Een massa in de knieholte en leukocytose door een paraneoplastische leukemoïde reactie

A 65-year-old woman was referred with a mass in the right popliteal fossa, fever and leucocytosis reaching 105 x 10 9 /l. Her medical history included the excision of a melanoma from the right ankle more than 20 years before. Ultrasound, CT and positron-emission tomography showed the mass in the right knee but no other lesions. The process was drained. Histological examination of a subcutis biopsy indicated malignancy. Due to deterioration in her clinical condition amputation of the right leg was performed after which her leucocyte count normalized. The pathology specimen revealed a high-grade undifferentiated soft tissue tumour of unclear origin. Preoperatively assessed serum levels of granulocyte-stimulating factor (G-CSF), interleukin 6 and interleukin 8 were elevated to 241, 91 and 82 pg/ml respectively. After the amputation these levels returned to almost normal. This extreme leucocyte count may be explained by a paraneoplastic leukemoid reaction. It is hypothesized that the tumour cells produce G-CSF and other cytokines causing leucocytosis. Normalisation of the cytokine levels postoperatively supports this hypothesis.