A case of chronic myelomonocytic leukemia complicated with spondyloarthritis.

Chronic myelomonocytic leukemia (CMML), a clonal hematopoietic stem cell disorder with myelodysplastic and myeloproliferative overlap feature, is frequently associated with autoimmune diseases, such as vasculitis, polyarthritis, and neutrophilic dermatosis. We herein report the first case of CMML complicated with spondyloarthritis (SpA). A 64-year-old female patient, admitted to our hospital with buttock pain alternating left and right, was found to have sacroiliitis and spondylitis by contrast magnetic resonance imaging. Peripheral blood test and bone marrow biopsy revealed an increase of monocytes with trilineage dysplasia. We made a diagnosis of CMML. Although arthritic symptoms and imaging findings initially improved by azacitidine, CMML was thereafter transformed into acute myeloid leukemia. She is scheduled to hematopoietic stem cell transplantation. The concomitant onset of sacroiliitis with CMML suggested that her SpA feature was a paraneoplastic phenomenon of CMML. Thus, we must be aware that myelodysplastic syndrome including CMML can manifest as SpA.