Sweet's syndrome evolved from recurrent erythema nodosum in a patient with myelodysplastic syndrome

A 63-year-old man had painful nodules on his lower legs. Microscopic examination showed septal and lobular panniculitis composed of lympho-histiocytic infiltrates. Based on the clinical and histopathological findings, the diagnosis of erythema nodosum (EN) was made. Nonsteroidal anti-inflammatory drugs were temporarily effective, but the eruptions had repeated to the present, and 16 months later, myelodysplastic syndrome (MDS) was diagnosed. Then, 6 months later, he developed a high fever and edematous fresh red-colored nodules on his neck, arm and upper trunk. Histopathologically, a diffuse, dense, dermal infiltrate of neutrophils was seen, and Sweet's syndrome (SS) was diagnosed. SS is known to develop in patients with MDS, and EN is one of the dermatoses that occur in conjunction with hematoproliferative disorders. Furthermore, SS evolving from recurrent EN and the simultaneous occurrence of SS and EN have been reported in some patients. In our case, we suggest that some mediators such as cytokines associated with MDS might have first induced EN, and then, as the MDS developed, they were replaced by others that caused SS.