Severe unilateral nephrolithiasis and recurrent colic in a horse

Urolithiasis is an uncommon disorder reported in horses. Calculi located in the kidneys and ureters are often underdiagnosed. Associated clinical signs include weight loss, anorexia, haematuria, dysuria, colic and polyuria/polydipsia. A 26-year-old Thoroughbred gelding was referred for evaluation of an acute colic episode of 5-hour duration. Haematologic analysis revealed increased serum creatine kinase and creatinine concentrations. Abdominocentesis yielded serosanguineous, mildly cloudy fluid with a lactate of 9.6 mmol/L (<2 mmol/L). Exploratory laparotomy was recommended. Surgical intervention was declined, and the horse was humanely euthanased. Limited postmortem evaluation was performed. A 3.633 kg nephrolith measuring 23.6 x 16.2 x 8.9 cm was completely effacing the left kidney. Crystallography and infrared spectroscopy (attenuated total reflection and Fourier transform infrared) revealed a 100% calcium carbonate nephrolith. Carbonate calcium calculi are the most common subtype in horses. Nephrolithiasis should be considered as a differential diagnosis for colic and haematologic evidence of azotaemia in horses.