Paediatrics chapters
Encephalitis
Inflammation of the brain tissue in children, mostly from viruses: the causes, how it differs from encephalopathy, the clinical picture, CSF, EEG and scan findings, and supportive and antiviral treatment.
- Encephalitis is inflammation of the brain parenchyma causing fever, altered consciousness, seizures and focal signs; it is mostly viral (enteroviruses, arboviruses, herpes simplex); encephalopathy is the same picture without inflammation (toxic or metabolic).
- CSF is clear with lymphocytes, mildly raised protein and normal glucose; EEG shows diffuse slow waves; a temporal lobe focus on EEG or imaging points to herpes simplex.
- Treatment is supportive (airway, seizures, raised ICP, fluids at about 60%), plus IV acyclovir for herpes simplex or varicella; HSV has the worst outcome.
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Overview
Encephalitis is inflammation of the brain tissue that disturbs brain function, usually with early loss of consciousness. It is mostly caused by viruses, either by direct invasion or by an immune reaction after an infection. Many cases have no virus identified (Nelson: about one third remain unexplained). The key practical point is to recognise herpes simplex encephalitis, because it is treatable and deadly if missed.
Definitions
| Term | Meaning |
|---|---|
| Encephalitis | Direct infection and inflammation of the grey matter |
| Meningoencephalitis | Brain and meninges both inflamed; any virus causing encephalitis can also cause meningitis |
| Post-infectious (parainfectious) encephalitis | Immune-mediated demyelination appearing days after a viral illness or vaccination |
| Encephalopathy | Encephalitis-like illness without fever or inflammation, due to toxic or metabolic causes |
| ADEM (acute disseminated encephalomyelitis) | Sudden multifocal neurological signs from inflammatory demyelination of brain and cord, after viral infections (measles, chickenpox) or vaccines; resembles multiple sclerosis |
Label a child as having encephalitis only after metabolic and toxic encephalopathies are excluded: Reye syndrome, hepatic encephalopathy, diabetic ketoacidosis, lead and hypertensive encephalopathy.
Aetiology
| Group | Examples |
|---|---|
| Enteroviruses | Coxsackie, echovirus, poliovirus (Nelson: the commonest overall) |
| Herpesviruses | Herpes simplex (commonest sporadic cause), varicella-zoster, EBV, CMV |
| Arboviruses (mosquito or tick) | West Nile, dengue, yellow fever; cause epidemics |
| Other viruses | Mumps, measles, rubella, rabies, HIV, adenovirus |
| Post-infectious | Measles, rubella, varicella, vaccinia |
| Non-viral | Mycoplasma, rickettsia, Lyme disease, cat-scratch, fungi, parasites |
- Arboviral and enteroviral encephalitis come in clusters in summer and autumn; herpes cases occur all year.
- Herpes simplex type 2 infects the newborn during vaginal delivery, causing skin vesicles and encephalitis.
Viral preference for brain regions
| Virus | Preferred site |
|---|---|
| Herpes simplex | Fronto-temporal lobes |
| Varicella | Cerebellum (acute cerebellar ataxia) |
| Mumps | Meninges (aseptic meningitis); also transverse myelitis |
| Polio | Anterior horn cells and brainstem |
Pathology
The brain is swollen and congested; an early neutrophil response gives way to lymphocytes and plasma cells around vessels, with neuronal degeneration and sometimes intranuclear inclusion bodies.
Clinical features
- Often a prodrome: sore throat, fever, headache, abdominal upset (Nelson).
- Sudden high fever and headache, then altered consciousness from drowsiness to deep coma; confusion, abnormal behaviour, irritability.
- Seizures (often at presentation).
- Focal signs: squint or facial palsy, aphasia, hemiplegia, ataxia, abnormal reflexes.
- Neck stiffness if the meninges are involved.
- Spinal cord involvement: spastic paraplegia with loss of bladder and bowel control.
- Infants: gross irritability and poor feeding rather than headache.
- Raised ICP: papilloedema, decerebrate posturing, tentorial herniation.
Special types
| Type | Key points |
|---|---|
| Herpes simplex | Fever, vomiting, lethargy, then coma and focal seizures; behaves like a temporal lobe mass (hemiparesis, focal fits, raised ICP); CSF may show red cells or xanthochromia |
| Measles | Starts 2 days to 2 weeks after the rash; CSF lymphocytes 50-250; may involve the cord; SSPE follows years later |
| Varicella | About 4-6 days after the rash; cerebellar ataxia typical |
| Mumps | Aseptic meningitis 2-3 days after parotitis; encephalitis 7-10 days later with seizures and coma |
| Polioencephalitis | In a small minority of polio cases; drowsiness, tremors, coma, fits with limb or bulbar paralysis; think of it in endemic areas |
Slow virus disease
- Appears months to years after infection with dementia, falling school performance and behaviour change.
- Examples: SSPE after measles, rubella, HIV; prion disease (Creutzfeldt-Jakob).
Fever with focal seizures and a temporal lobe lesion in a child is herpes simplex encephalitis. Start acyclovir without waiting for confirmation.
