A 2.5-year-old 12-kg (26.4-lb) castrated male Miniature American Shepherd was referred to the Dermatology Service at The Ohio State University Veterinary Medical Center because of a 3-week history of having a localized, crusted skin lesion on the digital pad of digit 3 of the right hind limb. The lesion had not responded to previous treatment (ie, topical administration of an antimicrobial-anti-inflammatory ointmenta and oral administration of cephalexinb and fluconazolec) prescribed by the referring veterinarian, and the dog had repeatedly chewed on the paw. Radiographs of the digit obtained prior to referral were unremarkable, and serum biochemical analyses performed 8 months earlier had revealed hypercholesterolemia (serum cholesterol concentration, 500 mg/dL; reference range, 80 to 315 mg/dL). Serum triglyceride concentration had not been measured.
On initial dermatologic examination, the digital pad of digit 3 of the right hind limb had, adjacent to the toenail, an approximately 1-cm-diameter, eroded-to-ulcerated lesion with crusted margins. On the same paw, the digital pad of digit 4 had a 0.4-cm-diameter area that was slightly indented and hyperpigmented (Figure 1). Cytologic evaluation of impression smears collected from the crusted area of the third digital pad revealed neutrophils, few cocci, and yeasts. The skin lesion was treated topically with wipes containing chlorhexidine and climbazole,d and a biopsy was recommended.
Photograph of the plantar aspect of the right hind paw of a 2.5-year-old Miniature American Shepherd evaluated because of a 3-week history of a localized, crusted lesion on the pad of digit 3 of the right hind limb on which the dog repeatedly chewed. Note the eroded-to-ulcerated lesion with hemorrhagic crust and partial detachment of the third digital pad and a small indented area with light-brown discoloration on the fourth digital pad.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.209
The owners elected to amputate digit 3 of the affected paw. Histologic evaluation of the digit revealed chronic necrosuppurative inflammation. After surgery, the dog removed the bandage, which was replaced at an emergency clinic close to the owner's house, and the foot later became devitalized. Necrosis, presumably from insufficient tissue perfusion, ascended the limb, necessitating its amputation.
Several weeks after right hind limb amputation, the dog was returned for a second dermatologic evaluation because eroded-to-ulcerated, crusted skin lesions had developed on the plantar surface of the dog's remaining hind limb. In addition, the owner reported that the limb's paw felt cool. Therefore, duplex Doppler ultrasonography was performed to evaluate blood flow within the aorta and major distributing arteries. Ultrasonography revealed intimal thickening of the terminal portion of the aorta and the left external iliac, left and right common carotid, and right brachial arteries (Figure 2), suggestive of atherosclerosis. Echocardiography was performed, and results were unremarkable. Because atherosclerosis was suspected to be the cause of the ischemic lesions, serum biochemical analyses were conducted. Results revealed a baseline cholesterol concentration of 2,364 mg/dL (reference range, 80 to 315 mg/dL), triglyceride concentration of 2,112 mg/dL (reference range, 25 to 75 mg/dL), and total thyroxine concentration of 1.0 μg/dL (reference range, 0.5 to 2.0 μg/dL). Because the dog had developed skin lesions on its remaining hind limb, skin tissue from the previously amputated digit was reevaluated histologically, which revealed severe myointimal atherosclerosis of a deep-dermal, small-caliber artery proximal to the necrotic skin lesion. The marked hyperlipidemia paired with the histopathologic findings was consistent with ischemic necrosis secondary to atherosclerotic plaques. Medical management for hyperlipidemia was initiated with atorvastatin calciume (0.83 mg/kg [0.38 mg/lb], PO, q 24 h), clopidogrelf (1.56 and 3.12 mg/kg [0.71 and 1.42 mg/lb], PO, alternating dose q 48 h), and a fish oil supplement.8 Gabapentinh (8.33 mg/kg [3.79 mg/lb], PO, q 12 h), prescribed at the recheck examination after limb amputation for pain management, was continued, and the dog's diet was changed to a low-fat diet.i
