CHAPTER 6

CLINICAL USE OF AMBULATORY EEG IN PEDIATRICS

ADRIANA ULATE-CAMPOS, MD and TOBIAS LODDENKEMPER, MD

INTRODUCTION

The list of differential diagnoses for paroxysmal events in pediatrics is broad and varies according to the specific age group. For example, in new onset paroxysmal events presenting with eye and arm movements in a healthy infant, clinicians might consider behavioral episodes, stereotypes, spasmus nutans, or epileptic spasms, with considerable differences in terms of management and prognosis between these entities. One of the greatest challenges in pediatrics is the difference in obtaining a seizure history, that is, the inability to interrogate an infant as to what happened. We rely solely on the history provided by the parents and caretakers who are sometimes too nervous or worried to recall all details and the time sequence of the event. In older children and adolescents, alternative diagnoses such as tics, behavioral events, daydreaming, attention deficit disorders, migraine, syncope, cardiac arrhythmias, parasomnias, and seizures are the most frequent alternatives in the differential diagnosis of paroxysmal events (1–3). If after a detailed history and neurological examination the clinician is still uncertain if the event in question is a seizure, then an electroencephalogram (EEG) may be helpful to support the diagnosis and to provide further details regarding the presentation, since an accurate diagnosis is mandatory for an appropriate management.

Inpatient video-EEG monitoring is the gold standard for the diagnosis of epilepsy, but it is expensive due to the high technical and personnel demand required (4,5). The suspected event is rarely captured on the first routine video-EEG monitoring (6). Repeated EEG recordings increase the possibility of capturing epileptiform activity, from 50% during the first record to 92% during the fourth one (7). Therefore, prolonged continuous EEG recordings may also enhance the probability of capturing the suspected event as well as interictal epileptiform discharges. Ambulatory electroencephalography (aEEG) consists of usually continuous monitoring for 24 hours or more, often without video recording (8,9), although technological advances now also facilitate home video-EEG monitoring. Ambulatory EEG implies less disruption of a child’s routine as the patient and family can stay home, and this may also increase the possibility of capturing the desired event. If aEEG is not informative or cannot answer the underlying question, video-EEG or long-term monitoring (LTM) may provide additional diagnostic options (6).

The main indications for aEEG in pediatrics are differentiating epileptic from nonepileptic events, studying sleep-triggered EEG abnormalities, determining seizure/epileptiform discharge frequency, and determination of seizure localization. The referring physician neurologist should provide information regarding the reason for performing the aEEG, a brief description of the events in question, and ideally one or two provisional diagnoses to permit interpretation of the EEG in the setting of the clinical question (4). The clinical information and detailed description of the event may also provide the opportunity to adapt the technical methodology of the study to the patient, for example, adding polygraphic parameters or repeating hyperventilation testing if staring episodes are under investigation (10,11). We strongly recommend to give the family written instructions along with verbal instructions, as well as an event diary log to write down the events. Not every child may be a candidate for an aEEG, and in the following we provide some thoughts on how to select the patients to increase the aEEG utility in this population.

The main advantages of aEEG are recording in the habitual environment of the child, which may allow the child to better tolerate the procedure, and which may permit recording of habitual sleep patterns, as well as overall lower cost than inpatient EEG. Its main disadvantages are the lack of video in most cases, the inability to evaluate the child during the event, the incapacity to reduce antiepileptic drugs (AEDs) as an outpatient due to safety concerns and the inability to interfere and repair electrodes that may develop artifacts during the recording.

TECHNICAL DETAILS OF PEDIATRIC AEEG

EEG electrode placement in pediatric patients requires specially trained and skilled technicians (12). The lab atmosphere must be comfortable, quiet, and child-friendly, with decoration and toys suitable for children (12). At least one parent or caregiver should be present in the lab during the electrode placement to calm the child and to explain what is being done (13), and in behaviorally challenging patients, a child life specialist can be of huge help to prepare and perform for the electrode placement and recording.

