Masked Triple-Negative Polycythemia Vera Initially Presenting as Iron Deficiency and Pernicious Anemia

Polycythemia vera (PV) is a myeloproliferative neoplasm characterized by erythrocytosis, typically driven by JAK2 mutations. Diagnosis can be challenging when concurrent conditions mask the underlying erythrocytosis. Iron deficiency is the most common masking factor; however, to the authors' knowledge, this is the first reported case in which the combination of iron deficiency and pernicious anemia created a dual masking mechanism. A 68-year-old Hispanic female patient with a history of chronic anemia presented with severe symptomatic anemia requiring transfusion (hemoglobin 5.2 g/dL). Evaluation revealed iron deficiency anemia and pernicious anemia secondary to autoimmune gastritis, confirmed by positive intrinsic factor and anti-parietal cell antibodies. Following intravenous iron and intramuscular vitamin B12 repletion, hemoglobin normalized. However, the patient subsequently developed progressive erythrocytosis, with hemoglobin rising to 19.8 g/dL and hematocrit to 58.7%. Evaluation revealed suppressed erythropoietin (2.1 mIU/mL), negative molecular testing for JAK2, CALR, and MPL mutations, and exclusion of secondary causes. Repeat bone marrow biopsy demonstrated marked hypercellularity with trilineage panmyelosis and clusters of enlarged pleomorphic megakaryocytes with hyperlobulated nuclei, establishing the diagnosis of JAK2-unmutated PV. This case illustrates a rare presentation of masked PV in which concurrent iron deficiency and pernicious anemia from autoimmune gastritis simultaneously obscured the underlying myeloproliferative process. The dramatic hemoglobin swing from 5.2 g/dL to 19.8 g/dL, observed during clinical follow-up after correction of the iron and vitamin B12 deficiencies, served as the key diagnostic clue. Clinicians should maintain vigilance for underlying myeloproliferative neoplasms when erythrocytosis develops following correction of nutritional deficiencies, even in the absence of canonical driver mutations. In JAK2-unmutated cases, bone marrow morphology becomes the cornerstone of diagnosis.