Comprehensive Pathologic Evaluation of Kidney Disease in Dogs and Cats: 179 Cases (2005-2007)
Nephropathology in human medicine is a well-established subspecialty in which thorough light microscopic (LM) examinations are routinely combined with transmission electron microscopic (TEM) examinations and immunofluorescence (IF) evaluations to adequately characterize the pathologic features of diseases affecting kidneys. Pathologic findings are integrated with clinical findings to render specific morphologic and disease diagnoses and guide appropriate therapy. We hypothesized that taking a similar approach to the pathologic evaluation of renal diseases in dogs and cats would improve diagnosis and treatment of kidney disorders in these animals.
Early in 2005, we established a diagnostic veterinary renal pathology service that: (a) provides kits of materials and instructions that enable clinicians to properly obtain and submit specimens of kidney suitable for TEM and IF, as well as histologic (LM) examinations, (b) routinely performs thorough LM, TEM, and IF evaluations, and (c) focuses on identifying pathologic implications for clinical patient management (i.e., diagnosis, prognosis, treatment). Our initial experiences in this activity have yielded some noteworthy observations.
Case submissions increased annually (2005, 19; 2006, 51; 2007, 109) and totaled 179 by the end of 2007. Submissions mainly were from dogs (n, 165) and most were biopsies (154 biopsy and 11 necropsy cases). Submissions from cats (n, 14) were too few to summarize in a meaningful way. Glomerular diseases of various types predominated in most (107/165; 64.8%) of the canine cases, and the remaining cases (58/165; 35.2%) were an eclectic mix of other disorders, including juvenile-onset nephropathies, acute or chronic interstitial nephritis, and acute tubular injury. The biopsy specimens varied in quality, but generally were sufficient for diagnosis; only 9/154 (5.8%) were judged to be inadequate. Importantly, biopsy specimens, which typically are obtained at an earlier stage of disease than necropsy specimens, exhibit a much more diverse and informative range of pathologic changes than is evident in necropsy specimens or is well characterized in the veterinary literature. A membranoproliferative pattern of glomerular injury was the single most common histologic lesion observed, but seemingly had multiple causes, including some for which evidence of glomerular immune-complex deposition could not be demonstrated.
We conclude that thorough nephropathologic evaluations, especially of biopsy specimens that are properly obtained from appropriate patients and correlated with relevant clinical information, often provide previously unappreciated insights about the causes and pathogenesis of kidney diseases in dogs and cats. If they are obtained, prepared, and submitted properly for LM, TEM, and IF evaluations, biopsy specimens are especially informative because they offer excellent tissue quality and often exhibit early stages of disease development, when distinctive diagnostic features are more readily apparent and specific, well-targeted therapeutic interventions are more likely to improve clinical outcomes.