Autoimmune epilepsy is a neurological condition where the body’s immune system mistakenly attacks healthy brain cells, leading to recurrent seizures. The electroencephalogram (EEG) is a common diagnostic tool used to assess brain activity. This article explores how EEG is utilized in the context of diagnosing autoimmune epilepsy, while also considering its limitations.
What is Autoimmune Epilepsy?
Autoimmune epilepsy occurs when the body’s immune system mistakenly attacks specific proteins or receptors in the brain, leading to seizures. This involves autoantibodies, proteins designed to protect the body. The International League Against Epilepsy (ILAE) recognized this direct link between immune disorders and seizures in 2017.
Beyond seizures, this condition can manifest with cognitive changes like memory loss and difficulties with thinking, as well as personality and behavioral issues. Common autoantibodies implicated target receptors such as N-methyl-D-aspartate receptor (NMDAR), leucine-rich glioma-inactivated protein 1 (LGI1), and glutamic acid decarboxylase 65 (GAD65). Early diagnosis and treatment are important for managing symptoms.
Understanding the Electroencephalogram (EEG)
An electroencephalogram, or EEG, is a non-invasive medical test that measures the electrical activity of the brain. During the procedure, small metal discs, called electrodes, are placed on the scalp. These electrodes detect the tiny electrical impulses that brain cells use to communicate with each other.
The electrical signals picked up by the electrodes are sent to an EEG machine, which amplifies them and records them as wavy lines on a computer screen. This visual representation, known as brain waves, allows healthcare providers to observe patterns of brain activity. An EEG can help detect abnormal electrical patterns that may indicate neurological conditions.
EEG Patterns in Autoimmune Epilepsy
While an EEG is a valuable tool for evaluating seizure activity, the patterns observed in autoimmune epilepsy are often non-specific. An EEG may show various findings, including focal slowing, generalized slow activity, or epileptiform discharges, which are abnormal electrical spikes or sharp waves. However, these patterns are not unique to autoimmune epilepsy and can be present in other forms of epilepsy or brain dysfunction.
While a specific EEG pattern called “extreme delta brush” has been reported in some cases of anti-NMDAR encephalitis, it is not common. A normal EEG does not rule out autoimmune epilepsy. Many patients with autoimmune epilepsy may have normal EEG findings, especially early in the disease course.
A Holistic Approach to Diagnosis
Given that EEG findings in autoimmune epilepsy can be non-specific, a comprehensive diagnostic approach is necessary. This involves integrating clinical presentation, specialized laboratory tests, and brain imaging. Patient history and symptoms, such as the type and frequency of seizures, cognitive changes, or psychiatric symptoms, provide initial clues.
Specialized blood tests and cerebrospinal fluid (CSF) analysis detect specific autoantibodies targeting brain proteins. However, up to half of patients may not have detectable antibodies. Brain imaging, such as magnetic resonance imaging (MRI), can reveal inflammatory changes or atrophy, though MRI findings can also be normal, especially early on. Positron emission tomography (PET) scans can be more sensitive in detecting focal abnormalities than EEG or MRI. In some cases, a trial of immunotherapy is considered, as a positive response supports an autoimmune etiology.