Increased Mast Cell Numbers in Bone Marrow of Patients with Myeloproliferative Neoplasms (MPN) and Pruritus

Pruritus might be a debilitating symptom in myeloproliferative neoplasms (MPN). Since mast cells (MC) play a pivotal role, we hypothesized that bone marrow (BM) MC contribute to the cause of pruritus. In this exploratory study, untreated MPN patients were included. BM aspirate/biopsy/blood and MPN-SAF questionnaires were obtained. Thirty-two patients were included (Essential Thrombocythemia n=19, Polycythemia Vera n=7 and Primary Myelofibrosis n=6). Eleven had clinically significant pruritus (35%). The absolute MC count and proportion/total nucleated BM-cells were significantly higher in patients with pruritus compared to those without (mean 25.5 vs. 58.1 MC/mm2, p 0.032, and 0.59 vs 1.66%, p 0.041, respectively). The MC immunophenotype and serum levels of tryptase, IL-6, TNF-α and sCD117 were not correlated. The absolute and relative MC numbers are increased MPN patients with pruritus. Whether MC play a pathophysiological role in causing pruritus, or are bystanders remains to be determined.