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.

In our case series of 24 cats with confirmed neurologic FIP, the most common neurologic deficits on presentation included abnormal mentation, tetraparesis, (4) Severe (10) The MRI findings were categorized as mild (no ventriculomegaly, focal contrast enhancement), moderate (mild to moderate ventriculomegaly, no or minimal mass effect, focal contrast enhancement), or severe (marked ventriculomegaly, moderate to severe mass effect, generalized contrast enhancement). Pathologic lesions were categorized as mild (focal inflammatory infiltrates), moderate (mild ventriculomegaly with multifocal infiltrates), or severe (marked ventriculomegaly with extensive infiltrates). pathologic nystagmus, and vestibular ataxia. Magnetic resonance imaging of the brain often identified marked enlargement of the fourth ventricle causing dorsal compression of the brainstem and ventral compression of the cerebellum. This compression may compromise the vestibular nuclei, vestibulocerebellum, or both, thus accounting for the high frequency of clinical vestibular deficits. Various mechanisms may contribute to abnormal mentation, including brainstem compression compromising the ascending reticular activating system, increased intracranial pressure causing diffuse forebrain compromise, or neuropathic pain secondary to syringomyelia. Tetraparesis may have resulted from compression of the descending upper motor neuron tracts as they traverse the brainstem and cervical spinal cord. Seven cats experienced acute deterioration to nonambulatory status before referral. Potential underlying mechanisms for this acute deterioration may include increased intracranial pressure leading to herniation or progression of systemic disease. Only 1 cat (4.2%) was reported to have had a possible seizure episode. However, a study of 55 cats with neurologic FIP reported the presence of seizures in 14 (25.5%) and found that seizures were significantly more frequent in cats with marked extension of the inflammatory lesions to the forebrain. 8 Histopathologic analysis of the brains of the cats in our study indentified inflammatory infiltrates extending into the brainstem parenchyma in 5 cats, and periventricular infiltration primarily around the lateral ventricles in 13 cats, with no clinically relevant extension into the cortical areas. The absence of cortical involvement may account for the much lower frequency of seizures in our case series.