Navigating neurological re-emergence in feline infectious peritonitis: challenges and insights from GS-441524 and remdesivir treatment.

Case summary: A 6-month-old male British Longhair cat presented with acute neurological signs, ocular changes, massive ascites and laboratory parameters consistent with feline infectious peritonitis (FIP). Systemic and neurological signs fully resolved with initial treatment (GS-441524; BOVA UK [15 mg/kg PO q24h for 42 days], levetiracetam [20 mg/kg q8h] and prednisolone [1 mg/kg q24h until day 21]). Lethargy and fever reappeared 17 days after treatment. Four days later, severe multifocal neurological signs re-emerged. High-field MRI revealed multifocal intra-axial and intramedullary lesions in the brainstem and cervical spinal cord, severe meningitis and generalised mild ventriculomegaly. Feline coronavirus (FCoV) RNA was detected in the cerebrospinal fluid by reverse transcription quantitative PCR (RT-qPCR). Abdominal effusion was absent. Serum alpha-1-acid glycoprotein (AGP) was again elevated. FIP re-emergence was suspected, and antiviral treatment was resumed. After 1 day of GS-441524 treatment (15 mg/kg PO q24h), severe hypoventilation developed, requiring intubation and mechanical ventilation for 1.5 days. Treatment was switched to remdesivir (16.7 mg/kg IV q24h, Veklury; Gilead) for 4 days. Oral GS-441524 was then reintroduced (10 mg/kg q12h) and continued until day 84. Treatment resulted in partial recovery with moderate ataxia and reduced left-sided menace response remaining 181 days after starting the second treatment. Relevance and novel information: This case illustrates the complexity of diagnosing and treating re-emerging FIP-associated neurological signs. AGP monitoring offers a promising non-invasive approach for early detection of relapse. By adapting short- and long-term antiviral treatment and providing intensive care, excellent long-term outcomes can be obtained for cats with severe relapsing FIP-related neurological signs.