The pseudo-Pelger-Huët anomaly in pyoderma gangrenosum associated with myelodysplastic syndrome.

We report a case of pyoderma gangrenosum in which most of the neutrophils exhibited the pseudo-Pelger-Huët (pPH) anomaly, a cytologic abnormality affecting the neutrophil nucleus. Pelgeroid cells have round, oval, or hyposegmented nuclei and are therefore difficult to recognize as neutrophils. The pPH anomaly is important because it is found mostly in patients with myelodysplastic syndromes or myeloid leukemias. These patients are also at risk for developing neutrophilic dermatosis as well as leukemia cutis, the main differential diagnosis. In our case, the proper diagnosis was made with the help of immunohistochemistry.