Splenic histopathological patterns in chronic myelomonocytic leukemia with clinical correlations: Reinforcement of the heterogeneity of the syndrome

The syndrome of chronic myelomonocytic leukemia (CMML) includes a heterogeneous group of patients who exhibit both myelodysplastic and myeloproliferative clinicopathological features. Troublesome splenomegaly is uncommon in myelodysplastic syndrome (MDS), but when organomegaly occurs, this complication is more likely to be associated with myelodysplastic-myeloproliferative overlap syndromes such as CMML rather than "dysplasia-only" MDS types such as refractory anemia. We report a single-institution experience with splenectomy in CMML patients, including a detailed review of splenic histopathology. Twelve patients with CMML underwent splenectomy at the Mayo Clinic, primarily because of refractory thrombocytopenia and/or mechanical complications related to splenomegaly. Three of the 12 patients (25%) died as a direct result of surgery, and significant postoperative morbidity was seen in another 4 patients (33%). Thrombocytopenia improved in 4 of the 11 patients (36%) with low platelet counts before surgery. Three of the four responders had an abundance of CD68 (PGM1)-positive foamy histiocytes in the marginal zone surrounding the splenic white pulp - a pattern which can be seen in immune thrombocytopenia - and two of these three patients had thrombocytopenia out of proportion to the degree of anemia pre-operatively, suggestive of peripheral destruction of platelets. More consistent splenic pathological findings in the 12 patients included trilineage extramedullary hematopoiesis in splenic red pulp and expansion of splenic cords by a myelomonocytic infiltrate. This study underscores both the uniformity and diversity of splenic findings in CMML, highlights the potential dangers and benefits of splenectomy in this group, and suggests peripheral destruction of platelets as a mechanism contributing to thrombocytopenia in a subset of CMML patients.