Aug
6
2008

A new eye disease in dogs has been identified, and with it, a potential for a cure. But many veterinary ophthalmologists are not convinced that it is really a new disease.

Sinisa Grozdanic, assistant professor of veterinary medicine at Iowa State University discovered the disease, which he named Immune-Mediated Retinitis (IMR). He published his findings in the March issue of Veterinary Clinics of North America: Small Animal Practice.

According to the report, the discovery of IMR is significant because of its similarity to Sudden Acquired Retinal Degeneration Syndrome (SARDS). In both diseases, the dog’s autoantibodies attack cells in the retina, causing vision impairment or loss.

SUBTLE DIFFERENCES

Grozdanic said he discovered the disease while working on a rapid diagnostic test for SARDS involving shining red and blue lights into the dog’s eye to test pupil light reflex. He said that a subpopulation of the patients he tested responded to the lights in a manner similar to SARDS patients – pupils were responsive to blue light but not red – but there were subtle differences.

“When we started to look more closely in these dogs we noticed that all of them still had some retinal electrical activity detectable by electroretinography (ERG),” he said.

Dogs with SARDS display no ERG readings, but in IMR cases the retinas still show electrical activity, according to the report. Another difference is that in SARDS the autoantibodies originate inside the eye, whereas in IMR, the autoantibodies appear to originate in other parts of the body, Grozdanic said.

According to Grozdanic, about 2,000 cases of SARDS are reported each year, but some of those are probably misdiagnosed and are actually IMR. There is currently no generally accepted cure for SARDS, but Grozdanic said that in some of his SARDS patients, intravenous immunoglobulin treatment restored enough vision for a dog to navigate a maze.

Grozdanic said that he treated many of his IMR patients successfully with high doses of steroids and doxycycline.

“Approximately 50 percent of dogs responded to this therapy,” he said. “In some patients we managed to improve condition by using intravenous immunoglobulins (IVIg), however 40-50 percent of patients do not respond to any form of therapy and we are looking in possible reasons why some of these patients are refractory to treatment.”

Grozdanic said that he has followed some of his patients for two years, and they are “still visual.” Some are still on the steroid therapy, but others are off therapy altogether.

“The most important thing to remember is that both diseases are potentially treatable if diagnosis is established early enough,” he said. “Furthermore, IMR patients frequently respond to relatively cheap medical treatment (steroids and doxycycline), which further enhances the need to properly diagnose these patients.”

SOME DOCTORS SKEPTCIAL

However, not everyone is ready to buy into Grozdanic’s findings.

Chicago veterinary ophthalmologist Paul A. Gerding Jr., DVM, DAVCO, said he is not quite ready to accept that there is a safe and proven cure for SARDS, or that IMR is a distinct disease.

“It’s not something with the current results to date that we have all necessarily agreed is what it’s proposed to be,” Gerding said. “At least right now, I’m not sure with the information that I’ve read that I can come to the conclusion that it exists as a sole disease that can be treated.”

Gerding said he would need to see a longer term results before using Grozdanics treatments but hopes that there will be an effective and safe treatment available soon.

“As a researcher I’m always optimistic, as a practitioner I’m always cautious,” he said.

Kenneth Abrams, DVM, DAVCO, of Veterinary Ophthalmology Services, Inc., in Rhode Island said he set up a conference call with several colleagues to discuss the article. He said they were not convinced that IMR was a credible disease.

“Quite a few of the clinical signs that they present as IMR really could be clinical signs of optic neuritis,” Abrams said. “We all came away with the same comments, that we were awfully skeptical of it.”

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