Jamie was a twenty-two year old girl who had just had her first attack of genital Herpes simplex type 2 eight months ago. This resulted in a rapid onset herpes encephalitis within five days of the rash appearing, despite Josie being given three 500mg tablets stat of Famciclovir within forty-eight hours of symptoms, she had then continued on with famciclovir 500mg bd until hospitalisation. Josie ceased the famciclovir after six months and within a week had developed genital herpes again. She has been told she will need to stay on famciclovir indefinitely.
Herpes simplex encephalitis is a rare but very concerning complication of herpes infection, from either type 1 or type 2. Herpes simplex is a virus with double stranded DNA. Approximately one third of cases occur from the initial herpetic infection but the remaining two-thirds occur in patients who have reactivation of the herpes virus. Many doctors are familiar with this risk at childbirth if the mother develops the initial infection just prior to or within a short time of vaginal delivery. If so, caesarean section will avoid the risk of generalised encephalitis in addition to possible systemic infection in the neonate. Herpes encephalitis is most uncommon in older babies and children and the risk increases with age. In children over three months of age and in adults, the infection tends to affect the temporal and frontal lobes of the brain and can be difficult to diagnose (the herpetic lesions, if obvious, will suggest the possibility).
The virus appears to travel to the brain via the infected neurones, especially from the face. The most common symptoms are fever, headache, seizures (three quarters are focal, one quarter generalised), vomiting, focal neurological signs (regional weakness, dysphasia, ataxia), papilloedema, altered consciousness and memory loss. HSV 1 may cause brain stem encephalitis and HSV 2 can cause myelitis. Not all cases are fulminant and acute. Herpes encephalitis may present as a subacute condition with psychiatric presentations or recurrent meningitis. Herpes meningitis is most commonly caused by HSV 2 and tends to be a much more benign, but frustrating illness. It relapses with outbreaks of herpes.
Herpes encephalitis is diagnosed by paired cerebrospinal fluid samples showing development of immunity to herpes simplex, or identification of herpes viral PCR in the cerebrospinal fluid. Attempts to culture the virus from cerebrospinal fluid are usually unsuccessful and not recommended. Brain biopsy is rarely done. If herpetic lesions are present, identification of virus via PCR testing should be performed. MRI scans are the preferred imaging technique.
Treatment includes antivirals, anticonvulsants and management of raised intracranial pressure, if required. The prognosis depends on how unwell the patient is at presentation. Comatose patients do poorly. Untreated patients have a high mortality and major neurological sequelae. Patients under age thirty years do best and the older the patient, generally the worse the prognosis. Typically, approximately 50% of patients have major neurological deficits and approximately 40% have minor deficits. Children have a high incidence of ongoing problems such as epilepsy and developmental delay.
1. Anderson, W. Herpes simplex encephalitis. Practice Essentials, Medscape.