Tofacitinib Use in a Patient With Rheumatoid Arthritis and Polycythemia Vera: A Case Report.

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation and joint destruction, whereas polycythemia vera (PV) is a myeloproliferative neoplasm driven by the Janus kinase (JAK)2 V617F mutation, resulting in erythrocytosis and increased thromboembolic risk. Although JAK inhibitors are established in rheumatology, most selectively inhibit JAK1 and JAK3, sparing JAK2 activity, which is central to PV pathogenesis. We describe a 61-year-old woman with seropositive RA and JAK2 V617F-positive PV. Treatment for polycythemia vera included hydroxyurea. Methotrexate and sulfasalazine were prescribed for rheumatoid arthritis but were withdrawn due to intolerance, and therapy was switched to tofacitinib 5 mg twice daily. Within 3 months, she achieved clinical and ultrasonographic remission of RA, with improvement of inflammatory markers. Hematologic parameters remained stable throughout follow-up. After 6 months, a mild improvement allowed reduction in hydroxyurea dosing, although further tapering resulted in recurrence of erythrocytosis. After 12 months of therapy, RA remission persisted without adverse events or cytopenias. Tofacitinib demonstrated rheumatologic efficacy but minimal effect on PV-related hematologic activity.