In August 2021, a 74-year-old Japanese woman was referred to our hospital for leukocytosis that occurred for the past one year. The patient denied pruritus, visual disturbance, or palmar erythema. Her complete blood count parameters were as follows: white blood cells, 14600/μL; red blood cells, 5.66 x 10⁶/μL; hemoglobin, 10.5 g/dL; mean corpuscular volume, 63.3 fL; platelets, 739 x 10³/μL; ferritin, 3.1 ng/mL. Upper gastrointestinal endoscopy and colonoscopy showed no abnormal findings. We suspected iron deficiency anemia (IDA), and oral iron supplementation was started. In November 2021, hemoglobin levels improved to 16.4 g/dL, but leukocytosis and thrombocytosis remained unchanged. Physical examination revealed flushing of the skin on her hands, but without pain or dysesthesia (Figure 1). Additional laboratory tests showed erythropoietin levels of 0.7 mIU/mL (reference value 4.2–23.7), and a mutation was identified at a novel Janus kinase 2 (JAK2) gene. The patient was positive for anti-Helicobacter pylori antibodies. She was then referred to a hematologist, and bone marrow biopsy revealed hyperplasia with megakaryocytes. Polycythemia vera (PV) with IDA was diagnosed. Hydroxyurea, phlebotomy, and aspirin was continued for the treatment of PV.

PV is one of the chronic myeloproliferative diseases characterized by an increased red cell mass on normal hemoglobin oxygen saturation, and affected individuals may have elevated white blood cell and platelet counts.¹ This condition is characterized by fatigue and pruritus, along with an increased risk of thrombosis.² There have been reports of PV combined with IDA, which can mask diagnosis and delay treatment because of the anemic presentation.¹ Several possibilities for the pathogenesis of IDA associated with PV have been proposed as follows³: decreased expression of erythroferrone (ERFE), activation of JAK/STAT, decreased iron absorption, or complications of gastrointestinal bleeding. Gastroduodenal lesions and the presence of Helicobacter pylori are more commonly found in PV patients than in the general population,⁴ and may be related to gastrointestinal bleeding and decreased iron absorption. In the case of PV combined with IDA, the diagnosis may be delayed due to the lack of symptoms, in addition to the presence of anemia in blood tests. In this case, palmar erythema appeared during the treatment of iron deficiency anemia, which eventually led to the diagnosis of masked PV due to IDA.