Autoimmune uveitis in a Thoroughbred gelding with common variable immunodeficiency

Common variable immunodeficiency (CVID) is the most common primary immunodeficiency in horses. CVID is classically characterised by persistent hypo‐ or agammaglobulinaemia, progressive B‐cell lymphopenia and lack of response to protein‐based vaccines. Uveitis has been previously described in horses with CVID, particularly due to intraocular Borrelia infection. In people, autoimmune uveitis associated with CVID is well established. This report describes a case of bilateral presumed autoimmune uveitis in a 19‐year‐old Thoroughbred gelding with CVID. The diagnosis of CVID was made 8 months before the development of uveitis following recurrent episodes of bacterial pneumonia. Enucleation of the right eye was eventually performed due to severe uveitis and ocular pain refractory to medical management. Extensive infectious disease testing on aqueous humour and serum, as well as histopathology and immunohistochemistry, were performed. These diagnostics ruled out the presence of testable infectious organisms as the cause of uveitis in this immunocompromised horse. Histopathology of the enucleated globe allowed for the immunopathology of the autoimmune uveitis in this patient with CVID to be described and for an informed prognosis to be determined. This report describes the first thoroughly investigated case of autoimmune uveitis presumed to be associated with CVID in a horse.