Nephrotic syndrome in dogs: clinical features and evidence-based treatment considerations

Nephrotic syndrome (NS), defined as the concurrent presence of hypoalbuminemia, proteinuria, hyperlipidemia, and fluid accumulation in interstitial spaces and/or body cavities, is a rare complication of glomerular disease in dogs, cats, and people. Affected animals frequently have markedly abnormal urine protein:creatinine ratios because of urinary loss of large amounts of protein; however, hypoalbuminemia-associated decreased plasma oncotic pressure is insufficient to explain fluid extravasation in most laboratory models, and, instead, either aberrant renal tubule retention of sodium with resultant increase in hydrostatic pressure or a systemic increase in vascular permeability may be the primary defects responsible for development of NS. Factors associated with NS in people (including "nephrotic-range" serum albumin concentration and urine protein concentration, and particular glomerular disease subtypes) have been assumed previously to also be important in dogs, although descriptions were limited to those patients included in case series of glomerular disease, and sporadic case reports. However, case-control comparison of larger cohorts of dogs with nephrotic versus nonnephrotic glomerular disease more recently suggests that predisposing factors and concurrent clinicopathologic abnormalities differ from those typically encountered in people with nephrotic syndrome, although case progression and negative effect on patient outcome are similar. This article briefly reviews major current theories and supporting evidence on the pathogenesis of NS, followed by an overview on the clinical features of this syndrome in dogs with glomerular disease. The authors also offer evidence-based and experience-based treatment recommendations that are based on minimizing the suspected dysregulation of the renin-angiotensin-aldosterone axis in affected dogs.