Xanthine Urolith in a Dog with Visceral Leishmaniasis Treated with Allopurinol

Abstract

Background: Xanthine urolithiasis is a rare condition in dogs, with a prevalence of less than 1% of cases. Its etiology has not yet been fully understood in this species, and it has been suggested as primary (or hereditary) and secondary (or iatrogenic) to the use of drugs with potential to inhibit the enzyme xanthine oxidase, which is responsible for the transformation of xanthine and hypoxanthine and formation of uric acid, as well as allopurinol, a drug widely used in the treatment of canine visceral leishmaniasis. The aim of the present study was to report the clinical and diagnostic aspects of a case of xanthine urolithiasis in a dog with visceral leishmaniasis receiving low doses of allopurinol.

Case: A 2-year-and-2-month-old male German Shepherd dog with a body mass of 32.2 kg was treated for visceral leishmaniasis using miltefosine (2 mg/kg, once daily) for 28 days, domperidone (0.94 mg/kg, once daily) for 30 days, and allopurinol (9.49 mg/kg, twice daily) uninterrupted for 140 days and presented with stranguria and polyuria. During the consultation, a urinary obstructive condition caused by numerous small stones was identified, and the patient was submitted to imaging exams after clearance, which showed a hyperechoic spherical structure associated with acoustic shading, measuring 0.96 cm × 0.66 cm, also seen radiographically in the region of the urinary bladder, with radiopacity similar to soft tissues, suggestive of urolithiasis. Surgical removal of the urolith was performed via cystotomy, and the specimen was sent for mineralogical analysis. It was characterized as a greenish-brown material composed of 90% xanthine and 10% ammonium urate. The patient had been under constant clinical follow-up before the obstructive condition and had ultrasound results of 3 months before the event, or 80 days after starting treatment with allopurinol, with no significant findings in the urinary bladder. After confirmation of the diagnosis of bladder urolithiasis due to xanthine and considering the history of allopurinol use, stone formation was considered iatrogenic in this case. The therapeutic approach was the suspension of allopurinol and feed management with low-protein dry food to reduce the number of purines of food origin, in addition to clinical, ultrasound, radiographic, and hematologic follow-up of the patient for 6 months after the interruption of the drug, and there were no signs of recurrence of the condition.

Discussion: The rate at which the urolith developed was surprising because the dog was submitted to allopurinol therapy for only 140 days, unlike most reported cases in which the animals receive treatment for long periods, usually years, until the identification of xanthine urolithiases. A few reports mention stone formation after a short period of allopurinol use, but they do not present screening imaging exams performed before the beginning of treatment, which does not allow ruling out the existence of changes before the use of allopurinol. It can be concluded that the formation of xanthine uroliths should be considered in the differential diagnosis of dogs treated with allopurinol, even for short periods of time, regardless of the dosage used, and that ultrasound and radiographic exams performed before the initiation of medication and regularly during its use are very important for early intervention.

Keywords: CVL, small animal medical clinic, urolithiasis, xanthinuria, zoonosis.

Título: Urólito de xantina em um cão com leishmaniose visceral sob administração de alopurinol

Descritores: LVC, clínica médica de pequenos animais, urolitíase, xantinúria, zoonoses.