Duplex Doppler ultrasonographic images of the same dog as Figure 1. The aorta (A) and left external iliac artery (B) have broad-based, echogenic material along the luminal surface causing narrowing of the luminal diameter. Turbulent blood flow in the aorta (C) was a result of the change in luminal diameter.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.209
During this second dermatology appointment, the dog was also evaluated because of compulsive licking, generalized anxiety, and fear-related aggression that had first been noticed when the skin lesions developed. It was unclear whether the behavioral changes were related to atherosclerosis of the CNS, an adverse drug reaction, or another problem. Medical management for the behavioral issues included clomipramine hydrochloridej (3.33 mg/kg [1.51 mg/lb], PO, q 12 h) for 2 weeks and trazodone hydrochloridek (2.08 mg/kg [0.95 mg/lb], PO, q 12 h). The gabapentin also contributed to the medical management of the dog's behavior
Three weeks after treatment with atorvastatin calcium, clopidogrel, a low-fat diet, and fish oil was initiated, the patient was reevaluated. On examination, the skin lesions had worsened, and new lesions had developed on the left hind limb, including a hemorrhagic nail, a focal area of indentation on the metatarsal pad, and erythema and crusty lesions near the tibiotarsal joint. The dog appeared more comfortable despite the progression of its skin lesions; therefore, administration of gabapentin was discontinued. Serum biochemical analyses and a CBC performed after food was withheld for 12 hours revealed mild anemia (hemoglobin concentration, 11.6 g/dL [reference range, 12.1 to 18.8 g/dL]; RBC count, 4.7 × 1012 RBCs/L [reference range, 4.8 × 1012 to 8.1 × 1012 RBCs/L]), lymphopenia (0.4 × 109 lymphocytes/L; reference range, 1.0 × 109 to 4.6 × 109 lymphocytes/L), worsening and very severe hypercholesterolemia (serum cholesterol concentration, 4,154 mg/dL), and persistent hypertriglyceridemia (serum triglyceride concentration, 2,047 mg/dL). On the basis of these results and the physical examination findings, the dosage for atorvastatin calcium was increased to 1.66 mg/kg (0.75 mg/lb), PO, every 24 hours; the clopidogrel dosage was kept the same; the fish oil supplement was discontinued; and, in an attempt to improve Theological properties of the blood and increase blood flow to the affected digits, treatment with pentoxifylline1 (16.6 mg/kg [7.55 mg/lb], PO, q 8 h) was initiated.
Seven weeks after medical management was initiated, the owners reported that the dog was reluctant to walk and seemed to show signs of pain and depression. The dog was reexamined, and lesions were noted on the right front foot. All of the toenails were found to be hemorrhagic at the base, the third digital pad was necrotic, and the fourth digital pad was sloughing (Figure 3). An ulcerative lesion was also noted on the metatarsal area of the left hind limb. Administration of gabapentin (8.33 mg/kg, PO, q 12 h) was restarted, a 1% silver oxide ointment1,11 was prescribed for application on affected areas twice daily, and all other medical treatment was continued unchanged. It was also recommended that the owners apply warm compresses to the dog's feet and massage them a few times each day to support blood flow. Unfortunately, the dog's quality of life declined dramatically, and 2 weeks later, the owners elected euthanasia.
Photograph of the right front paw of the dog in Figures 1 and 2 that was obtained 7 weeks later. Hemorrhagic nails, a necrotic digital pad on digit 3, and a sloughing digital pad on digit 4 can be seen.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.209
On necropsy, notable gross findings included changes in the walls of the terminal portion of the aorta and the external and internal iliac arteries. These vessels had raised plaques of irregular, tan-to-yellow, firm, gritty material in their walls (Figure 4). Similar material was identified in the coronary arteries, which were prominent along the epicardial surface and within the myocardium. The thyroid glands appeared grossly normal.
Photographs of the heart and aorta of the dog in the previous figures. Firm yellow plaques are apparent in the coronary arteries and along the length of the aorta (A), particularly in the caudal abdominal segment and internal iliac arteries. Similar firm yellow plaques can also be seen in the lumen of the caudal abdominal segment of the aorta (B).
