Encephalitis is a pathological state of brain parenchymal dysfunction leading to an altered state of consciousness or focal neurological signs. It is a serious, complex, and potentially fatal disorder with non-infectious and infectious causes. Encephalitis presents with serious, complex, and potentially fatal disorder with non-infectious and infectious causes. Investigations should include blood cultures, neuroimaging (preferably magnetic resonance imaging), and cerebrospinal fluid analysis.
In all cases of suspected viral encephalitis, it is imperative to administer Aciclovir as soon as possible. Failure to do so may result in complications such as seizures, hydrocephalus, and neurological sequelae, such as motor problems and behavioural disturbances. Encephalitis, which is characterized by inflammation of the brain parenchyma and associated neurological dysfunction, may manifest as altered state of consciousness, personality changes, cranial nerve palsies, speech difficulties, and sensory and motor deficits. (Venkatesan A et al 2019).
Encephalitis is characterized by inflammation of the brain tissue, which is different from meningitis, where the inflammation occurs in the meninges. Encephalitis can be caused by infectious or non-infectious factors, and only about 50% of cases have a known causative agent (Granerod J et al 2010).
HSV-1 is the primary cause of herpes encephalitis, and the lesions typically occur in one of the temporal lobes. The destruction of the temporal lobe is caused by viral and immunopathological processes, leading to erythrocytes in the cerebrospinal fluid, seizures, focal neurologic abnormalities, and other signs of viral encephalitis. HSV is the most prevalent viral cause of sporadic encephalitis and can cause severe morbidity and mortality, even when patients receive appropriate treatment.
Encephalitis is primarily caused by viruses, with the herpes virus being the most frequently identified group of viruses. Whilst in immunocompromised individuals, the cytomegalovirus (CMV) encephalitis is a consideration.
In cases where community-acquired viral encephalitis is suspected, patients are started on empirical treatment with aciclovir until the underlying cause is identified. (Soloman T et al 2012).
Since the majority of sporadic viral encephalitis cases are caused by HSV, this clinical practice is supported by randomized controlled trials that have been proven by biopsy, and it has been shown to decrease mortality rates. (Whitley RJ et al 1986).
In both children and adults, a delayed initiation of treatment beyond 48 hours after hospital admission is linked with a poorer outcome (Kneen R et al 2012). Patients with suspected community-acquired viral encephalitis are treated empirically with aciclovir until the underlying cause is identified.
The treatment of choice is acyclovir and should be administered via IV at 10mg/kg every 8 hours for 10-21 days.
Aciclovir is an antiviral drug that belongs to the guanine analogue class and is effective against the herpes virus family. It is classified as a prodrug, and it requires phosphorylation by a virus-specific thymidine kinase to become active. This enzyme is found in most Herpesviridae but not in human cells, thus limiting its toxicity to host cells. However, since CMV lacks thymidine kinase, aciclovir is less effective against it. In such cases, ganciclovir is a better option as it is not dependent on a virus-specific thymidine kinase for phosphorylation, and it can eliminate all Herpesviridae, including CMV.
References:
Granerod J, Tam CC, Crowcroft NS, et al. Challenge of the unknown: a systematic review of acute encephalitis in non-outbreak situations. Neurology. 2010 Sep 7;75(10):924-32.
Kneen R, Michael BD, Menson E, et al. Management of suspected viral encephalitis in children – Association of British Neurologists and British Paediatric Allergy, Immunology and Infection Group national guidelines. J Infect. 2012 May;64(5):449-77.
Solomon T, Michael BD, Smith PE, et al. Management of suspected viral encephalitis in adults–Association of British Neurologists and British Infection Association National Guidelines. J Infect. 2012 Apr;64(4):347-73.
Venkatesan A, Michael BD, Probasco JC, et al. Acute encephalitis in immunocompetent adults. Lancet. 2019 Feb 16;393(10172):702-16.
Whitley RJ, Alford CA, Hirsch MS, et al. Vidarabine versus acyclovir therapy in herpes simplex encephalitis. N Engl J Med. 1986 Jan 16;314(3):144-9.
