Atypical neutrophilic panniculitis as presentation of BCR-ABL1-negative chronic myeloid leukaemia.

We report the case of an otherwise healthy 60-year-old man presenting with fever, leucocytosis and a painful swelling of the right calf. We initially performed cultural and cytological examination of the popliteal fossa mass, but the results were disappointingly inconclusive. The subsequent development of several erythematous subcutaneous nodules, rapidly evolving to broad ulcerative lesions, prompted us to reconsider the clinical setting as a whole, which included fever, marked leucocytosis and multiple subcutaneous nodules. A biopsy of the ulcerative lesions finally led to the diagnosis of neutrophilic panniculitis, which was sustained by a hybrid myelodysplastic/myeloproliferative disorder like BCR-ABL1-negative atypical chronic myeloid leukaemia. The patient was initially treated with high-dose intravenous corticosteroids, resulting in a dramatic improvement of the skin lesions and normalisation of blood tests. Azacytidine treatment was subsequently started, and the haematological disease remained stable.