2. The cat's right eye had anterior synechić and fibrin in the pupil.

The rest of the physical examination findings were normal, and the cat weighed 11.9 lb (5.4 kg).

DIFFERENTIAL DIAGNOSES

The most common intraocular primary neoplasms are iris melanoma or ciliary body adenocarcinoma.¹ Ocular neoplasia can also result from metastatic cancer, most commonly lymphosarcoma.

Viral causes of uveitis in cats include feline infectious peritonitis (FIP), FeLV, and FIV infections. Cryptosporidiosis, blastomycosis, histoplasmosis, coccidioidomycosis, and, rarely, candidiasis should be considered depending on the region.⁴ The algae Prototheca species can also cause uveitis.¹ Bacterial causes include Bartonella, Mycoplasma, and Ehrlichia species.⁴ Toxoplasmosis is a common protozoal cause, which often leads to posterior segment disease, including chorioretinitis and pars planitis.⁵ Bartonella henselae and herpesvirus infection have also more recently been implicated as causing uveitis.⁶ While characteristic signs of specific infectious diseases exist (e.g. pars planitis and chorioretinitis caused by toxoplasmosis), studies have shown that intraocular changes are often indistinguishable among various infectious diseases.⁷

Specific immune-mediated diseases in the eye include lens-induced uveitis (phacoclastic uveitis), Vogt-Koyanagi-Harada-like syndrome, and immune-mediated vasculitis. Immune-mediated causes tend to be a diagnosis of exclusion. However, many systemic inflammatory responses (including systemic infection) can also lead to a secondary immune-mediated uveitis. For example, no infectious agents may be identified in the aqueous humor after anterior chamber paracentesis, but uveitis is still present because of systemic infection and activated T cells that have migrated back to the eye.⁸

A systemic infection was suspected in this cat because there was no known history of trauma, the ocular disease had progressed, and the cat was lethargic and inappetent. The differential diagnoses were bartonellosis, toxoplasmosis, and FIP, FIV, or FeLV infection (although the test results for FIV and FeLV were negative). Other infectious agents were less likely since the cat lived in Colorado⁹ and had no history of travel.

The cat had no intraocular mass and no blood work or thoracic radiograph abnormalities that suggested neoplasia. Because the uveitis was bilateral and the patient had mild lethargy and lymphocytosis, the cause was likely to be idiopathic, immune-mediated, or a manifestation of a systemic disease such as an infection.

DIAGNOSTIC TESTS

The patient was anesthetized, and anterior chamber paracentesis was performed. Atraumatic tissue forceps were used to grasp the bulbar conjunctiva, and a 27-ga needle was inserted through the perilimbal conjunctiva and limbal cornea to aspirate a small amount of aqueous humor.¹ PCR testing was done on the aspirate to evaluate for fip infection and bartonellosis.

In addition, serum was submitted for protein electrophoresis to distinguish between a monoclonal and polyclonal gammopathy as a cause of the cat's elevated globulin concentration. A polyclonal gammopathy is expected in patients with inflammatory or infectious conditions, especially chronic infections, toxoplasmosis, or FIP infection. A monoclonal gammopathy is consistent with some types of neoplasia, such as multiple myeloma. Serum was also submitted to evaluate the cat's antibody titer against Toxoplasma species.