Hemostatic profiles in dogs with sudden acquired retinal degeneration syndrome

**Background:** Sudden acquired retinal degeneration syndrome (SARDS) is a common cause of irreversible blindness in dogs with an incompletely understood pathogenesis. Dogs with SARDS often exhibit systemic signs resembling hypercortisolism, which is associated with hypercoagulability. The role of hypercoagulability in SARDS is unknown. This study aimed to determine hemostatic profiles in dogs with SARDS.

**Methods:** The study consisted of two parts: a prospective pilot study and a prospective case-control study. In the pilot study, 12 dogs with a history of SARDS underwent thromboelastography (TEG). In the case-control study, 7 dogs with recent onset of SARDS (vision loss <6 weeks) and 7 age-, breed-, and sex-matched healthy controls were enrolled. All dogs underwent complete blood count, serum biochemistry, urinalysis, TEG, fibrinogen concentration, antithrombin activity, D-dimers, thrombin-antithrombin complexes, and optical platelet aggregometry. Hypercoagulability was defined as a TEG G value above the upper limit of the institutional reference interval (>8.9 kdynes/s). Statistical analysis used multiple linear regression with backward selection and Welch's t-test where appropriate.

**Key Results:** In the pilot study, 9/12 dogs with a history of SARDS were hypercoagulable based on increased TEG G value (median 12.7 kdynes/s; range 8.1-18.2; reference interval 4.0-8.9). Of 3 dogs tested, 2 had hyperfibrinogenemia. In the case-control study, all 7 dogs with SARDS and 5/7 controls were hypercoagulable based on TEG G value. Dogs with SARDS had significantly higher G values (median 12.7 kdynes/s; range 11.2-25.4; P = .04) and plasma fibrinogen concentration (median 463 mg/dL; range 391-680; P < .001) compared to controls (median G 10.6 kdynes/s; range 6.4-11.8; median fibrinogen 297 mg/dL; range 166-393). TEG maximum amplitude was also significantly higher in SARDS dogs (median 71.7 mm; range 69.1-83.5) vs. controls (median 68 mm; range 56.2-70.2; P = .02). No significant differences were found in platelet count, hematocrit, antithrombin activity, D-dimers, thrombin-antithrombin complexes, or platelet aggregometry between groups. Strong positive correlations were found between TEG-G and fibrinogen (R² = 0.49; P = .01) and TEG-MA and fibrinogen (R² = 0.43; P = .01).

**Clinical Implications:** Hypercoagulability is common in dogs with SARDS, driven primarily by increased plasma fibrinogen concentration rather than platelet abnormalities. The finding that matched controls also frequently showed hypercoagulability suggests that age and breed may contribute, but SARDS dogs are significantly more hypercoagulable. This hypercoagulable state may contribute to impaired choroidal perfusion, similar to proposed mechanisms in human central serous chorioretinopathy. However, hemostatic tests were not useful as discriminatory biomarkers for SARDS. The role of hypercoagulability in SARDS pathogenesis remains to be determined, and further studies using choroidal vascular imaging are warranted.