Feline Meningoencephalitis: Causes, Neurological Signs and Emergency Care

1. Pathophysiology: Inflammation within the Cranial Vault

The meninges (dura, arachnoid, and pia mater) protect the central nervous system. When infectious organisms or autoimmune reactions penetrate the blood-brain barrier, intense inflammatory cell infiltration ensues.

Because the feline brain resides within a non-distensible bony cranium (Monro-Kellie doctrine), inflammatory exudate and vasogenic edema cause an immediate surge in intracranial pressure, precipitating brain tissue ischemia and life-threatening transtentorial or foramen magnum herniation.

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2. Primary Etiologies in Feline Practice

The diagnostic search centers on infectious pathogens:

• Neurological Feline Infectious Peritonitis (FIP): The leading cause. Mutated feline coronavirus drives immune-complex vasculitis and pyogranulomatous ependymitis and leptomeningitis.
• *Fungal Meningoencephalitis (Cryptococcus neoformans/gattii):* Enters via cribriform plate erosion from nasal granulomas.
• *Toxoplasmosis (Toxoplasma gondii):* Encephalic tachyzoite proliferation causing multifocal necrosis.
• Bacterial Meningitis: Ascending spread from deep otitis media/interna, bite wound abscesses, or systemic septicemia.
• Meningoencephalitis of Unknown Origin (MUO): Uncommon non-infectious autoimmune presentations diagnosed strictly by exclusion.

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3. Clinical Presentation: Rigidity, Ataxia, and Altered Mentation

Multifocal central nervous system signs characterize the disorder:

• Cervical hyperesthesia and neck rigidity: Severe pain and muscle guarding when the neck is flexed or extended; reluctance to lower the head to food bowls.
• Vestibular and cerebellar signs: Pathological nystagmus (involuntary eye darting), head tilt, broad-based ataxia, and intention tremors.
• Forebrain signs: Generalized or focal epileptic seizures, compulsive pacing, head pressing against hard surfaces, and central blindness.
• Pyrexia and progressive obtundation advancing into coma.

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4. Advanced Diagnostic Workup: MRI and CSF Analysis

Confirming central nervous system inflammation requires tertiary diagnostics:

• Magnetic Resonance Imaging (MRI): Demonstrates meningeal contrast enhancement, periventricular inflammation, ventricular asymmetry (hydrocephalus), or parenchymal granulomas.
• Cerebrospinal Fluid (CSF) Analysis: Performed via cisterna magna puncture under general anesthesia; reveals marked pleocytosis (elevated nucleated cells) and hyperproteinorrheia.
• Comprehensive Infectious Molecular PCR Panels: Targeted for FCoV RNA, Toxoplasma DNA, and Cryptococcal antigen latex agglutination.

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5. Emergency Hospitalization Protocols and Prognosis

Immediate clinical stabilization focuses on pressure reduction and pathogen eradication:

• Intracranial pressure (ICP) management: Mannitol (0.5-1.0 g/kg IV) or 3% hypertonic saline for impending herniation; levetiracetam to halt seizure activity.
• Pathogen-targeted protocols: For neurological FIP, the nucleoside analogue GS-441524 administered at high neurological dosages (10-15 mg/kg SC/PO); for cryptococcosis, high-dose fluconazole; for toxoplasmosis, clindamycin.
• Immunomodulation: Judicious use of corticosteroids (dexamethasone or prednisolone) to extinguish destructive inflammation.

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Scientific Sources and References

• Bradshaw, J. M., et al. (2004). Feline meningoencephalomyelitis: A review of 44 cases. J Feline Med Surg, 6(3), 159-168.
• Negrin, A., et al. (2017). Results of magnetic resonance imaging in 14 cats with meningoencephalomyelitis. J Small Anim Pract, 58(8), 458-465.
• Pedersen, N. C., et al. (2019). Efficacy and safety of GS-441524 for treatment of cats with FIP. J Feline Med Surg, 21(4), 271-281.