Encephalitis
Encephalitis is inflammation of the brain tissue (parenchyma) and can develop from viral, bacterial, fungal or parasitic causes or from autoimmune mechanisms. Viral encephalitis is the most common form; Herpes Simplex Virus (HSV) is the most important sporadic cause and carries the highest mortality and morbidity. Typical features are fever, headache, altered consciousness, seizures and focal neurological deficit. When suspected, urgent aciclovir treatment should be started without waiting for a diagnosis.
Última atualização: 2026-06-07
Definition and Causes
Encephalitis is inflammation of the brain parenchyma resulting in neuronal dysfunction/damage; it may present as meningoencephalitis when the meninges are also involved. The most common causes are viruses: Herpes Simplex Virus (HSV-1), Varicella-Zoster, enteroviruses and mosquito/tick-borne arboviruses (West Nile, Japanese encephalitis, tick-borne encephalitis). Less commonly, bacterial, fungal and parasitic causes play a role. In addition, non-infectious, antibody-mediated autoimmune encephalitides (for example anti-NMDA receptor encephalitis) form an important group.
Pathophysiology
Viruses reach the brain by retrograde spread along peripheral nerves (HSV-1: trigeminal nerve, olfactory pathway), via the bloodstream or by direct invasion. Viral replication in the brain parenchyma leads to damage in neurons and glial cells, an inflammatory response, cerebral edema and, in some cases (especially HSV), hemorrhagic necrosis. In HSV encephalitis, involvement is typically concentrated in the temporal lobe and limbic structures; this explains the memory and behavioral features of the disease.
Symptoms
A flu-like prodrome (fever, muscle pain, headache) is often seen. The most important finding is altered consciousness (drowsiness, confusion, and coma in severe cases). Seizures are common and may be accompanied by focal neurological deficit (weakness, speech disturbance, imbalance) and behavioral changes (agitation, psychotic features). In HSV encephalitis, memory impairment, aphasia, behavioral changes and olfactory/gustatory hallucinations due to temporal lobe involvement are prominent. In autoimmune encephalitis, psychiatric features, movement disorders and autonomic instability may come to the fore.
Diagnosis
Lumbar puncture with CSF analysis and brain magnetic resonance imaging (MRI) are essential for diagnosis. The CSF typically shows a lymphocyte-predominant rise in cells, mildly elevated protein and normal glucose. For the diagnosis of HSV encephalitis, CSF HSV PCR is the gold standard; however, because it may be negative in the first days, treatment is continued and the test repeated if clinical suspicion persists. MRI is superior for showing temporal lobe involvement in particular; a normal scan in the first 24-48 hours does not exclude encephalitis. EEG can show seizure activity and typical findings in HSV. When autoimmune encephalitis is suspected, autoantibodies are sought in blood and CSF.
Treatment
When Herpes Simplex Encephalitis is suspected, urgent intravenous aciclovir should be started without waiting for diagnostic tests, because delay in treatment increases mortality and permanent damage. Aciclovir treatment usually lasts 14-21 days and is given with monitoring of kidney function and adequate fluids. In other viral causes such as CMV, appropriate antivirals are used, and in autoimmune encephalitis, immunotherapy (corticosteroids, intravenous immunoglobulin, plasma exchange and, when needed, second-line drugs); in the presence of an associated tumor (for example an ovarian teratoma in anti-NMDA encephalitis), removal of the tumor is part of treatment. Supportive care includes seizure control, management of intracranial pressure and respiratory support when needed.
Prevention and Prognosis
Prevention is possible for some forms of encephalitis: Japanese encephalitis and tick-borne encephalitis vaccines, post-exposure prophylaxis for rabies, and protection against mosquitoes/ticks are effective measures. In HSV encephalitis, prognosis is closely linked to early initiation of treatment; mortality is very high without treatment and is markedly reduced with aciclovir. A significant proportion of survivors may be left with sequelae such as memory impairment, epilepsy and cognitive deficit. In autoimmune encephalitis the recovery rate with immunotherapy is high. Physical therapy and cognitive rehabilitation are important in patients with neurological sequelae. Outcomes are individual and cannot be guaranteed.
Referências
- Greenberg MS. Greenberg's Handbook of Neurosurgery. 10th ed. Thieme; 2023:397-399.
- Venkatesan A, Tunkel AR, Bloch KC, et al. Case definitions, diagnostic algorithms, and priorities in encephalitis: consensus statement of the International Encephalitis Consortium. Clin Infect Dis. 2013;57(8):1114-1128.
- Tunkel AR, Glaser CA, Bloch KC, et al. The management of encephalitis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2008;47(3):303-327.
Este artigo é informativo e não substitui um exame médico. As decisões de diagnóstico e tratamento são individuais.