Polycythemia with elevated erythropoietin production in a patient with a urinary stone and unilateral hydronephrosis: a case report

BACKGROUND: Absolute polycythemia can be primary or secondary. Erythropoietin-producing diseases (for example, hypoxia) are the major cause of secondary polycythemia. There are reports of polycythemia secondary to hydronephrosis. However, to our knowledge, there is no report on polycythemia secondary to hydronephrosis due to a urinary stone. Herein, we present a case of polycythemia with an elevated erythropoietin level in a patient with a urinary stone and unilateral hydronephrosis. CASE PRESENTATION: A 57-year-old Japanese man presented with polycythemia and an elevated erythropoietin level. Erythropoietin accumulation was not due to erythropoietin secretion by a tumor as no obvious lesions were detected on contrast-enhanced computed tomography. Abdominal ultrasonography revealed a stone in the left urinary tract and renal hydronephrosis, and 2 weeks later, the patient underwent transurethral ureterolithotripsy without complications. Blood tests 2 weeks after transurethral ureterolithotripsy showed that the erythropoietin level had declined. Hemoglobin concentration decreased from 20.8 mg/dL before and immediately after transurethral ureterolithotripsy to 15.8 mg/dL 3 months after transurethral ureterolithotripsy. This case was diagnosed as erythropoietin elevation due to unilateral hydronephrosis with a urinary stone, resulting in polycythemia. CONCLUSIONS: Hydronephrosis is a common disease but is not often associated with polycythemia. Further studies are required to elucidate the mechanism and implications of elevated erythropoietin production in hydronephrosis.