Clonal Rearrangements in Feline Borderline Idiopathic Inflammatory Uveitis: Presumed Transformation into Solitary Intraocular Lymphoma

Introduction: Feline intraocular lymphoma is generally considered secondary to systemic lymphoma. Recently, presumed feline solitary intraocular lymphoma (S-IOL) has been reported and intraocular inflammation has been hypothesized to play a role in its emergence. Human primary IOL is a rare but well characterized entity, often referred to as ‘masquerade syndrome’, as it mimics uveitis. Our aim was to investigate cases of feline idiopathic anterior uveitis refractory to therapy that histologically were considered ‘borderline lesions’, possibly consistent with S-IOL. Materials and Methods: Ocular globes from five domestic short hair cats (mean age 8.5 years, M/F ratio 5 1) with an original diagnosis of idiopathic inflammatory uveitis borderline (n54) and feline idiopathic lymphoplasmacytic uveitis (n 5 1) were immunophenotyped using anti-CD3, anti-CD20 and anti-CD79a antibodies. DNA from paraffin wax-embedded tissues was extracted for clonality testing. Results: Clonal TCRG was observed in three borderline cases and in the case of lymphoplasmacytic uveitis. Clonal TCRG and clonal IgH rearrangement was seen in one borderline case. A mixed lymphocytic inflammatory infiltrate was present in all cases as evidenced by IHC (5/5) and polyclonal T cell populations (3/5). Conclusions: Coexistence of a mixed lymphoplasmacytic infiltrate is supportive of the hypothesis that feline S-IOLs are lymphomas emerging within an inflammatory process. T-cell origin prevailed within this small group of S-IOLs. Clonal IgH and TCRG rearrangement may reflect an emerging B-cell lymphoma with a clonal antitumour T-cell response. Alternatively, a lymphoma with cross lineage rearrangement has to be considered. Diagnosis of S-IOL is complex and needs the support of multiple diagnostic tools.