The long‐term outcomes of standing superficial keratectomy as the sole treatment of corneal B‐cell lymphoma in five horses in the UK: Clinical, histopathology, immunohistochemical and molecular findings

Abstract

SummaryThis case report describes five horses with solitary corneal B‐cell lymphoma treated with superficial keratectomy as a sole treatment and their long‐term follow‐up. All five cases had a presumed clinical diagnosis of immune‐mediated keratitis (IMMK) which was initially responsive to immunosuppressive or immunomodulatory treatment. Between 6 and 71 months from the start of clinical disease, these cases became refractory to treatment. All five horses underwent superficial keratectomy under standing sedation and regional anaesthesia. A focal superficial keratectomy was performed in one horse to remove the affected area, and in the remaining four horses, the superficial cornea was removed in its entirety. Histopathology, immunohistochemistry (IHC) and polymerase chain reaction for antigen receptor rearrangements (PARR testing) were performed on all five keratectomy specimens. The histopathological and immunohistochemical findings indicated a florid stromal infiltrate of mitotically active, intermediate to large B‐lymphocytes amidst a variable background of chronic keratitis. In three of the five cases, the lymphocytes displayed prominent epitheliotropism. PARR testing confirmed rearrangements of, specifically, IGH2, IGH3 and KDE, indicating B‐cell clonal expansion consistent with B‐cell lymphoma. There has been no local recurrence in any of the five horses over 24–84 months of follow‐up and no clinical evidence of multicentric lymphoma. No adjunctive treatment was given post‐keratectomy and all eyes have remained comfortable and off treatment. Results of this report show that standing superficial keratectomy is a viable diagnostic tool and a long‐term treatment option for diffuse intermediate to large corneal B‐cell lymphoma.