A diagnosis of autoimmune encephalitis (AE) is based on the presence of symptoms and findings on physical examination that are consistent with AE and test results that show inflammation in the brain. In addition, your doctor must make sure that you do not have other more common conditions (such as infections, neurologic diseases and mental health conditions) that may explain your symptoms and test results. Given the large number of conditions that can look like AE, many tests are usually required and making a diagnosis can take many weeks. Criteria now exist to help doctors diagnose AE in adults and children.

The diagnosis of AE is complicated because symptoms can be different in different people and because finding inflammation in the brain often requires multiple tests.  Sometimes, invasive tests, such as a spinal tap or brain biopsy, are needed to confirm a diagnosis of AE or to make sure that the symptoms are not caused by another diagnosis. Also, it can take several weeks to get the results of tests for antibodies to cells in the brain or spinal cord (or anti-neuronal antibodies) that are part of the criteria to make the diagnosis of “definite AE”.

Because of the time it takes to get the results of all tests and also because early treatment for AE helps people get better faster, many experts recommend starting treatment in children or adults who may have AE, or who meet the criteria for “possible AE”.  If test results in a person who was thought to have “possible AE” do not fit with this diagnosis, then they should continue being tested for other conditions that may cause similar symptoms. It is important not to confuse “possible AE” with an actual diagnosis of AE.

Experts have developed criteria for “possible AE”, “definite antibody-positive AE” and “probable antibody-negative AE” in adults and children.

In adults, a diagnosis of “possible AE” is made when all three of the criteria listed below have been met:

1. Subacute onset (rapid progression of symptoms over less than 3 months) of working memory problems (short-term memory loss), altered mental state (such as confusion or decreased ability to interact with other people or surroundings), or psychiatric symptoms (such as hallucinations)
2. At least one of these findings:
   Abnormal findings on the physical examination that suggest a problem in the brain or spinal cord (such as arm or leg weakness, abnormal reflexes or problems with coordination)
   • Seizures that are not explained by a previously known seizure disorder
   • High levels of white blood cells in the spinal fluid
   • MRI abnormalities that fit with AE
3. Reasonable number of test results that show that symptoms are not caused by more common conditions, such as infections or cancers

Graus et al., A clinical approach to diagnosis of autoimmune encephalitis, the Lancet, 2016

Lancaster E., The Diagnosis and Treatment of Autoimmune Encephalitis, JCN, 2016

In children and teenagers, a diagnosis of “possible AE” is made when all three of the criteria listed below have been met:

1. New neurological and/or psychiatric symptoms developing over less than three months in a previously healthy child
2. At least two of these symptoms or findings:

• Reduced ability to interact with other people or surroundings (or slowing on EEG)
• Abnormal findings on the physical examination that suggest a problem in the brain or spinal cord (such as arm or leg weakness, abnormal reflexes or problems with coordination)
• Problems with memory and the process of thinking
• Loss of developmental milestones
• Abnormal movements (except tics)
• Psychiatric symptoms (such as low mood or hallucinations)
• Seizures that are not explained by a previously known seizure disorder or other condition

3. Reasonable number of test results that show that symptoms are not caused by more common conditions, such as infections or cancers

Cellucci et al., Clinical approach to the diagnosis of autoimmune encephalitis in the pediatric patient, Neurology, Neuroimmunology & Neuroinflammation, 2020

AE may be linked to antibodies to  cells in the brain or spinal cord. These antibodies are known as anti-neuronal antibodies. Diagnostic criteria exist for different types of AE where antibodies are present in both children and adults. However, not everyone who is diagnosed with AE will have a detected anti-neuronal antibody. Also, just because a person has an anti-neuronal antibody does not mean they have AE.  Some anti-neuronal antibodies, especially in low levels, can be found in the blood of healthy people.  So, testing for anti-neuronal antibodies may be helpful to diagnose AE, but patient symptoms and other test results are very important for understanding the antibody test results.

To learn more about the science behind antibody testing, watch this webinar:

AE Research Insight – EuroImmun from AE Alliance on Vimeo.

It may be hard for doctors to recognize AE because not all people with AE present in the same way, or have the same symptoms. In addition, many other conditions can present with similar symptoms to AE and some of those conditions are much more common than AE.  It may be especially hard to diagnose AE in younger children who are not able to describe their symptoms well or who may be going through normal behavior changes in childhood.

Therefore, your doctor needs to do a careful history and physical examination, and then decide what tests are needed to confirm a diagnosis of AE and to make sure you do not have one of the other conditions that lead to similar symptoms.  Tests that are often ordered in patients with possible AE include blood work, brain imaging, spinal tap with testing of spinal fluid, and EEG (testing the electrical activity in the brain).

It is important to note that not everyone with the neurological or psychiatric symptoms listed above needs to be tested for AE.

We formed AE Alliance in 2012 in hopes of creating a community of knowledge, resources, and connection. We truly believe that no one should face AE alone. We hope our Welcome Kit will be a helpful resource.

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