Immunohistochemical investigation of canine episcleritis

To identify macrophages, B cells and T cells in archived canine episcleral biopsies and to correlate these findings with the clinical presentation and therapeutic outcome.

Archived formalin-fixed biopsies were immunohistochemically labeled for CD18, CD79a, and CD3 to identify macrophages, B cells and T cells, respectively. Slides were digitally photographed and positive cells were manually counted. Signalment, duration of illness, affected eye(s), treatment, and therapeutic outcome were reviewed for each dog. Dogs were divided into groups based on clinical presentation (unilateral episcleritis, bilateral episcleritis or nodular granulomatous episclerokeratitis (NGE).

Twenty-four cases were evaluated. There were 19 episcleritis (13 unilateral, six bilateral) and five NGE cases. The mean age for clinical manifestations of unilateral episcleritis was 6.8 years, bilateral episcleritis was 8.7 years, and NGE was 3.8 years. The Cocker Spaniel was over-represented in the episcleritis groups. All NGE cases were Collies. Approximately 50% of the unilateral episcleritis cases resolved and did not require long-term therapy. Almost all cases of bilateral episcleritis and NGE required continuous medical therapy to maintain remission. There was a significantly higher percentage of B lymphocytes in biopsies from lesions that required ongoing medical therapy to maintain lesion remission than in the lesions that resolved, and for which medications were discontinued (P = 0.0471).

The prognosis for resolution of NGE and bilateral episcleritis without long-term medical therapy is poor. There is a significant difference in the inflammatory cell population in episcleritis that resolved with medical therapy vs. episcleritis that required ongoing medical therapy.