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.

F eline infectious peritonitis (FIP) is the most common infectious disease of the central nervous system (CNS) in cats, typically affecting animals <3 years of age from multicat environments. [1] [2] [3] [4] Although the pathogenesis is complex and incompletely understood, the causative agent, FIP virus (FIPV), is a monocyte/ macrophage-tropic mutant of the ubiquitous feline enteric coronavirus (FECV). 5, 6 Virus-laden macrophages trigger a marked inflammatory reaction, resulting in multisystemic pyogranulomatous vasculitis. With time, the histiocytic population is replaced by a lymphoplasmacytic population. Two forms of the disease are recognized, the effusive or "wet" form, associated with serous exudates into the abdominal cavity, and the noneffusive or "dry" form, associated with granulomatous parenchymal lesions. 7 Approximately 38% of cases with the noneffusive form and 5% of cases with the effusive form of FIP are presented with involvement of the CNS, in which typical neurologic deficits are reported, including seizures, ataxia, and head tilt. 4, 5, 7, 8 The inevitable mortality of CNS FIP necessitates prompt diagnosis to avoid prolonged efforts at unsuccessful treatment and inappropriate client expectations. However, antemortem definitive diagnosis of the disease remains challenging because FIPV is serologically and genetically indistinguishable from FECV, and hence, further diagnostic tools are needed. 1 Within the CNS, FIPV-induced pyogranulomatous vasculitis predominantly affects the leptomeninges, ependyma, and choroid plexuses. 2, 5, 6, 9 Such lesions would be expected to generate distinctive changes on MRI of the CNS. The MRI findings in 4 cats with neurologic FIP were previously reported. 5 Ventricular dilatation was detected in 3 cats, with periventricular contrast enhancement in all cats in which contrast agents were administered. In a subsequent study, 8 cats with histologically confirmed neurologic FIP and MRI were reported. 10 In 3 cases, MRI was reported to be normal. In the remaining 5 cases, abnormalities included cerebellar herniation (3), ventricular dilatation (4) , and meningeal and ependymal contrast enhancement (5) . Therefore, although MRI abnormalities have been documented in cats with neurologic FIP, case numbers are limited. Furthermore, advances in MRI technology and availability since these prior publications have made it an increasingly sensitive and accessible diagnostic tool. The aim of our study was to collate a larger number of cases to further evaluate neurologic FIP, with particular emphasis on assessing and comparing the clinical presentation with the MRI features and pathologic lesions.