An electroencephalogram (EEG) is a medical test that measures the electrical activity produced by the brain. This activity is recorded using small metal discs, or electrodes, placed on the scalp. A standard, routine EEG typically lasts only about 20 to 40 minutes, which is often insufficient to capture sporadic neurological events. Long-term monitoring (LTM) expands this recording time significantly, often spanning several days or even a week. This extended duration is necessary to capture electrical patterns that occur infrequently or only during specific states, such as sleep or during a characteristic event.
Diagnostic Applications of Extended EEG
Because many neurological symptoms occur randomly, continuous monitoring greatly increases the probability of capturing a symptomatic event. Capturing the event allows physicians to correlate the patient’s physical experience with the underlying electrical activity in the brain. This process is essential for differentiating between true epileptic seizures and non-epileptic events, such as psychogenic non-epileptic seizures (PNES) or syncope. Accurate diagnosis is a priority because the treatment approach for these conditions differs significantly.
Extended monitoring also helps physicians classify the type of seizure and determine its precise origin within the brain. Identifying the exact location of abnormal electrical discharge is important for treatment planning, especially when considering surgical options. LTM is also used to assess how well a patient is responding to current anti-seizure medication. The extended recording provides a baseline frequency and severity of electrical abnormalities, allowing doctors to adjust drug dosages precisely.
Setting Up the Monitoring Session
The initial setup for long-term monitoring begins with a trained technologist preparing the scalp. The skin is gently scrubbed with a mild cleanser to remove oils and dead skin cells, ensuring optimal electrical conductivity. Multiple small electrodes, typically 21 or more, are then affixed to the scalp using a strong, specialized conductive paste or collodion glue. Each electrode is placed according to the international 10-20 system and connected by wires to a small, portable recording device.
LTM can be conducted in two ways. In an ambulatory setup, often done at home, the recording device is worn in a small pack, allowing the patient to move around. An inpatient setup, conducted in a hospital unit, often involves a fixed headbox connected to a central monitoring station. Monitoring duration commonly ranges from 24 hours up to seven days, depending on the frequency of the patient’s events.
Navigating the Monitoring Period
Patients must make lifestyle adjustments during long-term monitoring. Activities involving water, such as showering or swimming, must be avoided because the electrodes must remain securely fastened to the scalp. Patients are advised to wear button-down or zip-up shirts to make dressing easier without pulling on the electrode wires.
The patient must carry or wear the recording box, which must remain close to the head at all times. In hospital settings, movement is often restricted, especially if the monitoring includes Video-EEG (VEEG). VEEG uses a camera to continuously record the patient’s physical behavior, enabling electroclinical correlation.
This video component allows specialists to precisely match the patient’s physical symptoms with the corresponding brain wave changes. The patient or a caregiver uses an “event button” on the recording device whenever a symptom occurs, placing a digital timestamp directly onto the EEG recording. They are also instructed to keep a detailed log, noting the exact time the button was pushed and a verbal description of the observed symptoms. This log helps the monitoring staff interpret the timestamped data accurately.
Analysis and Findings
Once monitoring is complete, the raw data is transferred from the recording device. Long-term recordings generate hundreds of hours of continuous brain wave activity, which is first processed by specialized computer software. Trained technicians filter out artifacts, which are non-brain electrical signals caused by muscle movement, eye blinks, or static electricity.
A clinical neurophysiologist or neurologist systematically reviews the processed EEG data, focusing on segments marked by the patient’s event button. They determine if the recorded neurological event is associated with abnormal electrical waveforms, such as spikes or sharp waves. This correlation between logged symptoms and electrical data is essential for diagnosis.
Because of the amount of data collected and the meticulous manual review required, receiving the final comprehensive report can take several days or weeks. The physician synthesizes the findings to produce a written report detailing the presence or absence of epileptiform activity and its correlation with the patient’s clinical symptoms.