Electroencephalography (EEG) is a non-invasive medical test that measures the brain’s spontaneous electrical activity. This procedure uses small sensors placed on the scalp to detect the tiny electrical signals generated by brain cells, providing a graphical record of brain waves. Migraines are a common neurological disorder characterized by recurrent, moderate to severe headaches, often accompanied by nausea and sensitivity to light or sound. While diagnosis is typically based on clinical history, an EEG may be used in specific, limited circumstances when investigating severe or unusual headache presentations.
Understanding the EEG Procedure
The EEG procedure is painless and generally takes about one to two hours, including preparation time. Patients are instructed to wash their hair with shampoo but avoid using conditioners, gels, or oils, as a clean scalp ensures the electrodes adhere properly. It is also recommended to avoid consuming caffeine for at least eight hours prior to the test, since stimulants can alter the brain’s natural electrical patterns.
During the recording, a trained technician measures the head to determine the precise placement of the small, metal disc electrodes. Usually, 16 to 25 electrodes are affixed to the scalp using a conductive paste or cream. The patient is asked to relax in a reclining chair or lie on a bed, remaining still while the machine records the electrical signals.
To provoke certain brainwave patterns and assess the brain’s responsiveness, the technician may introduce activation procedures. These often include asking the patient to breathe deeply and rapidly (hyperventilation) for a few minutes. Another common technique is photic stimulation, where a strobe light flashes at different speeds. The machine translates the electrical activity into wavy lines that a neurologist will later analyze.
The Role of EEG in Differential Headache Diagnosis
An EEG is not a standard tool for confirming a migraine diagnosis, as the condition is primarily diagnosed through a detailed review of the patient’s symptoms and medical history. Its main purpose in the context of headaches is differential diagnosis—to rule out other serious neurological conditions that can mimic migraine symptoms. A neurologist may order the test when the clinical presentation is atypical or suggests an underlying structural or functional problem.
The test becomes relevant when a patient’s headaches are accompanied by specific concerning features. These include unusual auras, episodes of loss of consciousness, or signs of confusion. Such symptoms may raise suspicion for seizure disorders, which frequently co-occur with migraines. The EEG can help distinguish between a complex migraine aura and a partial epileptic seizure, which can present with similar visual or sensory disturbances.
By examining the brain’s electrical patterns, the EEG helps to exclude causes of secondary headaches, which are those caused by another medical condition. These secondary causes can include brain tumors, inflammatory conditions, or vascular lesions, though neuroimaging is typically the primary method for ruling out structural issues. If a patient’s headache does not respond to standard migraine treatments, or if the symptoms are progressively worsening, an EEG provides an objective measure to investigate potential alternative diagnoses.
Interpreting EEG Results in Headache Patients
When a neurologist reviews the EEG tracing for a headache patient, the results are usually normal, which supports the diagnosis of a primary headache disorder like migraine. The absence of significant, consistent abnormal electrical activity helps assure the clinician that the chronic pain is not caused by a serious underlying disorder. This finding is clinically important for both diagnosis and patient reassurance.
An abnormal result suggests a deviation from the expected brain wave patterns and points toward a different neurological condition. The most significant abnormality is the presence of epileptiform discharges, which appear as sharp waves or spikes in the tracing. These patterns strongly suggest a diagnosis of epilepsy or a predisposition to seizures, even if the patient has not experienced a recognized seizure event.
Some studies have noted that patients with migraines, particularly those with aura, may show a higher frequency of minor EEG abnormalities, such as generalized or focal slowing of brain wave activity. While these findings do not confirm a migraine diagnosis, they suggest a degree of underlying neuronal excitability or dysfunction consistent with the condition’s pathophysiology. Ultimately, the EEG serves as a specialized tool to identify or exclude seizure activity and other electrical abnormalities, guiding the next steps in a patient’s diagnostic and treatment plan.