Clinicopathologic Features and Magnetic Resonance Imaging Findings in 24 Cats With Histopathologically Confirmed Neurologic Feline Infectious Peritonitis

Crawford, A.H.; Stoll, A.L.; Sanchez-Masian, D.; Shea, A.; Michaels, J.; Fraser, A.R.; Beltran, E.

All 11 cases in which CSF was analyzed were found to have both increased total protein concentration and increased total nucleated cell count. These findings are in contrast to the limited abnormalities detected on peripheral blood analysis, including increased serum globulin concentration in 18% of cases, mild neutrophilia in 14%, and mild leukocytosis in 9%. Neutrophilic pleocytosis was the most common CSF cytologic finding, with some cats having lymphocytic or mixed pleocytosis. The cats with lymphocytic and mixed pleocytosis may reflect a more chronic stage of the disease, in which lymphoplasmacytic infiltrates begin to replace histiocytes and neutrophils. These results contradict the findings of a previous study, in which CSF was normal in a proportion of cases with confirmed neurologic FIP. 5 This difference may be explained by sample collection at an earlier stage of the disease pathogenesis, the presence of focal lesions, or both in the previous study. 20 Additionally, sample collection site may influence results because lumbar CSF samples typically have a higher protein concentration and decreased white blood cell count compared with samples collected from the cerebellomedullary cistern. 21 Neurologic FIP typically causes diffuse vasculitis affecting the brain and spinal cord, but cats may present with neurologic deficits suggestive of a more localized disease process. One cat in our series that was presented with a T3-L3 myelopathy underwent spinal cord MRI only, with no imaging of the brain. Postmortem examination of this cat, however, identified a lymphoplasmacytic meningoencephalomyelitis with secondary ventriculomegaly. In a study of 205 cats with spinal cord disease, 33 were diagnosed with FIP. 2 Of these, only 8 were presented with neurologic deficits indicative of brain involvement in addition to the spinal cord disease, but 29 underwent subsequent histopathologic analysis of the brain, and lesions consistent with FIP were detected in all 29. Thus, cats presented with a T3-L3 myelopathy often have concurrent brain pathology and may progress clinically to show neurologic deficits consistent with forebrain or brainstem localization.