Is it SARDS or CAR?

Sudden acquired retinal degeneration syndrome (SARDS) is a frequent cause of irreversible blindness in dogs. It is thought to be an autoimmune disease like autoimmune retinopathies in humans (AIR). In humans, autoimmune retinopathies can develop as a form of paraneoplastic syndrome or when there is no cancer. Presentations of cancer-associated retinopathy (CAR) and SARDS (nonparaneoplastic clinical entity) in dogs are similar, therefore this investigation describes some elements that could be used to differentiate between the two conditions.

The sample of this study consisted of 17 dogs, diagnosed with SARDS or immune-mediated retinitis (IMR) by eight different ophthalmologists. All were diagnosed with a malignant tumor – 16 before or at the time of the visual problem and one 24h after the blindness. The most frequent tumor was meningioma, followed by sarcoma.

Dogs underwent complete systemic and ophthalmic examination. The histological and molecular changes in retinal tissue were evaluated using microarray and IHC analysis. None of these patients had the classic combination of SARDS responses, i.e., flat electroretinography combined with no red-good blue chromatic pupil light reflex testing, thus they were then diagnosed with IMR (immune-mediated retinitis).

Fundoscopic evaluation revealed various changes like those observed in SARDS eyes, being retinal vascular attenuation the most frequent. Histology was compatible with photoreceptor loss and various systemic changes were described (e.g., proteinuria/microalbuminuria in 77.7% of the patients). Western blotting analysis revealed the presence of serum anti-retinal autoantibodies in 80% of tested canine IMR-CAR patients.

Even though there were almost identical clinical presentations in many cases, SARDS and CAR eyes were clearly different regarding overall gene expression. In patients with CAR, genes mediating immune responses and with functions in apoptosis and inflammation signaling were more prevalent.

Immunosuppressive therapy resulted in the reversal of complete blindness in 44% of treated patients. In fact, this is the first study reporting the usage of intravitreal intravenous immunoglobulin as a safe, cost-effective, and powerful method for treating inflammatory and autoimmune ocular diseases.

Grozdanic, S. D., Lazic, T., Kecova, H., Mohan, K., Adamus, G., & Kuehn, M. H. (2021). Presumed cancer-associated retinopathy (CAR) mimicking Sudden Acquired Retinal Degeneration Syndrome (SARDS) in canines. Veterinary ophthalmology, 24(2), 125–155. https://doi.org/10.1111/vop.12853