Sweet's syndrome with Koebner phenomenon triggered by G-CSF as a preleukemic manifestation in a patient with primary myelofibrosis: a case report.

Background: Sweet's syndrome (SS), also known as acute febrile neutrophilic skin disease, is a rare inflammatory skin disease. Clinically, patients often have fever and leukocytosis, characterized by painful erythema, papules or pustules. According to different etiologies, SS can be classified into three types: idiopathic, tumor-related and drug-induced. Among them, tumor-associated SS is closely related to some hematological malignancies. Drug-induced SS, on the other hand, can be induced by the use of granulocyte colony-stimulating factor (G-CSF). Case introduction: This article reports a 42-year-old male patient who was admitted to the hospital due to "significant splenomegaly and splenic stasis." After admission, the patient was diagnosed with primary myelofibrosis through examination. During the hospitalization process, the patient received G-CSF treatment and open total splenectomy. On the 8th day after subcutaneous injection of 100 μg of G-CSF, erythema, swelling and superficial ulcers occurred at the surgical incision and drainage site, accompanied by Koebner's phenomenon. The results of skin biopsy indicated Sweet's syndrome. The rash improved significantly and rapidly several days after intravenous application of methylprednisolone. However, several months after discharge, the patient was diagnosed with acute myeloid leukemia through bone marrow puncture in another hospital and unfortunately passed away due to the progression of the disease. Conclusion: Among patients with complex underlying diseases such as myelofibrosis and receiving G-CSF treatment, Sweet's syndrome may not only be an adverse reaction caused by drugs, but more likely to be an early manifestation of leukemia. At this time, SS is a complex comprehensive disease caused by multiple factors. It is not advisable to simply diagnose its phenotype. Instead, a comprehensive assessment should be conducted to reduce misdiagnosis and missed diagnosis. Therefore, in clinical practice, we should strengthen multidisciplinary collaboration even more and enhance the understanding of Sweet's syndrome itself and its role as a potential early warning signal of leukemia. This enables the early identification of diseases and the adoption of effective treatment measures. Although the Koebner phenomenon is relatively rare in SS, its occurrence should be highly valued.