blood test being prepared with lab worker

A number of tests can be done to look for – and in some cases confirm – an autoimmune cause of epilepsy. Available tests have improved significantly over the past decade, as we know about more and more antibodies that can cause seizures.

However, currently available tests have their limits and may not be able to find an abnormality in every suspected case of autoimmune epilepsy. Positive tests may not necessarily mean the main cause of the epilepsy is autoimmune.

Autoimmune test results are only meaningful when viewed with a person’s history and other test results.

Antibody Testing

The main diagnostic test for autoimmune epilepsy is a panel of antibodies, which can be found in blood or spinal fluid. Many laboratories now offer these panels in the U.S. and abroad, both in research and in commercial laboratories.

Testing can identify two main types of antibodies.

Antibodies that Target Proteins Inside the Cell

These antibodies can often exist in people who have a cancer. They are often a byproduct of the body’s immune attack on the cancer. If one of these antibodies is found in the blood or spinal fluid and there is no history of cancer, then further tests to rule out cancer are often necessary.

Antibodies that Target Proteins on the Surface of the Cell

These antibodies do not always happen in people who have a cancer, although with certain types of antibodies, specific tumors can happen. For example, NMDA-receptor antibodies, which target the cell surface, can happen in women with ovarian teratomas (cysts).

Antibodies can be tested for with different laboratory assays.

  • A general first screen is often done through an indirect immunofluorescence assay. In this test, tissue sections with fluorescent tags are stained against the person's sample. If a particular pattern of staining is seen, further tests can be done to find out which antibody is present.
  • Individual cells can be made to show a particular protein to find out if the person's spinal fluid serum recognizes that protein. This is called a cell-based assay.
  • In other cases, a Western blot is done to detect individual patterns of antibodies by their size. This is done by inserting the person's serum or spinal fluid onto a gel membrane.

Antibody panels vary from laboratory to laboratory. Different lists of antibodies are tested for depending on the type of panel ordered.

It is important to ensure the laboratory test looks for the appropriate antibodies.

Generally, laboratories repeat testing when an antibody is found or suspected to confirm its presence. This lowers the risk of false positive tests, which can cause anxiety and unnecessary treatment.

Lumbar Puncture

Some people with autoimmune epilepsy may not have any antibodies in the blood and only have them in the spinal fluid. This often occurs later in the disease, when immune cells in the brain start producing antibodies.

A lumbar puncture, also known as spinal tap, can then be done to collect spinal fluid.

  • During a lumbar puncture, a needle is inserted in the lower back, between vertebrae, to collect spinal fluid.
  • The procedure is similar to the epidural performed in women giving birth to relieve pain, except the needle is then moved forward to collect spinal fluid.
  • This procedure is done with local freezing to minimize discomfort.
  • The needle is inserted several levels below the spinal cord, so there is no risk of paralysis.
  • A headache after a lumbar puncture is common and often improves with rest and caffeine.
    • Rarely, the headache may not improve and may require a procedure called an "epidural blood patch."
    • To "patch" a leak of spinal fluid, the person's own blood is injected in the area where the needle was inserted during the lumbar puncture.
  • Spinal fluid is sent for routine analysis, including white and red blood cell counts, glucose, and protein.
  • A test for oligoclonal bands can also be done to see if the brain is making immunoglobulins, which are proteins produced by the immune system.
  • Finally, spinal fluid can be sent for other types of tests to ensure there are no other causes of seizures, such as infections and cancer.

MRI and EEG

MRI (magnetic resonance imaging) and EEG (electroencephalogram) are routinely done in any person with epilepsy and may also provide evidence for autoimmune epilepsy.

  • In some cases of autoimmune epilepsy, there may be bright or swollen areas on an MRI, particularly in the temporal lobes. Other swollen or bright areas can occur in the rest of the brain.
  • In other cases of autoimmune epilepsy, an MRI may be completely normal.
  • An MRI is important to rule out other causes of epilepsy such as stroke, tumor, or brain malformation.

An EEG may show evidence of epileptic activity and can be useful to show which parts of the brain are predisposed to having seizures. Specific EEG findings in autoimmune epilepsy are rare but can happen in some people with severe seizures and disease, requiring them to be in the hospital.

Other Tests

Imaging tests may need to be done to rule out an underlying cancer, as this can sometimes trigger autoimmune epilepsy. This is often done first with a CT (computed tomography) scan of the chest, abdomen and pelvis, as well as an ultrasound of the ovaries in women and testicles in men.

If a CT scan or ultrasound does not show a cancer, a whole-body positron emission tomography (PET) scan may be done.

  • For this test, the person is injected with a tracer taken up by cells in the body that use high amounts of glucose.
  • Since cancers often are very active and require glucose, this test can detect small cancers that may be missed on CT scans.
  • A PET scan of the brain can also look for areas that use up a lot of glucose, which can be seen in autoimmune epilepsy. In some cases, finding these active brain areas may increase the likelihood of autoimmune epilepsy.

In some people with antibodies associated with cancers, imaging tests for cancers may be initially negative. In those cases, CT or PET scans may need to be repeated after a few months.

Authored By: 
Claude Steriade MD, CM
Authored Date: 
02/2020
Reviewed By: 
Jeffrey W. Britton MD
Andres M. Kanner MD
on: 
Saturday, February 15, 2020