Herpes simplex virus encephalitis

What it is

From: Orphanet

A rare disorder caused by infection of the central nervous system by Herpes simplex virus (HSV) that could have a devastating clinical course and a potentially fatal outcome particularly with delay or lack of treatment. This disorder often involves the frontal and temporal lobes, usually asymmetrically, resulting in personality changes, cognitive impairment, aphasia, seizures, and focal weakness.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of brain morphology · Very frequent (99-80%)

A structural abnormality of the brain, which has as its parts the forebrain, midbrain, and hindbrain.

CSF lymphocytic pleiocytosis · Very frequent (99-80%)

An increased lymphocyte count in the cerebrospinal fluid.

EEG abnormality · Very frequent (99-80%)

Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp.

Reduced consciousness · Very frequent (99-80%)

Abnormally diminished level of attention, responsiveness, or wakefulness.

Abnormality of speech or vocalization · Frequent (79-30%)

An abnormality in the sound (volume) or cadence (rate) of speech.

Fatigue · Frequent (79-30%)

A subjective feeling of tiredness characterized by a lack of energy and motivation.

Fever · Frequent (79-30%)

Body temperature elevated above the normal range.

Headache · Frequent (79-30%)

Cephalgia, or pain sensed in various parts of the head, not confined to the area of distribution of any nerve.

Hyponatremia · Frequent (79-30%)

The concentration of sodium in the blood circulation is below the lower limit of normal.

Increased CSF protein concentration · Frequent (79-30%)

Increased concentration of protein in the cerebrospinal fluid.

Increased total leukocyte count · Frequent (79-30%)

An abnormal increase in the number of leukocytes in the blood.

Loss of consciousness · Frequent (79-30%)

Loss of awareness of oneself or one's surroundings, involving (i) a loss of normal motor control is evident as flaccidity or stiffness, either of which can be accompanied by jerking movements, and postural control is lost so that patients fall if they are in an upright position; (ii) normal responsiveness is lost; and (iii) the patient experiences amnesia for the event. Loss of consciousness my be transitory (e.g., syncope) or prolonged.

Nausea and vomiting · Frequent (79-30%)

Nausea is a commonly encountered symptom that has been defined as an unpleasant painless subjective feeling that one will imminently vomit. Vomiting has been defined as the forceful expulsion of the contents of the stomach, duodenum, or jejunum through the oral cavity. While nausea and vomiting are often thought to exist on a temporal continuum, this is not always the case. There are situations when severe nausea may be present without emesis and less frequently, when emesis may be present without preceding nausea.

Neutrophilia · Frequent (79-30%)

Abnormal increase of absolute number of neutrophils in the blood, per microliter, compared to a reference range for a given sex and age-group.

Other findings in the same source

From: Orphanet

Additional reported features include Nuchal rigidity (Frequent (79-30%)); Respiratory failure requiring assisted ventilation (Frequent (79-30%)); Seizure (Frequent (79-30%)); Alcoholism (Occasional (29-5%)); Cerebral edema (Occasional (29-5%)); Chills (Occasional (29-5%)); Coma (Occasional (29-5%)); Elevated circulating C-reactive protein concentration (Occasional (29-5%)); Excessive daytime somnolence (Occasional (29-5%)); Focal aware seizure (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

When it may begin

From: Orphanet

All ages

Inheritance in the source

From: Orphanet

Multigenic/multifactorial; Not applicable

Frequency and the population described

From: Orphanet

Annual incidence: 1-9 / 1 000 000; Worldwide; Value and class. Annual incidence: 1-9 / 1 000 000; United Kingdom; Value and class. Annual incidence: 1-9 / 1 000 000; United States; Value and class.

Which doctor should you see?

The suggested department for discussing Herpes simplex virus encephalitis is Infectious Diseases, with a general physician / infectious disease specialist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which exposure or organism is suspected, and what evidence would confirm it?
• Are precautions, vaccination or advice for close contacts relevant to this infection?
• What should happen if symptoms worsen or do not improve as expected?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.