Encephalitis lethargica

What it is

From: Orphanet

A rare brain inflammatory disease characterized by acute or subacute encephalitis with involvement of the midbrain and basal ganglia occurring in children as well as adults. Initial symptoms are pharyngitis and fever, followed by progressive lethargy, sleep disturbances, extrapyramidal symptoms (parkinsonism, chorea, dystonia), neuropsychiatric manifestations (obsessive-compulsive behavior, mutism, catatonia), and ocular features (oculogyric crises). Autoantibodies against human basal ganglia are often positive. Survivors may develop post-encephalitic syndromes, most prominently parkinsonism.

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.

Encephalopathy · Very frequent (99-80%)

Encephalopathy is a term that means brain disease, damage, or malfunction. In general, encephalopathy is manifested by an altered mental state.

Sleep abnormality · Very frequent (99-80%)

An abnormal pattern in the quality, quantity, or characteristics of sleep.

Abnormal involuntary eye movements · Frequent (79-30%)

Anomalous movements of the eyes that occur without the subject wanting them to happen.

Autoimmunity · Frequent (79-30%)

The occurrence of an immune reaction against the organism's own cells or tissues.

Diplopia · Frequent (79-30%)

Diplopia is a condition in which a single object is perceived as two images, it is also known as double vision.

Dyskinesia · Frequent (79-30%)

A movement disorder which consists of effects including diminished voluntary movements and the presence of involuntary movements.

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.

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

Increased concentration of protein in the cerebrospinal fluid.

Increased circulating immunoglobulin concentration · Frequent (79-30%)

An increased level of gamma globulin (immunoglobulin) in the blood.

Lethargy · Frequent (79-30%)

A state of fatigue, either physical or mental slowness and sluggishness, with difficulties in initiating or performing simple tasks. Distinguished from apathy which implies indifference and a lack of desire or interest in the task. A person with lethargy may have the desire, but not the energy to engage in personal or socially relevant tasks.

Mental deterioration · Frequent (79-30%)

Loss of previously present mental abilities, generally in adults.

Myalgia · Frequent (79-30%)

Pain in muscle.

Parkinsonism · Frequent (79-30%)

Characteristic neurologic anomaly resulting from degeneration of dopamine-generating cells in the substantia nigra, a region of the midbrain, characterized clinically by shaking, rigidity, slowness of movement and difficulty with walking and gait.

Other findings in the same source

From: Orphanet

Additional reported features include Pharyngitis (Frequent (79-30%)); Recurrent viral infections (Frequent (79-30%)); Tremor (Frequent (79-30%)); Upper limb muscle weakness (Frequent (79-30%)); Bilateral basal ganglia lesions (Frequent (79-30%)); Limitation of neck motion (Frequent (79-30%)); Bowel incontinence (Occasional (29-5%)); Bradycardia (Occasional (29-5%)); Coma (Occasional (29-5%)); Hyperventilation (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

When it may begin

From: Orphanet

Adult

Inheritance in the source

From: Orphanet

Not applicable

Which doctor should you see?

The suggested department for discussing Encephalitis lethargica 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.

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

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Encephalitis lethargica. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

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.