Clinical and imaging findings after antiviral treatment in cats with presumptive neurologic feline infectious peritonitis: 9 cases (2020-2024).

Post-treatment imaging findings in neurologic FIP do not reliably reflect clinical outcomes and must be interpreted alongside patient status.

This retrospective, multicenter case series evaluated post-treatment imaging findings and clinical outcomes in 9 cats with presumptive neurologic feline infectious peritonitis (FIP) treated with antiviral therapy. Cases were collected from 8 institutions between January 2020 and December 2024. All cats underwent advanced imaging (MRI or CT) before and after treatment with GS-441524, remdesivir, or both, and all received concurrent corticosteroids. Central vestibular disease was the most frequent neuroanatomical localization (6/9 cats). Obstructive hydrocephalus was identified in all cats on both initial and follow-up imaging. CSF analysis, performed in 4 cats, revealed pleocytosis that was predominantly neutrophilic. Complete clinical recovery was achieved in 5/9 cats, while 4/9 had residual neurologic deficits and 2/9 experienced recurrence of neurologic signs. Critically, no cat demonstrated complete resolution of imaging abnormalities on follow-up studies. In 4/9 cats, obstructive hydrocephalus progressed on post-treatment imaging, including in some cats that showed clinical improvement. Imaging changes did not consistently correlate with clinical outcomes, highlighting a clinically important dissociation between radiologic findings and patient status. The authors conclude that post-treatment MRI or CT findings—particularly persistent or worsening obstructive hydrocephalus—should be interpreted in conjunction with the patient's clinical status rather than used as the sole measure of therapeutic response in cats with neurologic FIP receiving antiviral treatment.

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