Neutrophil-Predominant Leukocytosis Induced by Infliximab Infusion for Ulcerative Colitis

Few case reports have documented leukemoid reactions after infliximab infusions.The following report describes a case of marked leukocytosis in a 19 year old male who underwent an infliximab infusion for uncontrolled ulcerative colitis and subsequently developed a leukocytosis of 53,000/microliter with a neutrophilia without any other identified source.A 19 year old male with uncontrolled ulcerative colitis (UC) and recurrent Clostridium difficile colitis presented to our hospital with complaints of up to 32 bowel movements a day and abdominal pain.On presentation, vital signs were stable and his physical exam was notable for diffuse tenderness to palpation in the umbilical area without guarding or rebound.Laboratory studies were significant for a leukocytosis of 18,100/microliter with 69% neutrophils and thrombocytosis of 687,000/microliter; c-reactive protein was elevated at 4.74 mg/dl, basic metabolic panel was unremarkable and C.difficile toxin was negative. He was started on intravenous steroids.He had computerized tomography of the abdomen and pelvis with contrast and flexible sigmoidoscopy with biopsies showing moderate-severe inflammation from the rectum to the descending colon confirming severe ulcerative colitis.Patient had his third infliximab infusion 3 days after admission.He tolerated the infusion well with symptomatic improvement however, his laboratory studies were notable for a leukocytosis of 53,000/microliter with 70%neutrophils and 20% bands.Infectious workup was unremarkable, and the white blood cell count decreased to 20,000/microliter on discharge.On follow-up, his serum infliximab concentration was undetectable (< 1.0 micrograms/ml) and infliximab antibody levels were positive at 24.4 U/ml (normal < 3.1 U/ml), and his medication was changed to vedolizumab. Only two other case reports describe leukemoid reactions with an associated neutrophilia in the setting of infliximab infusions.One described a delayed type infusion reaction - most likely a systemic lupus-like syndrome, while the second one described a case of acute respiratory distress syndrome post-infusion.As these cases demonstrate, leukocytosis with neutrophilia is an infrequent side effect of infliximab infusions.Unique to our case is that the patient did not have a clinical infusion reaction.This phenomenon may have an association to the development of autoantibodies to infliximab despite the lack of an acute infusion reaction or a delayed hypersensitivity reaction.