Differential Diagnosis and Rapid Clinical Resolution of a Neurological Case of Feline Infectious Peritonitis (FIP) Using GS441524

A 2-year-old male neutered domestic shorthair cat was presented with a progressive history of tetraparesis, ataxia, and inappetence over 4 days. A physical exam revealed mucopurulent nasal discharge and stertor. Neurologic exam revealed a multifocal neurolocalization. The cat was non-ambulatory tetraparetic and developed seizures while in-hospital. Hematologic assessment revealed anemia, hypoalbuminemia and hyperglobulinemia. Magnetic resonance imaging (MRI) of the brain revealed multifocal meningeal contrast enhancement in the brainstem and cervical spine, as well as mandibular and retropharyngeal lymphadenopathy. Cerebrospinal fluid revealed marked neutrophilic pleocytosis, no infectious organisms were seen. Toxoplasma IgG/IgM and cryptococcus antigen latex agglutination were negative. Mandibular and abdominal lymph nodes were aspirated, and cytology revealed mixed inflammation. Nanopore sequencing specifically identified FCoV-1 RNA in spinal fluid and anal swab, but not in urine. This method serves as a novel and rapid PCR sequencing technique for the antemortem diagnosis of feline infectious peritonitis. The cat was treated with anticonvulsants (phenobarbital and levetiracetam), an antibiotic (ampicillin/clavulanic acid), and GS-441524. Neurologic signs did not improve on an antibiotic alone but improved significantly after two subcutaneous injections of GS-441524. The cat received an 84-day course of GS-441524 and, at the time of manuscript preparation (over 12 months after diagnosis), remained ambulatory and seizure-free without recurrence of neurologic signs and no detectable viral shedding in feces.