JPC SYSTEMIC PATHOLOGY
SPECIAL SENSES SYSTEM
Signalment (AFIP #1744913): Breed and gender not specified, 17-year-old cat
HISTORY: This cat had bilateral retinal hemorrhage and systemic hypertension.
HISTOPATHOLOGIC DESCRIPTION: Eye: The retina is diffusely thinned with loss of the photoreceptor layer; pseudocyst formation (up to 1X0.5mm) in the photoreceptor layer; 75% reduction of the inner nuclear layer; loss of ganglion cells; vacuolation of the nerve fiber layer or plexiform layer (spongiosis or axonal degeneration). Focally, the retinal architecture is completely obscured by hemorrhage and fibrin admixed with low numbers of fibroblasts and scattered macrophages containing phagocytized erythrocytes and golden-brown granular pigment (hemosiderin). Multifocally, the tunica media of vessels in the retina and choroid is moderately thickened and variably expanded by brightly eosinophilic, hyalinized homogenous material (hyalinization). Occasionally smaller retinal and choroidal vessels are surrounded by increased clear space (edema), and there is choroidal sclerosis and loss of the retinal pigment epithelium. There is multifocal hypertrophy of the retina pigment epithelium (retinal detachment). The heavily pigmented epithelium of the posterior iris forms several knob-like projections that frequently have a clear center (pigmented iridal cysts).
MORPHOLOGIC DIAGNOSIS: Eye, retina: Degeneration, diffuse, marked with detachment, choroidal and retinal vascular hyalinization, focal hemorrhage, and photoreceptor layer pseudocysts, breed unspecified, feline.
CONDITION: Hypertensive retinopathy
- Hypertensive retinopathy, secondary to systemic hypertension, is an increasingly frequent cause of retinal and choroidal lesions and blindness in cats over 10 years of age; 80-100% of cats with systemic hypertension have concurrent retinopathy
- Most cases are associated with chronic renal failure; less common causes include hyperthyroidism, cardiac abnormalities, diabetes mellitus, chronic anemia, high-salt diets, pheochromocytoma, hyperadrenocorticism, acromegaly, primary hyperaldosteronism, and polycythemia
- Dogs and cats are most frequently affected
- The eye is frequently the first organ to clinically manifest systemic hypertension
- Hypertension in cats is commonly defined as systolic pressure greater than 160 -170 mmHg; cats with hypertensive retinopathy often have systolic blood pressures at or above 200 mmHg
- Diseased nephrons > decreased GFR > increased renin (produced by JGA cells) > converts angiotensinogen (in liver) > angiotensin I > increased angiotensin II via ACE (from macula densa of DCT) > arteriolar vasoconstriction increasing peripheral resistance, increased sodium reabsorption, and release of aldosterone from the adrenal cortex, and increased ADH release > distal nephron sodium retention > volume excess and systemic hypertension
- Ocular lesions are the result of sustained & exaggerated autoregulatory vasoconstriction > tunica media hypertrophy > diminished contractile function > fibrous changes > leakage of plasma into arteriolar wall > hyalinization and leiomyocyte necrosis > degeneration > rupture of endothelial & muscle cells > leakage of blood & serum into surrounding retinal tissue > effusive lesions (edema, hemorrhage, retinal detachment)
TYPICAL CLINICAL FINDINGS:
- Lesions are bilateral but not necessarily symmetric
- Acute blindness is the most common reason for presentation
- Hyphema and secondary glaucoma
- Retinal vascular tortuosity
- Retinal detachment
- Intravitreal and intra- and subretinal hemorrhages
- Sustained high blood pressure
- In cats with renal dysfunction, the presence or magnitude of hypertension is unrelated to azotemia; persistent lack of urine concentrating ability may be the only indication of chronic renal disease
- Chronic hypertension causes left ventricular hypertrophy, which is often misdiagnosed as hypertrophic cardiomyopathy
TYPICAL GROSS FINDINGS:
- Intravitreal and intra- and subretinal hemorrhages
- Retinal edema
- Retinal detachment
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Lesions are primarily in the retinal and choroidal vessels; characteristic lesions in the small retinal muscular arteries and larger arterioles
- Mural edema that may progress to a fibrinoid necrosis of the tunica media or medial hypertrophy with adventitial fibrosis of choroid and retinal vessels
- Early lesions, likely to be seen only under experimental conditions, are the result of exaggerated autoregulatory vasoconstriction in response to systemic hypertension
- Changes secondary to vessel damage:
- Localized retinal necrosis
- Exudative retinal detachment and retinal pigment epithelium (RPE) hypertrophy (tombstoning)
- Photoreceptor atrophy and loss
- Retinal hemorrhage, edema, and hemosiderin deposition
- Ischemic necrosis of RPE > allows for leakage of hypertensive edema fluid from the choroid into the subretinal space
ADDITIONAL DIAGNOSTIC TESTS:
- Various clinical diagnostic tests: Ophthalmoscopy, systolic arterial blood pressure, clinical pathology, echocardiography, ocular ultrasound
Retinal disease in cats:
- Taurine deficiency retinopathy (feline central retinal degeneration): Bilateral photoreceptor degeneration; initially affects cone outer segments but also eventually affects rods
- Inherited retinopathies: Autosomal dominant early-onset rod and cone dysplasia with blindness by a few months of age and autosomal recessive late-onset retinal degeneration with blindness by 5-10 years of age; high incidence in Abyssinians
- Secondary retinal degeneration and detachment due to trauma, glaucoma, or infection
- Dogs: At least 60% of dogs with chronic renal failure have systemic hypertension; ocular lesions associated with systemic hypertension are similar to the cat; retinal hemorrhage is the most common hypertension-associated ocular lesion (40%)
- Rats: Spontaneously Hypertensive Rats (SHR) are used as human models
- Non-human primates:
- Diabetic macaques are used as human models for diabetic retinopathy/microvascular disease;
- Hypertension due to catecholamines from pheochromocytomas resulting in myocardial fibrosis as well as hyalinization and medial thickening of coronary arteries recently reported in New World primates (cotton-top tamarin, golden lion tamarin, black howler monkey and black-handed spider monkey); swollen axons (“cotton-wool spots”) are a hallmark of hypertensive retinopathies in primates and may be seen early in the course of disease
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