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Encephalitis is inflammation of the brain parenchyma, most commonly caused by viral infections such as herpes simplex virus, arboviruses, or enteroviruses. It presents with altered mental status, fever, headache, and neurological deficits, requiring urgent medical attention and antiviral therapy when indicated.
Viral or other pathogens cross the blood-brain barrier and directly invade brain tissue, triggering inflammatory responses that cause neuronal damage, cerebral edema, and disruption of normal brain function. The inflammatory cascade involves cytokine release, microglial activation, and immune cell infiltration that can lead to both direct cytotoxic effects and secondary injury from increased intracranial pressure.
Early recognition is critical as encephalitis can rapidly progress to coma, seizures, and death without prompt treatment. CSF analysis showing pleocytosis with lymphocytic predominance, elevated protein, and PCR testing for viral pathogens helps confirm diagnosis. Empirical acyclovir should be initiated immediately when HSV encephalitis is suspected, as delayed treatment significantly worsens neurological outcomes.
Key imaging focus: CT to rule out mass/midline shift before LP; MRI shows meningeal enhancement