History

A 6-year-old sexually intact male Shetland Sheepdog was evaluated by the primary care veterinarian and subsequently referred to the Matthew J. Ryan Veterinary Hospital at the University of Pennsylvania because of persistent diarrhea, vomiting, and weight loss of 5 weeks' duration.

Clinical Findings

Physical examination by the referring veterinarian revealed tacky mucous membranes and dehydration. Weight loss of approximately 5 kg (11 lb) was reported by the owners, representing approximately 20% of the dog's original body weight. At this time, the dog weighed 19.8 kg (43.5 lb) and had a 5/9 body condition score after the weight loss. Initial clinicopathologic data were obtained by the referring veterinarian (Table 1). Given the isosthenuria and high urine protein-to-creatinine concentration ratio, the azotemia was considered to be of renal origin. Enalapril administration was started (0.57 mg/kg [0.26 mg/lb], PO, q 24 h) to mitigate the proteinuria. To maintain hydration, lactated Ringer solution with supplemental potassium was administered IV at a rate of 5.7 mL/kg/h (2.59 mL/lb/h).

Ten days later, after unsuccessful supportive treatment and overhydration, the dog was referred to the veterinary teaching hospital. At this time, the dog weighed 21.9 kg (48.2 lb). The dog was also thrombocytopenic. Serum biochemical analysis and urinalysis were repeated (Table 1), and treatment was altered. Enalapril was replaced with benazepril (1.15 mg/kg [0.5 mg/lb], PO, q 24 h). To avoid further overhydration, fluid therapy was changed to a combination of hetastarch (0.5 to 1 mL/kg/h [0.23 to 0.45 mL/lb/h]) and an isotonic crystalloid solution (1.15 to 1.43 mL/kg/h [0.52 to 0.65 mL/lb/h]); an antacid, esomeprazole sodium (0.5 mg/kg, IV, q 12 h), and an antiemetic, dolasetron mesylate (0.7 mg/kg [0.32 mg/lb], IV, q 24 h), were administered for gastrointestinal tract protection.

Three days after admission to the veterinary teaching hospital, thromboelastography was performed and revealed a low κ value (representative of the rate of clot formation) in conjunction with high angle and maximum amplitude (MA) value, all of which suggested a state of hypercoagulability (Table 1). Dalteparin sodium (100 U/kg [45.45 U/lb], SC, q 12 h) was administered prophylactically. Abdominal ultrasonography revealed minimal peritoneal effusion, bilateral irregularly shaped renal cortical architecture with decreased corticomedullary distinction, and a possible blood clot in the urinary bladder. Taken together, the clinical data indicated severe proteinuria, mild renal azotemia that partially improved with fluid therapy, and hypercholesterolemia. An ultrasound-guided needle biopsy specimen of the left kidney was submitted to the Texas Veterinary Renal Pathology Service for light microscopic, transmission electron microscopic (TEM), and immunofluorescence evaluations.

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Microscopic and Immunofluorescence Findings

Sections of the renal biopsy specimen were routinely stained with H&E, periodic acid–Schiff, Masson trichrome, Congo red, and toluidine blue stains. The renal sections contained portions of 16 glomeruli for evaluation, and the predominant lesion was segmental effacement of capillary lumens by the extracellular matrix (focal segmental glomerulosclerosis). Adhesions between the tuft and Bowman capsule (synechiae) were common. Acicular clear spaces (cholesterol clefts) were found within glomerular capillary lumens (Figure 1). Small accumulations of clear crystalline material (mineral) admixed with lipid (which had dissolved during processing) were present in the walls of interlobular arteries. In 1 artery, this material was located immediately below the tunica intima. Tubules were in variable stages of degeneration often accompanied by attenuation of the remaining epithelial cells. Portions of 4 glomeruli were selected for oil red O staining and evaluation. All glomeruli contained an abundance of small to large red globules (indicative of lipid).

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Photomicrographs (obtained by light and transmission electron microscopy) of sections of a renal biopsy specimen from a Shetland Sheepdog that was initially evaluated because of persistent diarrhea, vomiting, and weight loss of 5 weeks' duration and was subsequently found to have azotemia, proteinuria, and hypercholesterolemia. A—In a section of a glomerulus, notice the acicular clear spaces (cholesterol clefts) in a glomerular capillary lumen. H&E stain; bar = 50 μm. B—In a serial section of the glomerulus in panel A, the cholesterol clefts in the glomerular capillary lumen are visible, which is diagnostic for atheroembolic disease in humans. Periodic acid–Schiff stain; bar = 50 μm. C—In an interlobular artery, there is crystalline material admixed with lipid (the latter of which dissolved during processing) in the tunica media immediately below the tunica intima. Periodic acid–Schiff stain; bar = 75 μm. D—In a section of a glomerulus from a biopsy core of fresh renal tissue, notice the presence of abundant lipid within the tuft. Oil red O stain; bar = 50 μm. E—Similar atheroemboli are visible in a 1-μm-thick section of a glomerulus. Toluidine blue stain; bar = 50 μm. F—In a TEM image of a section of the glomerulus depicted in panel E, notice the presence of linear cholesterol clefts as well as osmophilic lipid globules (arrow). Uranyl acetate–lead citrate stain; bar = 2 μm.

