. Such early therapeutic interventions often need to be implemented on the basis of strong clinical suspicion for HLH to prevent irreversible end-organ damage (1). This patient received dexamethasone, with prompt clinical response. However, patients with HLH may need more aggressive chemotherapy (1). Despite reports that milder forms of HLH improve with discontinuation of immunosuppression (4), our patient did not respond to the suspension of azathioprine and infliximab alone. Ultimately, our patient did meet the criteria for secondary HLH when the results of her NK cell function tests became available. HLH is a serious disorder. Inasmuch as it can be induced by common viruses in the immunosuppressed patient, physicians caring for patients with chronic illnesses, such as IBD, who require immunosuppressants should be alert to the possibility of HLH. The challenge moving forward is the treatment of her Crohn disease. Owing to the low-grade persistent EBV, she has received maintenance therapy of alternate-day prednisone with no recurrence of digestive symptoms. In previous cases, remission was maintained with mild anti-inflammatory therapy with mesalamine and low-dose prednisolone. In case of a flare-up, therapy will need to carefully balance necessary immunosuppression and disease control, while monitoring EBV replication.