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.209
A full set of tissue samples was collected and submitted in neutral-buffered 10% formalin for histologic evaluation. In addition to H&E stain, Masson trichrome and elastin stains were applied to tissue sections with diseased vasculature. To identify myofibroblasts, indirect immunohistochemical staining for α-SMA was performed. Specifically, a 5-μm-thick, paraffin-embedded section of tissue with diseased vasculature was pretreated for 30 minutes with a decloaker solution and a commercially available solution for heat-induced target retrieval. The specimen was then incubated for 40 minutes with the primary antibody, a mouse monoclonal IgG antibody (1:100 dilution) against human SMA that also cross-reacts with canine tissue.11 This was followed by application of the secondary antibody, a biotinylated horse anti-mouse IgG antibody (1:200 dilution), and incubation for 30 minutes. Lastly, the slide was incubated with diaminobenzidine chromagen for 5 minutes. To identify lipids, previously unprocessed tissues were stained with oil red O stain.
Mild to severe stenosis of the arterial lumina, with increasing severity as arterial caliber decreased, was observed in the aorta, external and internal iliac arteries, brachycephalic trunk, coronary arteries, renal arteries, and small arteries and arterioles of the heart, spleen, tongue, and brain. The subintimal zones of these vessels were markedly expanded by poorly organized layers of SMA-positive fibroblasts (myofibroblasts) distributed in a collagenous matrix (Figure 5). These layers were interrupted by aggregates of oil red O-positive, lipid-laden macrophages (foam cells) and clear, oil red O-positive, acicular zones (cholesterol clefts). Elastin staining confirmed these features were predominantly on the luminal side of the internal elastic membrane, consistent with fibrointimal hyperplasia. Similar, less severe changes were occasionally seen in the muscular tunics of various arterial segments. These histopathologic findings warranted a diagnosis of marked multifocal segmental intimal and mural atherosclerosis.
Photomicrographs of sections of the abdominal aorta from the dog in the previous figures. A—The subintima is markedly expanded by fibrous connective tissue, lipid (asterisk), and lipid-laden macrophages (foam cells), resulting in severe reduction of the lumen diameter (cross). H&E stain; bar = 100 μm. B— Marked fibrointimal hyperplasia luminal to the internal elastic lamina (asterisk) can be seen. Elastin stain; bar = 100 μm. C—Fibrointimal hyperplasia (asterisk) is evident. Masson trichrome stain; bar = 100 μm. D—Marked expansion of the subintima from the medial tunic (asterisk) can be seen. Immunohistochemical stain for SMA; bar = 100 μm. E—Accumulations of clear acicular material (cholesterol clefts) can be seen. H&E stain; bar = 100 μm.
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.209
All sections of the brain examined (frontal cortex, temporal lobe cortex, thalamus including hippocampus, and cerebellum including brainstem) were characterized by mild widespread degenerative changes, including neuronal satellitosis and mild central chromatolysis, in the cortex as well as edema and vascular congestion in the meninges. The white matter tracts of the brainstem were characterized by moderate to severe axon degeneration with axon sheath swelling and occasional axonal swelling. Atherosclerotic lesions were limited to an atheroma in a temporal lobe section.
Results of a lipid profile performed on a sample of the dog's serum saved at the time of amputation surgery revealed serum LDL concentration of 1,128 mg/dL (reference range, 5.8 to 120.27 mg/dL), cholesterol concentration of 1,409 mg/dL (reference range, 131 to 345 mg/dL), triglyceride concentration of 950 mg/dL (reference range, 20 to 150 mg/dL), and high-density lipoproteins concentration of 91 mg/dL (reference range, 97 to 173 mg/dL).
Discussion
Hypercholesterolemia of the magnitude seen in the present report is rare in veterinary patients, and information regarding the clinical effects of atherosclerosis in dogs is limited.1 Additionally, hypercholesterolemia is often secondary to another condition (eg, diabetes mellitus, hypothyroidism, or hyperadrenocorticism)2; however, none of these predisposing conditions were identified in this patient, clinically or on postmortem examination. For these reasons, hypercholesterolemia was not initially considered as a differential diagnosis for the cause of the skin lesions in this dog. But once severe hypercholesterolemia and hypertriglyceridemia were identified, it became evident that the skin lesions and behavioral problems were likely related to the high blood lipid concentrations.
