Bilateral ureterolithiasis in a 7-month-old cat

: Feline ureteral obstruction can have several causes; however, ureterolithiasis has been increasing in occurrence. The restriction of urinary flow induced by the obstruction has harmful consequences to the body and can lead to acute renal failure. Calcium oxalate ureterolithiasis is reported in older cats, aged mean 12 years old. A case of bilateral ureteral obstruction in a 7-month-old mixed breed cat is described in this report. Imaging tests such as abdominal ultrasonography, radiography and excretory urography were performed to determine the diagnosis. The surgical procedure of bilateral ureterotomy was then performed, which allowed the improvement of the urinary flow of both kidneys and the resolution of clinical signs caused by uremia. The quantitative analysis of both uroliths revealed the composition of 100% monohydrate calcium oxalate. Calcium oxalate stones can also cause ureteral obstruction in young cats; although, are less common in this age. When conservative treatment fails, surgical intervention becomes necessary for the rapid return of renal function. To author’s knowledge this is the first report of a ureterolithiasis caused by calcium oxalate in a young cat. words

This reported the occurrence and surgical treatment of bilateral ureteral obstruction due to calcium oxalate stones in a 7-month-old mixed breed cat ( Figure 1A), treated at the Feline Medicine Service of the Veterinary Clinic Hospital of the Federal University of Rio Grande do Sul. The owner reported that the animal presented signs of abdominal pain, halitosis, anorexia, and prostration for five days. The cat was feeding dry food. Abdominal palpation revealed a bilateral renal enlargement, in addition to abdominal pain. Blood tests revealed severe azotemia with a creatinine value of 8.91 mg/dL (reference 0.8-1.6 mg/dL). Abdominal ultrasound examination showed bilateral hydronephrosis, hydroureter and pyelectasia. The left kidney presented regular contour, while the right kidney was irregular and had anechoic fluid between the kidney and the renal capsule. The fluid was collected and the analysis was compatible with urinary leakage, determined by comparing the fluid creatinine of 37.09 mg/dL with the serum creatinine of 8.91 mg/dL. The cat showed polyuria, and urinary density was low (1.008 reference 1.025 -1.060) denoting isosthenuria. Excretory urography was performed and showed bilateral renomegaly, but the nephrogram and pyelogram were not clearly observed, indicating bilateral deficiency in renal filtration. During hospitalization, the patient received fluid therapy with lactated Ringer's solution at a rate of 60 mL/kg/day, methadone (0.2 mg/kg TID SC) amitriptyline (2 mg/kg SID PO) and dipyrone (25 mg/kg BID IV).
However, as there was no clinical improvement after two days of conservative treatment (creatinine value increased to 10.14 mg/ dL), the patient was referred to an exploratory laparotomy, followed by bilateral ureterotomy to remove small stones located in both ureters ( Figure  1B). After the surgical procedure, the patient showed clinical improvement. Bilateral pyelectasis decreased and;consequently, bilateral hydronephrosis on imaging studies. Creatinine values normalized four days after the surgical procedure (1.3 mg/dL), and the patient was discharged home after six days of hospitalization.
The uroliths ( Figure 1C) were sent to the Minnesota Urolith Center (University of Minnesota, USA) where they underwent quantitative analysis by polarized light microscopy and infrared spectroscopy techniques, which revealed the composition of both stones of 100% monohydrate calcium oxalate.
After 60 days of the hospital admission, the patient returned to the hospital for reassessment and remained without clinical signs. Abdominal ultrasonography revealed a small accumulation of subcapsular fluid in the right kidney, but there were no alterations in both renal pelvises and medullary region.
Ureterolithiasis is the main cause of ureteral obstruction in felines, and calcium oxalate is the most often stone found (ZAID et al., 2011). Conservative management include treatment with fluid therapy, continuous infusion of mannitol, amitriptyline, alpha-adrenergic blockers (prazosin) and glucagon (CLARKE, 2018a). In humans, more than 98% of small diameter ureteral stones (≤ 5 mm) pass spontaneously up to the bladder, and the treatment consists mainly in treatment of pain relief (SEGURA et al., 1997). In cats, due to the small size of the ureter, which measures 0.4 mm in internal diameter, the spontaneously passage of stones is not so frequent as in humans. A study reported that 30% of cats had a significant reduction in azotemia after conservative treatment (KYLES et al., 2005). The decision for surgical removal must be made with caution, as complications of this type of intervention are common (KOCHIN et al., 1993). The postoperative mortality rate varies between 16 and 21% (KYLES et al., 1998;KYLES et al., 2005;ROBERTS et al., 2011). In the case described, the surgical indication was given after an attempt of conservative treatment with amitriptyline, analgesics and fluid therapy. However, as the young cat had a bilateral obstruction, the time for surgical decision had to be shortened to when it was noticed that there was no clinical improvement with conservative management. In order to avoid the urolith's recurrence, the owner was advised to increase the cat's water intake, offering wet food and enhancing water resources. There is a risk of re-obstruction in about 22% of the reported cases, so the owner should be advised about the need for additional procedures and periodical monitoring (CLARKE, 2018b). Ureteral obstruction by stones are more common in older animals. A study reported a median age of 12 years old in affected animals, with the youngest animal being 5 years old. Most obstructions in young cats are due to congenital malformation (ZAID et al., 2011). The case described is uncommon since the affected cat was only seven months old.
Although, reports of calcium oxalate urolithiasis are more frequent in adult cats, young cats can also present the disease. This type of urolith occurs when urine is oversaturated with calcium and oxalate. Aciduria is also a risk factor and genetic anomalies may be involved (BARTGES & CALLENS, 2015). When medical treatment for ureteral obstruction does not resolve the obstruction, surgical intervention is imperative for the restoration of renal function (CLARKE, 2018a).
Calcium oxalate urolithiasis must be a differential diagnosis for ureteral obstruction, even in young cats. Clinical signs such as acute abdominal pain associated with azotemia should be considered during clinical investigation. Conservative management can be tried, but if there is lack of improvement in clinical signs, ureterotomy should be performed. Veterinarians should pay attention to the incidence of this disease and occurrence in younger cats.

ACKNOWLEDGMENTS
This study was financed in part by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (Grant number 131701/2018-5). And was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasil -Finance code 001.

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