Third Eyelid T-cell-Rich Large B-cell Lymphoma Positive to EHV-5 in a Mare—a Case Report

Lymphoma is a rare neoplasm in the horse; nevertheless, it is the most frequent hematopoietic neoplasia in this species. It is classified according to the anatomical distribution of the lesion in multicenter, alimentary, mediastinal, cutaneous, and atypical/solitary form. Extraocular lymphoma mainly occurs as secondary lesion in cutaneous or multicentric form, whereas few reports show the presence of primary form of extraocular lymphoma. Ocular adnexa which are reported to be affected by lymphoma include third eyelid, eyelid, and the cornea. To date, no etiological agents are known. In this case report, we describe a case of T-cell-rich large B-cell lymphoma of the third eyelid in a mare never reported in literature, investigated with histology, immunohistochemistry, and flow cytometry. Moreover, for the first time, the presence of equine herpesvirus-5 was identified with a biomolecular analysis on the third eyelid tissue affected by lymphoma.