Neurological Feline Infectious Peritonitis (Neurological FIP)

Neurological FIP is a severe manifestation of feline infectious peritonitis (FIP), primarily affecting the central nervous system (CNS), with highly variable clinical signs and a challenging diagnosis.

Feline infectious peritonitis (FIP) is a fatal systemic inflammatory disease caused by a mutated strain of feline coronavirus (FIPV). While the most common forms are effusive and non-effusive FIP, approximately 5–10% of cases develop into neurological FIP, characterized by inflammatory lesions in the brain and spinal cord, leading to a range of neurological symptoms.

Pathogenesis of Neurological FIP

Neurological FIP occurs when the mutated FIP virus infects endothelial cells and macrophages within the CNS, disrupting the blood-brain barrier. This triggers inflammatory processes such as meningitis, ventriculitis, myelitis, and neuronal necrosis 【Pedersen, 2009】.

Studies have shown that viral RNA and immune complexes can be detected in cerebrospinal fluid (CSF) and nervous tissues in affected cats, indicating direct viral damage to neural tissue 【Crawford et al., 2017】.

Clinical Signs

The clinical manifestations of neurological FIP are highly variable, depending on the affected area (e.g., brainstem, cerebellum, spinal cord, optic nerve):

• Motor dysfunction: ataxia, unsteady gait, hind limb paralysis

• Behavioral changes: dullness, altered awareness, personality shifts

• Seizure-like episodes: tremors, muscle twitching, collapse

• Nystagmus (involuntary eye movement), head tilt

• Visual impairment or blindness

• Neck stiffness, lowered head posture

• Coma in advanced stages

The disease often progresses rapidly, with severe cases leading to death within weeks.

Diagnostic Aids

Neurological FIP lacks a single definitive marker but may be supported by the following findings:

CSF Analysis:

• Elevated protein concentration (>200 mg/dL)

• Mild mononuclear pleocytosis

• FCoV RNA detection (qPCR), immunohistochemistry, or FCoV antibodies

MRI Imaging:

• Ventricular enlargement, meningeal enhancement, inflammatory lesions in the cerebellum or brainstem

Blood Tests:

• Albumin:Globulin ratio (A:G) < 0.4

• Elevated total protein

• Elevated α1-acid glycoprotein (AGP)

Clinical Context:

• Co-occurrence with other systemic signs of FIP (fever, anorexia, jaundice) increases diagnostic confidence

According to ABCD guidelines, diagnosis depends on clinical expertise and comprehensive interpretation of multiple findings 【Addie et al., 2015】.

Treatment Protocol

The emergence of GS-441524 antiviral agents has revolutionized the treatment of neurological FIP. Studies show that with appropriate dosing and treatment duration, recovery is possible.

• Recommended drug: NeoFipronis® (Generic name: Pronidesivir)

• Suggested dosage: 20–30 mg/kg/day for 84 consecutive days

• Oral tablets preferred over injectables to improve compliance

During treatment, the following parameters should be monitored:

• Neurological symptom changes (e.g., seizure frequency, gait improvement)

• Weight gain, body temperature normalization, improved appetite

• Biochemical indicators: A:G ratio, AGP levels, etc.

Studies report that some cats show marked improvement within weeks, with long-term remission rates reaching 70–80% 【Dickinson et al., 2020】.

Precautions

• Differentiate from other neurological diseases such as coronavirus encephalitis, feline leukemia virus, toxoplasmosis, and CNS lymphoma

• Treatment must be strictly supervised by a veterinarian to avoid underdosing or treatment interruption

• Severe cases may require supportive therapies: pain management, nutritional support, antiepileptic drugs

References

1. Pedersen NC. A review of feline infectious peritonitis virus infection: 1963–2008. J Feline Med Surg. 2009;11(4):225–258.

2. Crawford C, et al. Diagnosis and clinical characteristics of cats with neurological FIP. J Vet Intern Med. 2017;31(6):1470–1476.

3. Addie DD, et al. Feline infectious peritonitis: ABCD guidelines on prevention and management. J Feline Med Surg. 2015;17(7):570–582.

4. Dickinson PJ, et al. Antiviral treatment using GS-441524 in cats with neurological FIP. Vet J. 2020;263:105582.