Meningoencephalitis

Meningitis, encephalitis and meningoencephalitis

In practice, many infections affect both, and the distinction guides how urgently doctors look for brain involvement.

Causes

Viral (most common)

• Herpes simplex virus (HSV-1): the most common cause of severe sporadic viral encephalitis in the US; often affects the temporal lobes, causing confusion, personality change, speech problems and seizures.
• Enteroviruses: especially in summer and autumn, and in children.
• Varicella-zoster virus: after chickenpox or shingles.
• Arboviruses: West Nile virus and others spread by mosquitoes or ticks.
• Others: HIV, mumps, measles, influenza, rabies.

Bacterial

• Streptococcus pneumoniae, Neisseria meningitidis, Listeria (in newborns, older adults, pregnancy and weakened immunity), tuberculosis, syphilis, Lyme disease.

Fungal and parasitic

• Cryptococcus in people with HIV or immunosuppression
• free-living amoebae such as Naegleria fowleri (rare, from warm freshwater entering the nose)
• toxoplasmosis

Autoimmune

Autoimmune encephalitis, such as anti-NMDA receptor encephalitis, can follow infection or occur with tumors, causing psychiatric symptoms, seizures and movement problems.

Symptoms

• fever
• severe headache
• stiff neck and pain bending the head forward
• sensitivity to light (photophobia)
• nausea and vomiting
• confusion, disorientation and drowsiness
• personality or behavior changes, hallucinations
• seizures
• weakness, numbness, speech or vision problems
• in babies: fever or low temperature, irritability, poor feeding, floppiness, a bulging fontanelle

Diagnosis

• lumbar puncture: cerebrospinal fluid is tested for cells, protein, glucose, bacteria and viral PCR (including HSV). This is the key test.
• brain MRI: shows areas of inflammation; HSV typically affects the temporal lobes. A CT scan may be done first if there are signs of raised pressure.
• EEG: detects seizure activity and abnormal brain function.
• blood tests and cultures, HIV test, and tests for specific infections based on travel and exposures
• autoimmune antibody tests in blood and spinal fluid if infection is not found

Treatment

Treatment starts immediately, often before test results:

• IV acyclovir: for possible HSV or varicella-zoster encephalitis. Delays worsen outcomes.
• IV antibiotics: such as ceftriaxone and vancomycin, plus ampicillin when Listeria is possible, until bacterial infection is excluded.
• Steroids: dexamethasone in some bacterial meningitis cases.
• Supportive care: fluids, fever control, anti-seizure medicines, management of brain swelling, sometimes intensive care.
• Targeted treatment once the cause is found: antifungals, anti-tuberculosis drugs, or immunotherapy (steroids, IVIG, plasma exchange) for autoimmune causes.

Complications and recovery

Depending on the cause and speed of treatment, people may have:

• memory and concentration problems
• personality or mood changes
• epilepsy
• hearing loss (especially after bacterial meningitis)
• weakness, speech or coordination problems

Rehabilitation with physical, occupational, speech and neuropsychological therapy supports recovery, which can continue for months to years.

Prevention

• vaccines: MMR, varicella, pneumococcal, meningococcal, Hib, Japanese encephalitis and tick-borne encephalitis when traveling to risk areas
• mosquito and tick bite prevention: repellents, long sleeves, removing standing water
• food safety in pregnancy to avoid Listeria (avoid unpasteurized dairy and deli meats unless heated)
• avoiding putting your head under warm freshwater in high-risk areas

Frequently asked questions

What is meningoencephalitis?

Meningoencephalitis is inflammation of both the brain and the meninges, the membranes surrounding it. It is usually caused by infection, especially viruses, but bacteria, fungi, parasites and autoimmune conditions can also cause it.

What are the symptoms of meningoencephalitis?

Symptoms include fever, severe headache, stiff neck, sensitivity to light, vomiting, confusion, behavior change, drowsiness and seizures. Babies may be floppy, irritable and feed poorly. It is a medical emergency.

How is meningoencephalitis treated?

Doctors start IV acyclovir and antibiotics immediately, before test results, to cover the most dangerous treatable causes. Treatment is then adjusted to the cause, with supportive care for seizures, brain swelling and hydration.

Can you fully recover from meningoencephalitis?

Many people recover fully, especially with prompt treatment and milder viral causes. Others have lasting memory, mood, seizure or movement problems. Rehabilitation helps, and improvement can continue for a long time.