Development of skin lesions on the remaining hind limb provided indirect evidence for devitalization of the right hind limb after a bandage was applied following digit amputation. The bandage likely further compromised tissue perfusion, resulting in tissue ischemia, necrosis, and, eventually, the need for limb amputation. In addition, atherosclerotic changes were evident by use of ultrasonography. Further, results of histologic examination of the dog's brain were consistent with vascular-mediated disease, providing a reasonable pathological explanation for the dog's behavioral changes and its poor response to medical treatment for those changes.
In dogs, atherosclerosis has primarily been identified in the tunica media and adventitia with occasional extension to the tunica intima3; however, in the dog described in the present report, lipid deposition in all vessels that were examined was intimal with occlusion of the vascular lumen, which is more typical of atherosclerosis in humans.
Primary or familial canine dyslipidemia has been most often observed in Miniature Schnauzers, as first reported by Rogers et al,4 and some unique aspects of lipid metabolism in dogs have been summarized in a review by Xenoulis and Steiner.5 Primary hyperlipidemia has also been reported in Briards, Rough Collies, Shetland Sheepdogs, Doberman Pinschers, Rottweilers, and Beagles, and these dyslipidemias have been characterized by hypercholesterolemia, high serum triglyceride concentrations, or both.5
The condition seen in the dog described in the present report most closely resembled FH seen in children, because the dog was young, had long-standing and severe hypercholesterolemia, and had extensive atherosclerotic lesions more typical of those seen in people than dogs. The key difference between this dog's condition and that of children with FH was the dog's additional and profound increase in serum triglyceride concentration.
In children, FH is an inherited, autosomal-codominant condition characterized by high serum LDL concentrations and deposition of cholesterol in tissues, leading to atherosclerosis.4 The condition is caused by a loss-of-function mutation in the LDLR gene responsible for hepatic uptake and degradation of LDLs or by a mutation in the gene for apoprotein B.6–9 Defects in the LDLR result in loss of feedback mechanisms that control serum cholesterol concentrations.10–12 Children with homozygous FH often present with cutaneous xanthomata, prompting further investigation for hypercholesterolemia.9 The skin lesions in the dog described in the present report were the initial complaint but were determined to be secondary to severe, advanced, vascular lesions. To the authors' knowledge, mutations of the LDLR gene in veterinary patients have not been reported, but might have been a potential cause of the dyslipidemia in this dog.
Human patients with FH are often managed medically with high dosages of statins.13 Similarly, in the dog described in the present report, treatment was initiated with atorvastatin calcium because of the authors' clinical experience14,15 using it, along with a low-fat diet and omega-3 fatty acids. Although atorvastatin calcium may lower serum triglyceride concentration in human patients with moderate to severe hypertriglyceridemia, the authors were not aware of definite evidence for the drug's efficacy in dogs. The plan was to consider initiating treatment with gemfibrozil after the first recheck examination; however, this was not done because of concerns for a possible high risk of adverse effects. Dosages often effective for lowering serum cholesterol and triglyceride concentrations in humans were ineffective in this dog. Although more aggressive treatments (eg, LDL apheresis or liver transplantation3) may often be necessary to address hypercholesterolemia in people, LDL apheresis was not available to the veterinary practices where this dog was treated. Plasmapheresis with a fresh-frozen plasma transfusion was offered; however, the owners declined. Regardless, long-term prognosis for this dog was poor because substantial disease had already developed. For treatment to have been successful, aggressive treatment would have to have been initiated early, prior to plaque formation.
In summary, the young dog of this report had clinical signs related to dyslipidemia and clinical findings similar to those in humans with FH. The dog had severe hypercholesterolemia, hypertriglyceridemia, and diffuse atherosclerosis and atheroma formation. An important feature of this case was that initial clinical signs focused on the skin of the distal aspect of the hind limb; however, signs of ischemic necrosis became more widespread, involving all limbs and affecting behavior despite medical treatment.
Acknowledgments
The authors thank Dr. Catherine Langston for her input on the case.
ABBREVIATIONS
| FH | Familial hypercholesterolemia |
| LDL | Low-density lipoprotein |
| LDLR | Low-density lipoprotein receptor |
| SMA | Smooth muscle actin |
Footnotes
Derma-Vet ointment, Med-Pharmex Inc, Pomona, Calif.
Cephalexin, Teva Pharmaceuticals USA, North Wales, Pa.
Diflucan, Pfizer Inc, New York, NY.
