TY - JOUR T1 - Acquired Erythrocytosis Upon Treatment with Infliximab for Ankylosing Spondylitis JF - The Journal of Rheumatology JO - J Rheumatol SP - 581 LP - 583 DO - 10.3899/jrheum.101013 VL - 38 IS - 3 AU - MARIA ANTONELLI AU - MANOJKUMAR BUPATHI AU - MURALI JANAKIRAM AU - PAUL HERGENROEDER AU - MUHAMMAD ASIM KHAN Y1 - 2011/03/01 UR - http://www.jrheum.org/content/38/3/581.abstract N2 - To the Editor:We describe a patient with ankylosing spondylitis (AS) who was treated with infliximab and developed polycythemia that was Janus kinase 2 (JAK2)-negative (V617F and exon 12 mutation). This is the first report of a patient with AS that developed erythrocytosis on treatment with infliximab.A 31-year-old man of Italian and German ethnicity with HLA-B27-positive AS was started on treatment with infliximab (5 mg/kg dose) in May 2007 because of lack of response to nonsteroidal antiinflammatory drugs. The disease showed excellent response to infliximab. He had a 15-pack-year smoking history. Prior to starting infliximab, in April 2007 his hemoglobin was 14.5 g/dl, hematocrit 45.5%, and platelet count 334 x 103/μl. He gradually developed erythrocytosis (June 2008) with hemoglobin 20.3 g/dl, hematocrit 56.6%, and platelet count 218 x 103/μl, and was referred to the hematology clinic in July 2008. His peripheral blood smear was noted to be benign. Jak2 mutation was negative including exons 12/14, and erythropoietin level was normal. Bone marrow biopsy revealed erythroid hyperplasia and a mild increase in reticulin staining. He was started on aspirin and therapeutic phlebotomies until his hematocrit decreased to 43.6%, and it has remained below 45% after 12 months of phlebotomies with continued treatment with infliximab.Polycythemia is suspected in men when hematocrit rises above 52% or hemoglobin concentration above 18.5 g/dl; the corresponding values for women are … Address correspondence to Dr. M. Antonelli, Department of Rheumatology, MetroHealth Medical Center, 2500 MetroHealth Drive, Cleveland, OH 44109. E-mail: mantonelli{at}metrohealth.org ER -