A man with a deltoid swelling and paraneoplastic erythrocytosis: case report.

Erythrocytosis is a well-known paraneoplastic syndrome occurring in 1% of cancer cases. Herein, we report a patient with a history of renal cell carcinoma (RCC) who developed a paraneoplastic erythrocytosis 3 months after curative nephrectomy. Concomitantly we documented the presence of a deltoid mass, highly suggestive for a muscle metastasis. The most important features found in this patient were: 1) the absence of erythrocytosis at the time of diagnosis, 2) the high concentration of haemoglobin and hematocrit, with no increase in serum erythropoietin (Epo) level at the time of RCC relapse. Metastasectomy was performed and hemoglobin and hematocrit returned to normal range after the operation. Even in the absence of immunohistochemical and biomolecular evidence of Epo production in the neoplastic tissue, we think the hypothesis of paraneoplastic syndrome may be the most likely, both for the strict temporal relationship between the observation of the neoplastic lesion and the appearance of polycythemia and for the absence of all other known causes of erythrocytosis. An objection to this hypothesis was the ectopic production of an Epo-like factor. The English language literature about muscle metastases and paraneoplastic erythrocytosis was reviewed.