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

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.