Clinical and clinicopathologic features of an undifferentiated resolving uveitis in kittens similar to that seen with feline infectious peritonitis

Objective: To highlight clinical and clinicopathologic differences between kittens with feline infectious peritonitis-associated uveitis (FIP-AU) versus those with an otherwise similar feline undifferentiated resolving uveitis (FURU). Methods: Clinical and clinicopathologic data were compared between 22 kittens with FURU and 8 with necropsy-confirmed FIP-AU examined between January 1, 1985, and December 31, 2022. Results: Sex, lifestyle, seasonality, household cat numbers and systemic signs were similar in both groups. Feline undifferentiated resolving uveitis occurred predominantly in domestic-breed kittens from shelters, whereas FIP-AU was more frequent in purebred or stray cats. Duration of ocular signs before presentation was 1 to 2 weeks for FURU versus > 2 months for FIP-AU. Feline undifferentiated resolving uveitis was more commonly associated with episcleral hyperemia while FIP-AU was more commonly associated with corneal edema, dyscoria, rubeosis iridis, iridal congestion/thickening, posterior synechia, or keratic precipitates. Corneal edema and chemosis were more severe in FIP-AU. No eyes with FURU had fundic abnormalities whereas 6 of 11 eyes with FIP-AU had chorioretinitis. All kittens with FIP-AU presented bilaterally whereas 5 of 15 kittens in which FURU was ultimately bilateral, initially presented unilaterally. Hyperproteinemia, hyperglobulinemia, and hyperbilirubinemia occurred only with FIP-AU. Neither likelihood of a positive coronavirus titer nor titer magnitude differed between groups. Conclusions: Kittens can develop bilateral fibrinous uveitis with keratic precipitates, systemic signs of illness, and serum coronavirus antibodies which resolves without sequelae following empirical treatment. Syndromic assessment-including careful fundic examination-can help differentiate FURU from FIP-AU and should precede antiviral therapy. Clinical Relevance: Resolution of uveitis during antiviral treatment does not confirm FIP. Comprehensive diagnostic evaluation is essential to avoid misdiagnosis and inappropriate treatment.