An 85-year-old woman was admitted to our hospital because of leukocytosis. Abnormal lymphocytic leukocytosis, including few plasmacytes, anemia, and thrombocytopenia, were observed. A diagnosis of primary macroglobulinemia was made based on immunoglobulin M-kappa monoclonal gammopathy, FACS of abnormal lymphocytes, and confirmed MYD88 L265P somatic mutation. Abnormal lymphocytes were markedly increased temporarily after the administration of tirabrutinib. However, the patient continued treatment after abdominal computed tomography showed that splenomegaly and lymphadenopathy had improved, and the patient recovered from leukocytosis. There are no reports that leukocytosis is a side effect of tirabrutinib; therefore, this case can be considered unique.
Keywords: Leukocytosis; Primary macroglobulinemia; Tirabrutinib.