Association of primary myeloperoxidase deficiency and myeloproliferative neoplasm.

We report a 63-year-old woman with myeloproliferative neoplasm (MPN), who presented with inflammatory involvement of the skin. The white cell count was 31,800/μL and the platelet count was 709×10/μL. The positivity of neutrophil alkaline phosphatase was 100% and the score was 281. The bone marrow was hypercellular with enlarged megakaryocytes with mature cytoplasm and multilobulated nuclei (Picture 1A; May-Giemsa staining, ×40 objective). The myeloid-lineage cells contained coarse toxic granules (Picture 1B; May-Giemsa, ×100), probably reflecting the cutaneous complication, while they were entirely negative for peroxidase activity except for eosinophils (Picture 1C; peroxidase staining, ×100). Peripheral blood pictures confirmed the lack of activity of monocytes (Picture 1D; peroxidase, × 100). On the other hand, the periodic acid-Schiff reaction and naphthol AS-D chloroacetate esterase positivity of neutrophils as well as the α-naphthyl butyrate esterase positivity of monocytes were normal. The patient has been treated with hydroxyurea for cytoreduction. Primary myeloperoxidase (MPO) deficiency is caused by