Increased Mast Cell Numbers in Bone Marrow of Patients with Myeloproliferative Neoplasms and Pruritus.

Pruritus may be a debilitating symptom in cases of myeloproliferative neoplasm (MPN). Since mast cells (MCs) play a pivotal role, we hypothesized that bone marrow (BM) MCs contribute to the occurrence of pruritus. In this exploratory study, untreated MPN patients were included. BM aspirate/biopsy/blood samples and responses to the MPN-Symptom Assessment Form were obtained. Thirty-two patients were included (essential thrombocythemia, n=19; polycythemia vera, n=7; primary myelofibrosis, n=6). Eleven had clinically significant pruritus (35%). The absolute MC count and proportion per total nucleated BM cells were significantly higher in patients with pruritus compared to those without (mean of 25.5 vs. 58.1 MCs/mm2, p=0.032 and 0.59% vs. 1.66%, p=0.041, respectively). MC immunophenotypes and serum levels of tryptase, interleukin-6, tumor necrosis factor alpha, and soluble CD117 were not correlated. Thus, this study showed that absolute and relative MC numbers are increased in cases of MPN with pruritus. However, whether MCs play a pathophysiological role in causing pruritus or are bystanders remains to be determined.