Autoimmune encephalitis: symptoms and causes

What autoimmune encephalitis is

Encephalitis means swelling, or inflammation, of the brain. In autoimmune encephalitis, the immune system makes antibodies that attack proteins on or inside nerve cells. That attack is what causes the swelling and the symptoms.

The name covers several illnesses. Each one has its own immune target. In some, the target is a receptor on the surface of nerve cells, such as the NMDA receptor. In others, it's a protein inside the cell. Some people have a clear pattern of the illness even though no known antibody turns up.

A similar word, encephalopathy, gets mixed up with it. Encephalopathy means the brain isn't working as it should. It has many causes, such as liver disease, low oxygen, drugs, or toxins. Encephalitis is one narrower cause, where the brain is actually inflamed.

Viruses are the most common cause of encephalitis overall. An immune cause is less common, but it matters because it is often treatable. That's why doctors look for it when a person gets suddenly worse and no infection explains it.

Sources: Cleveland Clinic: autoimmune encephalitis; Cleveland Clinic: encephalopathy; MedlinePlus: encephalitis; Lancet Neurology: clinical approach to diagnosis.

Autoimmune encephalitis symptoms

Symptoms vary with the type, but they tend to show up as a cluster rather than one sign alone. Common ones include:

• Memory loss and trouble thinking clearly
• Confusion or a lower level of alertness
• Seizures, some of which don't respond well to seizure medicine
• Hallucinations, paranoia, agitation, or other new psychiatric symptoms
• Odd movements of the mouth, face, arms, or legs
• Trouble speaking, or problems with balance
• Changes in heart rate, blood pressure, breathing, or sleep

Many of these signs also come from infection, medicines, or mental health conditions. One sign alone doesn't point to this illness. What stands out is a fast change from how the person used to be.

In adults 45 and older, it can look like dementia. In one large study, 67 of 175 patients in that age group met the criteria for dementia. Fast decline, subtle seizures, and odd test results were the clues that pointed elsewhere.

Families often notice the change first. A simple timeline helps the team see how it unfolded.

Get urgent care for a first seizure, rapidly worsening confusion, or trouble staying awake.

Sources: Cleveland Clinic: autoimmune encephalitis; NINDS: encephalitis; Neurology Clinical Practice: encephalitis resembling dementia.

Anti-NMDA receptor encephalitis

Anti-NMDA receptor encephalitis is one of the most common forms of autoimmune encephalitis. The immune system makes antibodies against NMDA receptors. These are proteins on the surface of nerve cells.

It mostly affects young people. In a study of 577 patients, 95 percent were younger than 45, and 37 percent were younger than 18. Females outnumbered males about 4 to 1.

In teens and adults, it often starts with psychiatric symptoms. These include agitation, hallucinations, strange beliefs, and poor sleep. Speech problems, memory loss, and odd movements may follow. Later, heart rate, blood pressure, and breathing can become unstable, and alertness can drop. Young children more often start with seizures or abnormal movements.

Some cases are linked to a tumor. In that study, a tumor turned up in 58 percent of women older than 18, usually a benign ovarian tumor called a teratoma. In children younger than 12, tumors were rare, found in 0 to 5 percent. Some cases follow herpes simplex encephalitis. Doctors test for the antibody in both blood and spinal fluid.

Sources: NINDS: encephalitis; Lancet Neurology: clinical approach to diagnosis; Lancet Neurology: anti-NMDA receptor encephalitis outcomes, 577 patients.

What causes autoimmune encephalitis

No one knows why the immune system turns on healthy nerve cells. In many people, no trigger is ever found. In others, a known link shows up.

A tumor can be very small and hard to find. That's why the team may order scans of the chest, belly, or pelvis, even when the person feels fine otherwise. A tumor search isn't proof that cancer is present. Many people don't have one.

Families sometimes look for one event they could have stopped. The evidence rarely points to one. A possible trigger should not be treated as a known cause.

Sources: Cleveland Clinic: autoimmune encephalitis; NINDS: encephalitis; JNNP: diagnosis and acute care.

How doctors diagnose it

Doctors combine the history, the exam, and several tests. Experts first think of possible autoimmune encephalitis when memory loss, confusion, or psychiatric symptoms build over less than 3 months. They also look for one more sign, such as new seizures, swelling on MRI, or spinal fluid changes. Then they rule out other causes.

Antibody results need care. In a study of 107 adults who were wrongly told they had autoimmune encephalitis, half of the errors came from giving a positive blood antibody too much weight. Their real problems included functional disorders, diseases like dementia, and mental health conditions. A negative result has limits too. Some people meet the criteria with no known antibody.

When someone is very ill, specialists may start care before every result is back. They still keep checking for infection and other causes.

Sources: Lancet Neurology: clinical approach to diagnosis; JAMA Neurology: misdiagnosis in adults; Cleveland Clinic: autoimmune encephalitis; JNNP: long-term management.

Recovery and outlook

Cleveland Clinic says autoimmune encephalitis generally responds well to treatment, but recovery can take a long time. In the large anti-NMDA receptor study above, most people responded to immune treatment, and some took up to 18 months to recover. Some people improve within days. Others need weeks or months of care. In that anti-NMDA receptor study, early treatment was linked to a better outcome; it does not show the same for every type.

There is no single life expectancy figure for this illness. The outlook depends on the type, how severe it was, how fast treatment began, and whether a tumor is involved. Serious cases can cause long seizures, coma, or death. Many people do recover, though memory, mood, or stamina may stay affected for a while.

Going home from the hospital is one step, not the finish line. A person may walk and talk but still struggle with planning, focus, or a noisy room. Rehab with physical, speech, and occupational therapy can help. Our treatment guide explains what specialists may consider at each stage. Children have their own needs, covered in our pediatric neuroimmunology guide.

The illness can relapse, especially when an underlying cancer isn't under control. New symptoms after a good stretch need a call to the team. Some forms of brain inflammation overlap with other antibody diseases, such as MOGAD. Our page on what neuroimmunology is explains the wider field.

Sources: Cleveland Clinic: autoimmune encephalitis; NINDS: encephalitis; JNNP: long-term management; JNNP: diagnosis and acute care; Lancet Neurology: anti-NMDA receptor encephalitis outcomes.

Who this page is for

We wrote this for families sitting beside someone with a new diagnosis of autoimmune encephalitis. Patients reading it later, once the fog lifts, may find it useful too, as may nurses and doctors looking for a plain handout. It can't replace the team at the bedside. If what you see at home doesn't match what you're told, say so, and keep asking.