Sudden acquired retinal degeneration syndrome was first described in 1983,1 and since that time, there has been little discovered to help elucidate the etiology. Sudden acquired retinal degeneration syndrome typically affects middle-aged to older dogs with clinical signs of acute loss of vision bilaterally. Ophthalmic examination reveals dilated pupils at rest and usually a weak pupillary light reflex. Some dogs may have mild to moderate conjunctivitis. There is no intraocular inflammation, and no abnormalities are detected on ophthalmoscopic examination of the fundus. The definitive diagnosis of SARDS is made via electroretinography, which reveals a bilaterally extinguished waveform. The acute pathologic lesions are located in the outer segments with the rod and cone outer segments affected equally. Over several weeks, there is gradual degeneration of all layers of the retina, eventually resulting in the classic ophthalmoscopic signs of retinal degeneration.2,3,a Death of photoreceptors appears to be caused by apoptosis with no evidence of inflammation.4 Many dogs with SARDS have unexplained clinical signs similar to hyperadrenocorticism, such as polydipsia, polyuria, polyphagia, and weight gain, usually just prior to acute vision loss.5,6,b Although for some of those dogs, results of a screening test for hyperadrenocorticism will be positive, when pursued with definitive laboratory tests or adrenal gland and pituitary gland imaging, dogs with SARDS rarely have true hyperadrenocorticism.6,7,c Clinical signs of polyuria, polydipsia, and polyphagia often subside and resolve over several months.
Cancer-associated retinopathy in humans is an immune-mediated disease that causes rapid, bilateral vision loss. The most common tumor associated with CAR is small cell lung carcinoma. Although several retinal antigens have been identified as targets, CAR is most commonly associated with the 23-kd protein, recoverin.8–14 Recoverin is a calcium-binding protein, primarily found in photoreceptors, that inhibits rhodopsin kinase in the phosphorylation of rhodopsin during phototransduction. Cancer patients with CAR have aberrant production of recoverin by tumor cells. Host antibodies directed against the aberrant recoverin gain access to photoreceptors across the bloodretinal barrier and initiate caspase-dependent apoptotic cell death of photoreceptors.15,16 As in dogs with SARDS, humans with CAR do not have intraocular inflammation, and no abnormalities are detected on initial ophthalmoscopic examination of the fundus. Electroretinography reveals a severely attenuated to extinguished waveform bilaterally, localizing the pathologic lesion to the photoreceptors.
To investigate a comparative pathogenesis between CAR and SARDS, the purposes of the study reported here were to evaluate dogs with SARDS for evidence of pituitary gland, adrenal gland, and pulmonary neoplasia and antiretinal antibodies and to evaluate dogs with neoplasia for antiretinal antibodies.
Sudden acquired retinal degeneration syndrome
Pituitary gland height-to-brain area ratio
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Abrams KL, Gareen IF, Marchand KN. Factors associated with canine sudden acquired retinal degeneration syndrome (SARDS)—350 cases (abstr), in Proceedings. 32nd Annu Meet Am Coll Vet Ophthalmol 2001;17
Holt E, Feldman EC, Buyukmihci NC. The prevalence of hyperadrenocorticism (Cushing's Syndrome) in dogs with sudden acquired retinal degeneration (SARD) (abstr), in Proceedings. 30th Annu Meet Am Coll Vet Ophthalmol 1999;35
Aspen, Acuson Corp, Mountain View, Calif
GE Sytec 4000i, General Electric Medical Systems, San Francisco, Calif
Renocal 76, SICOR Pharmaceuticals Inc, Irvine, Calif
NitroBind, Fisher Scientific, Pittsburgh, Pa
Courtesy of Paul Hargrave, University of Florida, Gainsville, Fla
Biotinylated goat anti-dog antibody, Santa Cruz Biotechnology, Santa Cruz, Calif
Biotinylated goat anti-rabbit antibody, Vector Laboratories, Burlingame, Calif
Biotinylated horse anti-mouse antibody, Vector Laboratories, Burlingame, Calif
Streptavidin horseradish peroxidase, Vector Laboratories, Burlingame, Calif
Diaminobenzidine, Sigma-Aldrich, St Louis, Mo
Carter RT, Bentley E, Oliver JW, et al. Elevations in adrenal sex hormones in canine sudden acquired retinal degeneration syndrome (SARDS) (abstr), in Proceedings. 34th Annu Meet Am Coll Vet Ophthalmol 2003;40
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