Paraneoplastic hypercalcemia in a dog with benign renal angiomyxoma.

An 11-year-old, male, neutered crossbred Collie dog was presented for a history of polydipsia and polyuria. Diagnostic investigations revealed total and ionized hypercalcemia and an increased concentration of parathyroid hormone-related peptide. Abdominal ultrasonography and contrast-enhanced computed tomography of the abdomen revealed a right-sided, cystic-appearing renal mass. Cytological examination of ultrasound-guided aspirates of the mass revealed high numbers of spindle cells. The mass was removed en bloc via an ureteronephrectomy. Histopathological examination of the mass revealed neoplastic spindle cells in loosely packed and interlacing streams within a myxomatous stroma. Immunohistochemical examination with vimentin, von Willebrand Factor, and alpha-smooth muscle actin confirmed the mass to be a renal angiomyxoma. A minority of the neoplastic spindle cells showed positive cytoplasmic parathyroid hormone-related peptide immunostaining. The hypercalcemia resolved following surgery, and the parathyroid hormone-related peptide concentration returned to within the reference interval. The dog was no longer polydipsic or polyuric 1 year following surgery. The present report describes a previously unreported renal neoplasm causing paraneoplastic hypercalcemia and highlights the possibility of paraneoplastic hypercalcemia being caused by a benign neoplasm.