Citation: Journal of the American Veterinary Medical Association 250, 5; 10.2460/javma.250.5.515

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One glomerulus was evaluated ultrastructurally by use of TEM (Figure 1). There was mesangial expansion and global podocyte foot process effacement. Both the capillary and mesangial regions contained osmophilic globules. Additionally, acicular clefts were present within a capillary lumen.

Direct immunofluorescence staining of renal biopsy cores was performed with fluorescein isothiocyanate-labeled antibodies against canine IgG,^a IgM,^a IgA,^a and complement component 3 (C3).^a Sections stained with anti–IgG or anti–IgM antibody were negative. Sections stained with antibodies against IgA or C3 did not contain glomeruli; therefore, the presence or absence of these proteins in glomeruli was unknown.

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: focal segmental glomerulosclerosis with glomerular atheroemboli and subacute to chronic tubular degeneration and atrophy.

Case summary: glomerular atherosclerotic emboli in a dog.

Comments

Although the dog of the present report originally was examined because of enteric signs, detection of proteinuria and azotemia led to identification of atheroemboli in glomeruli. The presence of cholesterol clefts in glomerular capillaries is diagnostic for atheroembolic disease in humans. The source of cholesterol emboli in humans is most commonly atherosclerotic plaques.¹ Aortic surgery and angiography are known to disrupt atherosclerotic plaques and increase the risk of release of cholesterol emboli.^1–4 A retrospective study that analyzed clinical and pathological reports found that at the time of diagnosis, 75 of 221 humans with cholesterol crystal embolization had a prior history of or had developed renal failure. Furthermore, the kidney was the most common organ for postmortem identification of cholesterol crystal emboli.⁵ In humans, the mainstay of treatment for atheroemboli is hemodialysis while the kidney recovers from the associated ischemic injury. The dog of the present report received traditional supportive care but was not treated with hemodialysis. The owners elected for euthanasia 3 days after the kidney biopsy specimen was obtained owing to the dog's lack of clinical improvement.

Although glomerular atherosclerotic embolism of renal vasculature is a well-defined entity in humans, it has not been previously described in dogs, to our knowledge. In fact, there are only a few reports that describe any type of lipid deposition within canine kidneys and none describe cholesterol clefts in glomeruli. Studies performed by Zayed et al⁶ and Thiel et al⁷ both used light microscopy and TEM to detect glomerular lipidosis in dogs. The TEM findings in both studies indicated that the lipid stores were primarily located in mesangial cells, at which point the cells were described as foam cells. Neither of those studies included clinical observations (eg, renal failure or urinalysis results) that coincided with the TEM findings. In contrast, a report of a diabetic dog after partial cystectomy described globular lipid emboli within the glomerular capillary lumens, nodular glomerulosclerosis, and thickened glomerular capillary basement membranes.⁸

The dog of the present report had mesangial lipidosis, globular lipid emboli (identified by TEM), and atheroemboli, suggesting a possible link among the glomerular lesions. Interstitial arteries had crystalline and lipid material under the tunica intima; however, a postmortem examination was not performed on this dog so the presence or absence of systemic atherosclerotic plaques could not be determined. Atherosclerosis in dogs has been associated with hypothyroidism and diabetes mellitus.^9,10 Shetland Sheepdogs are predisposed to hypothyroidism,¹¹ but this dog had neither hypothyroidism nor diabetes mellitus. However, the dog did have hypercholesterolemia, which could have promoted development of atherosclerosis.

Focal segmental glomerulosclerosis was the cause of the dog's protein losing nephropathy. A recent study¹² revealed that 103 of 501 (approx 20%) of North American dogs undergoing renal biopsy for the clinical indication of proteinuria had focal segmental glomerulosclerosis without underlying immune complex disease. Protein loss inherent to nephrotic syndrome and subsequent loss of antithrombin III have been historically associated with the induction of a hypercoagulable state in dogs.¹³ More recently, it has been found that variables such as serum albumin concentration and antithrombin activity are unreliable when used as sole predictors of hypercoagulability.¹⁴ Thus, a full coagulation panel and thromboelastography should be performed whenever possible.

In the dog of the present report, the tubulointerstitial disease was subacute to chronic and likely resulted from multiple phenomena. First, the arterial lesions and the presence of atheroemboli can cause ischemia. Second, tubular reabsorption of filtered glomerular proteins leads to pro-inflammatory and profibrotic responses.¹⁵ Advancements in the field of veterinary renal pathology make renal biopsy a tool of great diagnostic and prognostic value in contemporary veterinary practice. Notably in this case, examination of the renal biopsy specimen provided the clinician with important information, namely that the dog had irreversible glomerular and tubulointerstitial damage.