Douxo chlorhexidine 3% PS pads, Ceva Animal Health LLC. Lenexa, Kan.
Lipitor, Pfizer Inc, New York, NY
Plavix, Bristol-Myers Squibb/Sanofi Pharmaceuticals Partnership, Bridgewater, NJ.
Free Form Snip Tips for Small Dogs and Cats, Bayer Animal Health LLC, Shawnee Mission, Kan.
Neurontin, Pfizer Inc, New York, NY
Hill's Prescription Diet i/d Low Fat Canine, Hill's Pet Nutrition Inc, Topeka, Kan.
Clomicalm, Elanco Animal Health, Greenfield, Ind.
Trazodone hydrochloride tablets USP, Qualitest Pharmaceuticals, Huntsville, Ala.
Trantal, Sanofi-Aventis US LLC, Bridgewater, NJ.
Collasate Silver ointment, PRN Pharmacal Inc, Pensacola. F1a.
Mouse clone 1A4, code M0851 (1:100 dilution), Agilent Technologies Inc, Santa Clara, Calif.
References
1 Sato K, Agoh H, Kaneshige T, et al. Hypercholesterolemia in Shetland Sheepdogs. J Vet Med Sci 2000;62:1297–1301.
2 Xenoulis PG, Cammarata PJ, Walzem RL, et al. Novel lipoprotein density profiling in healthy dogs of various breeds, healthy Miniature Schnauzers, and Miniature Schnauzers with hyperlipidemia. BMC Vet Res 2013;9:47.
3 Robinson WF, Robinson NA. Cardiovascular system. In: Maxie MG, ed. Jubb, Kennedy and Palmer's pathology of domestic animals. 6th ed. St Louis: Elsevier, 2015:57–59.
4 Rogers WA, Donovan EF, Kociba GJ. Lipids and lipoproteins in normal dogs and in dogs with secondary hyperlipoproteinemia. J Am Vet Med Assoc 1975;166:1092–1100.
5 Xenoulis PG, Steiner JM. Canine hyperlipidemia. J Small Anim Pract 2015;56:595–605.
6 Goldberg AC, Hopkins PN, Toth PP, et al. Familial hypercholesterolemia: screening, diagnosis and management of pediatric and adult patients: clinical guidance from the National Lipid Association Expert Panel on Familial Hypercholesterolemia. J Clin Lipidol 2011;5(suppl 3):S1–S8.
7 Huang CH, Chiu PC, Liu HC, et al. Clinical observations and treatment of pediatric homozygous familial hypercholesterolemia due to a low-density lipoprotein receptor defect. J Clin Lipidol 2015;9:234–240.
8 Bilheimer DW, Goldstein JL, Grundy SM, et al. Liver transplantation to provide low-density-lipoprotein receptors and lower plasma cholesterol in a child with homozygous familial hypercholesterolemia. N Engl J Med 1984;311:1658–1664.
9 Vuorio A, Docherty KF, Humphries SE, et al. Statin treatment of children with familial hypercholesterolemia—trying to balance incomplete evidence of long-term safety and clinical accountability: are we approaching a consensus? Atherosclerosis 2013;226:315–320.
10 Pang J, Martin AC, Mori TA, et al. Prevalence of familial hypercholesterolemia in adolescents: potential value of universal screening? J Pediatr 2016;170:315–316.
11 Soutar AK, Naomova RP. Mechanisms of disease: genetic causes of familial hypercholesterolemia. Nat Clin Pract Cardiovasc Med 2007;4:214–225.
12 Najam O, Ray KK. Familial hypercholesterolemia: a review of the natural history, diagnosis, and management. Cardiol Ther 2015;4:25–38.
13 Harada-Shiba M, Arai H, Oikawa S, et al. Guidelines for the management of familial hypercholesterolemia. J Atheroscler Thromb 2012;19:1043–1060.
14 Cunningham SM, Rush JE, Freeman LM. Short-term effects of atorvastatin in normal dogs and dogs with congestive heart failure due to myxomatous mitral valve disease. J Vet Intern Med 2013;27:985–989.
15 Herron CE, Brueckner CC, Chism JP, et al. Toxicokinetics and toxicity of atorvastatin in dogs. Toxicol Appl Pharmacol 2015;289:117–123.
