Risk factors for urolithiasis in dogs with congenital extrahepatic portosystemic shunts: 95 cases (1999–2013)

• Autores: Evelyn H. G. Caporali
• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 246, Nº. 5, 2015, págs. 530-536
• Idioma: inglés
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• Resumen

  • Objective—To identify risk factors for urolithiasis in dogs with congenital extrahepatic portosystemic shunts (EHPSSs) and to determine whether portoazygos shunts were associated with increased risk of urolithiasis at the initial evaluation for EHPSS.

    Design—Retrospective case series.

    Animals—Dogs (n = 95) with EHPSSs confirmed via CT angiography or surgery.

    Procedures—Medical records from 1999 to 2013 were reviewed. Variables of interest included signalment, previous medical management, and results of urinalysis, urolith analyses, and diagnostic imaging. Univariable and multivariable logistic regression analyses for assessment of risk factors for urolithiasis at the time of initial EHPSS evaluation were performed.

    Results—The dogs’ median age was 0.9 years (range, 0.2 to 12.6 years). Among the 95 dogs, 27 (28.4%) and 68 (71.6%) had portoazygos and portocaval shunts, respectively. Urinalysis was performed for 79 (83.2%) dogs, 29 (36.7%) of which had crystalluria (mainly ammonium urate and struvite crystals). Uroliths were present in 34 of 95 (35.8%) dogs; 16 of 17 uroliths analyzed were composed of ammonium urate. Portoazygos shunts were not associated with significantly increased odds of urolithiasis at the time of the initial evaluation for EHPSS. However, the odds of urolithiasis was significantly increased for male dogs, older dogs, and dogs that received previous medical treatment.

    Conclusions and Clinical Relevance—In dogs with EHPSS, shunt morphology was not associated with increased odds of urolithiasis at the initial evaluation. Male dogs, older dogs, and dogs having received medical management for EHPSS prior to initial evaluation should be considered at increased risk for development of urolithiasis.

    Since the first report of PSSs in dogs in 1974,1 a great amount of research on this condition has been conducted. Most research has assessed methods of PSS diagnosis,2–8 shunt classification,9,10 treatment options and outcomes,11–14 and identification of genetic predisposition.15,16 Portosystemic shunts can be acquired or congenital. Acquired PSSs develop most often secondary to chronic portal hypertension.17 Congenital PSSs can be extrahepatic or intrahepatic.17,18 Congenital single EHPSSs are frequently identified in small purebred dogs.19–22 The portal vein provides 80% of the blood supply to the liver.23 In dogs with an EHPSS, the portal circulation communicates directly with the systemic circulation; this shunt deprives the liver of its blood supply and results in the organ's poor development.1 Several PSS morphologies have been described, with the shunting vessel originating from the portal, splenic, right gastric, left gastric, left gastroepiploic, pancreaticoduodenal, or cranial or caudal mesenteric veins and terminating on the azygos vein or caudal vena cava.9,10,17,24 In dogs with EHPSS, clinical signs develop secondary to impaired liver function and most commonly involve the CNS and gastrointestinal and urinary tracts.19,25–27 Marretta et al28 first reported concurrent ammonium urate urolithiasis in a series of 6 dogs with PSSs. Since then, retrospective studies19,21,25,29,30 of dogs with PSSs have found a prevalence for urolithiasis at the time of PSS diagnosis of 11% to 58%. The most commonly identified urolith type is ammonium urate.29,30 To the authors’ knowledge, there are no reports describing the risk factors for urolithiasis in dogs with PSSs. The main objective of the study reported here was to describe risk factors for urolithiasis in dogs at the time of initial evaluation of congenital EHPSSs. Studies21,22,31 have shown that portoazygos shunts are usually diagnosed in older dogs. Moreover, it has been suggested that portoazygos shunts have a smaller shunt fraction due to the smaller diameter of the recipient vessel and shunt compression during respiration,8,22,31 which results in milder clinical signs and a delay in the diagnosis of EHPSS.32 Considering that uroliths may take time to form, we hypothesized that compared with portocaval shunts, portoazygos shunts would be associated with increased risk of urolithiasis at the time of initial evaluation of dogs with EHPSSs.