Sudden acquired retinal degeneration (disease)

Sudden acquired retinal degeneration syndrome (SARDS) is a disease in dogs causing sudden blindness. It can occur in any breed, but female dogs may be predisposed.^[1] Approximately 4000 cases are seen in the United States annually.^[2]

Characteristics

Symptoms include sudden permanent blindness, but may occur more slowly over several days, weeks or months,^[3] dilated pupils. Pupillary light reflexes are usually reduced but present; the slow phase mediated by melanopsin in retinal ganglion cells is retained. Other symptoms commonly seen are similar to those seen with Cushing's disease and include increased water consumption and urination, weight gain, confusion, restlessness, behavioral changes and lethargy. These symptoms may develop over a few months preceding the onset of SARDS.^[4] Clinical signs and disease progression vary markedly among individual animals, depending on the number and type of hormones that are increased, the degree of hormone elevation, and the age of the dog.^[5]

Some owners notice a more obvious "eye shine" in photographs due to the dilated pupils and retinal atrophy creating what is described as a "hyper-reflective tapetum".

Causes

The cause of SARDS is considered to be idiopathic and the veterinary community is divided as to its cause, but the disease possibly involves autoimmune disease, toxins, elevations in adrenal sex hormones^[5] or Cushing's disease.^[6] Despite similar symptoms and blood test results to Cushing's disease, evaluation of dogs with SARDS did not reveal any tumors in the pituitary or adrenal glands.^[7]

However, endocrine testing (i.e., Canine Adrenal Panel at the University of Tennessee College of Veterinary Medicine Endocrinology Service)^[8] often shows elevations in adrenal sex hormones.

Autoimmune disease as a cause has also been called into question because of a lack of antiretinal autoantibodies in dogs with SARDS in one study.^[9]

Diagnosis

Examination with an ophthalmoscope will initially show no changes, but in a few months atrophy of the retina will resemble the appearance of progressive retinal atrophy. Pathologically, there is a loss of the rod and cone cells followed by degeneration of other layers of the retina. The retinal degeneration appears to be related to apoptosis of these cells.^[10] SARDS must be distinguished from other causes of sudden blindness that have no visible pathology, including retrobulbar optic neuritis, a tumor at the optic chiasm, or other central nervous system diseases. Electroretinography is useful to definitively diagnose SARDS.^[11]

Treatment

Currently there is no approved treatment, although the use of intravenous immunoglobulin has been investigated due to similarities between SARDS and human immune-mediated retinopathy.^[2]

Endocrine testing by National Veterinary Diagnostic Services^[12] (the only laboratory that offers the endocrine-immune blood test developed by Alfred Plechner, DVM)^[13] revealed that some pets with SARDS had endocrine-immune abnormalities^[14][15] and physiological doses of cortisone and thyroid hormone were anecdotally shown to be beneficial to their overall health and vision.^[16][17][18] "Adrenal exhaustion"^[19] is a syndrome put forth by Ms. C. Levin, a lay person, who subscribes to the theories of Dr. Plechner. However, "adrenal exhaustion" (not to be confused with Addison's disease) is not recognized as a legitimate medical disorder in veterinary medicine and the condition has not been described in dogs (or cats). Moreover, this experimental hormone replacement therapy has not been approved or evaluated for efficacy and safety by the veterinary community, nor has it undergone scientific peer review in the mainstream veterinary literature.

Additional information on SARDS may be found at this website http://www.sardsawareness.com which provides links to research carried out by Dr. Sinisa Grozdanic, D.V.M., Ph.D., Associate Professor of Comparative Ophthalmology at the College of Veterinary Medicine at Iowa State University, in Ames, Iowa. The website provides a link to a Powerpoint presentation summarizing the work of Dr. Grozdanic and his co-researchers ^[20] This is another link to a news release describing Dr. Grozdanic's work: http://www.sciencedaily.com/releases/2008/03/080304173310.htm Dr. Grozdanic has found that SARDS like symptoms may be related to a similar disorder which he calls Immune-Mediated Retinopathy, or IMR, which causes loss of function in retinal cells and, in some cases, blindness in canines. In SARDS cases there is permanent damage to retinal cells, but in IMR cases there is loss of function of the retinal cells which may be partially reversed by treatments developed by Dr. Grozdanic, and an affected dog's vision may be restored to a degree where the dog has functioning eyesight again. Not all dogs are candidates for his treatments, which may be contra-indicated by other underlying health disorders.

References