Investigations
| Test | Finding |
|---|---|
| CSF | Usually clear; cells from a few to several hundred (neutrophils early, lymphocytes later); protein mildly raised; glucose normal. Very high protein or low glucose suggests TB, fungus or malignancy |
| PCR of CSF | For herpes simplex, enteroviruses; faster and more sensitive than culture |
| EEG | Diffuse high-amplitude slow waves; Nelson calls it the definitive test. In herpes simplex: periodic slow complexes over the temporal region |
| CT or MRI | May be normal or show diffuse swelling; a temporal lobe lesion suggests herpes |
| Serology | Paired sera about 2 weeks apart, a fourfold rise confirms |
| Virus isolation | Blood, CSF, stool, throat |
| Blood tests | Count, glucose, electrolytes, smear for malaria; exclude bacterial infection |
| Brain biopsy | Rarely; for focal disease when the diagnosis is unclear |
Typical viral CSF: clear, lymphocytes, slightly raised protein, normal glucose. Herpes CSF may also contain red cells.
Differential diagnosis
Pyogenic and tuberculous meningitis, cerebral malaria, brain abscess, brain tumour, heat stroke, lead encephalopathy, Reye syndrome and other metabolic encephalopathies. Ask about recent measles, chickenpox or polio exposure, mosquito, tick or animal bites, recent vaccination, and heavy metal or pesticide exposure.
Management
Supportive care (most cases)
- Airway first; equipment for ventilation at hand; ICU care if deeply comatose.
- Seizures: IV or rectal diazepam, then phenobarbitone maintenance.
- Raised ICP and cerebral oedema (present in most): dexamethasone, mannitol, head elevation.
- Fluids restricted to about 60% of maintenance; avoid dextrose water or very dilute saline, which worsen brain swelling; watch for SIADH.
- Fever: paracetamol and tepid sponging.
- Nutrition by nasogastric tube.
- Antibiotics until bacterial meningitis is excluded.
- Nursing the comatose child: frequent suction, turning to prevent sores and deformity, eye, mouth, bladder and bowel care.
Specific treatment
| Cause | Treatment |
|---|---|
| Herpes simplex, varicella-zoster | IV acyclovir (drug of choice) |
| CMV | Ganciclovir |
| HIV | Antiretroviral therapy |
| Mycoplasma | Macrolide or doxycycline (benefit uncertain) |
| ADEM | High-dose IV corticosteroids |
| Rabies | No cure; prevent with pre- or post-exposure vaccine |
"Herpes Hits the Temporal lobe, Acyclovir Answers."
Low CSF glucose or very high protein does not fit viral encephalitis; think of tuberculous or fungal infection.
Avoid hypotonic fluids (dextrose water, very dilute saline) because they worsen brain oedema.
Complications
Hemiplegia, squint, deafness, intractable seizures and later epilepsy, intellectual disability, learning and behaviour problems, hydrocephalus, and complications of coma (bed sores, aspiration pneumonia, catheter-related urinary infection).
Prognosis
- Nelson: about two thirds recover fully; overall mortality is about 5%; residual paresis, ataxia, seizures or cognitive problems in the rest, which often improve over time.
- Worse outcome with herpes simplex (Akbar quotes a mortality above 70%), and in children under 1 year or who present in coma.
- Enteroviral encephalitis does better.
- Rabies is almost always fatal.
- ADEM relapses in about 14% and may be the first sign of multiple sclerosis.
Prevention
Mosquito and tick avoidance, measles, polio, varicella and influenza vaccination, rabies vaccine after bites, caesarean section when the mother has active genital herpes, and avoiding aspirin in febrile children (Reye syndrome).
Expect: herpes simplex as the commonest sporadic and most dangerous treatable cause; temporal lobe involvement on EEG and MRI; CSF lymphocytes with normal glucose; encephalopathy versus encephalitis (Reye syndrome, lead); acyclovir as treatment; varicella and cerebellar ataxia; measles encephalitis and SSPE; mumps meningitis; ADEM after infection or vaccine; fluid restriction and control of seizures and ICP; poor prognosis under 1 year and with coma.
Quick revision
- Brain parenchyma inflamed; fever, coma, seizures, focal signs.
- Enteroviruses and arboviruses in epidemics; HSV commonest sporadic cause.
- Encephalopathy: no inflammation; exclude Reye, DKA, lead, hepatic, hypertensive.
- CSF clear, lymphocytes, protein slightly up, glucose normal; PCR for HSV.
- EEG diffuse slowing; HSV temporal periodic complexes.
- IV acyclovir for HSV and varicella; supportive care for the rest.
- Restrict fluids to about 60%; avoid hypotonic fluids; treat seizures and ICP.
- Worst outcome: HSV, infants, coma.
Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics).
FAQ
What is the difference between encephalitis and encephalopathy?
Encephalitis is true inflammation of the brain, usually from infection. Encephalopathy gives a similar picture of altered consciousness and seizures but without inflammation, from toxic or metabolic causes such as Reye syndrome, lead or hepatic failure.
Why is herpes simplex encephalitis so important?
It is the commonest sporadic cause, has the highest mortality, and is the one form with an effective drug. Intravenous acyclovir should start as soon as it is suspected.
What does the CSF look like in viral encephalitis?
It is usually clear with a modest rise in lymphocytes, slightly raised protein and normal glucose. Red cells may be present in herpes simplex encephalitis.
What is ADEM?
Acute disseminated encephalomyelitis is an immune-mediated demyelinating illness of the brain and cord that follows a viral infection or vaccination. It is treated with high-dose corticosteroids.