An Electroencephalogram (EEG) measures the electrical activity of the brain, recording signals from brain cells. A standard EEG typically captures brain activity over a short period, often 20 to 40 minutes, within a clinical setting. An ambulatory EEG (aEEG) extends this monitoring by allowing continuous recording outside a hospital or clinic. This portable solution enables individuals to carry out their normal daily routines, increasing the likelihood of capturing intermittent or rare brain wave abnormalities missed during a shorter, in-office EEG.
How an Ambulatory EEG Works
The ambulatory EEG setup involves placing small, flat metal discs, called electrodes, onto specific areas of the scalp. These electrodes are typically secured with a special adhesive or glue to ensure they remain in place for the duration of the recording. In some instances, an elastic cap fitted with electrodes may be used instead. The application process for the electrodes and setup of the equipment usually takes about an hour.
The electrodes are connected by thin wires to a small, portable recording device, which is often worn on a belt or carried in a small bag. This device continuously measures and amplifies the brain’s electrical signals, converting them into digital data. The recorder stores this information, which can then be analyzed by medical professionals. While wearing the equipment, individuals are encouraged to maintain their usual daily activities, including sleeping, working, and light exercise.
A crucial part of the ambulatory EEG process is keeping a detailed diary or log of activities and any symptoms experienced. This log should include the date and time of events, such as eating, taking medications, sleeping, or any unusual sensations or spells. Most recording devices also have an “event” button that the patient, or a caregiver, can press to mark the exact time an event occurs. This timestamp allows neurologists to correlate specific symptoms or behaviors with the recorded brain activity. The continuous monitoring typically lasts for 24 to 72 hours, though it can extend for several days depending on the physician’s needs.
What Conditions It Helps Diagnose
An ambulatory EEG is particularly useful for diagnosing conditions where abnormal brain activity is not constant but occurs intermittently. Its extended recording capability increases the chances of capturing these transient events that might be missed during a brief, routine EEG. This makes it a valuable tool in clarifying diagnoses where symptoms are sporadic.
The test is frequently used to diagnose and classify seizure disorders, such as epilepsy. It can help identify the type and frequency of seizures, even those without obvious external symptoms, which are known as silent seizures. For individuals whose seizures persist despite medication, an ambulatory EEG can provide insights into the specific type of epileptic seizure, helping to refine treatment plans. It can also help differentiate between epileptic seizures and non-epileptic events, which may have different underlying causes.
Beyond seizure disorders, an ambulatory EEG can also assist in investigating unexplained spells, fainting episodes, or periods of altered consciousness. By recording brain activity during these events, it can help determine if they have a neurological origin. Certain sleep disorders or behavioral changes suspected to have a neurological basis may also be evaluated using this extended monitoring.
Preparing For and During the Test
Proper preparation for an ambulatory EEG helps ensure clear and accurate recordings. Patients are typically advised to wash their hair thoroughly the night before or the morning of the test, avoiding the use of conditioners, hair sprays, gels, or other styling products. These products can interfere with the electrodes’ ability to adhere to the scalp and conduct signals effectively. If hair extensions or braids are present, they may need to be removed prior to the appointment.
During the setup, a technician will measure the head to mark precise locations for electrode placement. A gritty cream might be used to gently abrade the scalp at these spots, improving conductivity. Once the electrodes are attached with adhesive, they are usually covered with gauze and secured with a net wrap or cap to protect them. Patients should wear comfortable clothing, such as a button-down or zip-front shirt, as pulling clothes over the head after electrode placement can dislodge them.
While wearing the ambulatory EEG equipment, it is important to be mindful of the device and electrodes. The equipment should be kept completely dry, meaning patients cannot shower, bathe, or swim until the electrodes are removed. Strenuous activities that cause excessive sweating should be avoided, as sweat can loosen the electrode adhesive. Patients should also refrain from touching or scratching their scalp near the electrodes, as this can create artifacts in the recording. Limiting cell phone usage and avoiding Bluetooth devices can also help prevent electrical interference with the recording. Continuing to accurately log all activities and any symptoms in the patient diary remains important throughout the monitoring period.
Understanding Your Results
After the prescribed recording period, the ambulatory EEG equipment must be returned to the clinic or hospital. A technician will then carefully remove the electrodes and clean any adhesive residue from the scalp. The recorded data is then downloaded from the portable device for analysis.
A neurologist or a trained technician specializing in EEG interpretation will review the extensive brain activity data. This analysis involves identifying specific brainwave patterns, including any abnormal discharges or changes that correlate with events noted in the patient’s diary. The interpretation can be complex, as brainwave patterns change based on states like wakefulness and sleep, and even subtle movements can create signals that need to be distinguished from brain activity.
Once the analysis is complete, the results are sent to the healthcare provider who ordered the test. The provider will then discuss the findings with the patient, interpreting them within the context of their medical history, symptoms, and other diagnostic information. This comprehensive approach helps guide diagnosis, determine the most appropriate treatment plan, and inform any necessary follow-up care.