Newer systems according to the 10–20 standard of electrode placement have overcome the problem that was noted during the early four-to eight-channel cassettes, in which highly focal seizures or asymmetries could go undetected, and artifacts may have been more easily confused with epileptiform abnormalities (14–16). Electrode placement according to the standard 10–20 system is now considered standard of care (2,6,16–18). In the neonate, the system has to be modified, with at least eight electrodes positioned according to the 10–20 system, but most neonates tolerate a 10- to 20-electrode placement of 16 electrodes well (10). Electrodes could be attached to the scalp with collodion, fixed onto a head cap or inserted into a soft cap to increase tolerability (10). If electrodes are attached, the head may be wrapped to lessen the chance of electrode misplacement, especially in active kids (4). Neonates and infants require close care of the skin, since the neonatal scalp is more fragile; collodion may be changed for another paste that is easier to remove and has a lower incidence of scalp lesions and scalp irritation (10,13).

Extreme cases of energetic children may need sedation for electrode placement and closer parental supervision during the recording because electrodes could be pulled, bent, or unplugged (17). These situations can often be overcome without sedation by preparation with a child life specialist, and based on this strategy, we did not require sedation in any of our pediatric cases in past years. In order to prevent scalp lesions and improve the quality of recordings, we may include scheduling of daily visits to the EEG laboratory to check, replace, or gel electrodes as needed (18), and to recognize skin breakdown early. But this may not be feasible if the family lives far away from the EEG laboratory, in which case at times caregivers may be trained to gel electrodes with electrode paste (18).

Additional channels for electromyography (EMG), oximetry, and EKG may enhance the system detection capacity in selected cases (18). Some patients may benefit from eye or chin leads, or a respiratory belt and oximetry, if sleep patterns and respiratory patterns, that is, apneas, are of importance. For example, an EKG channel provides a lot of information when studying episodes of “fainting” or syncope that could potentially have cardiac origin. EMG may assist with the differentiation of abnormal movements and may also provide improved EEG time relationships and correlation for motor seizures, such as myoclonus, epileptic spasms, and tonic seizure, in particular when no video is available. At least an EKG channel is recommended in pediatric aEEG, and the combination of other channels may be adapted according to the episode in question as described by the ordering clinician.

Since records are now usually electronic, the montage, amplitude, display speed, and filters may be modified as needed when the aEEG is evaluated by the neurologist to obtain most information from the recording. Another option is computer assisted outpatient EEG which may improve the seizure detection in aEEGs (2). But visual analysis by a knowledgeable person remains the gold standard (35).

Activation procedures may be performed immediately after EEG lead placement, during a baseline EEG recording in the EEG laboratory. This will also permit a quick visualization of the tracings by the technician, including tentative lead repairs and including impedance checks (2,12). If there is a clear asymmetry, the distance between the involved electrodes could be checked and replaced, if needed. This baseline recording usually includes eye opening and closure, as well as activation procedures such as hyperventilation and intermittent light stimulation and as appropriate mental stimulation (ie, animal naming or counting) to enhance the information provided by the aEEG. Hyperventilation can at times be performed around 2 to 3 years of age. Most children with normal development around the age of 4 to 5 may be able to comply with blowing a pinwheel, but in younger children sobbing or crying may have a similar hyperventilatory effect (6,12).

Video recordings are often useful since viewing the semiology of the event makes it easier to interpret the concomitant electrical record. In a cohort of adult and pediatric patients, home video aided in the interpretation of the aEEG in approximately one third of cases (19). In cases in which aEEG has video, this compromises mobility, since the child either may move out of the camera range and might not be visible during the suspected event, or caregivers must constantly monitor and tentatively reposition the camera (18).

Most available aEEG systems can store data up to 72 hours at 256 Hertz for 26 to 32 channels (18). Ambulatory EEG equipment often requires a battery change or charge every 24 hours. If the family is able to visit the lab for an electrode check every 24 hours, then batteries may also be changed by the technologist.

RECOMMENDATIONS FOR THE FAMILY

Up to 98% of recordings in pediatrics are technically satisfactory (2), but to achieve this, counseling of the families, that is, by means of a counseling session, a sheet, a video, or a combination of these techniques to train caregivers regarding instructions, is crucial. An example is provided in Table 6.1. On the day of the scheduled appointment, the child should have the regular meals and receive the usual medications. For the equipment to be placed, the child should come with clean hair and without any ointments or creams in the area of electrode placement, to allow the electrodes to adhere properly. Shirts with front buttons are more practical to avoid tearing the electrodes when changing a garment over the child’s head. The child may attend school, but this must be planned ahead with the school staff; teacher and student counseling may need to be provided. We usually recommend that the child is supervised by an adult at all times to watch the equipment, but also to push the button and write down events in the log (Table 6.1).

We suggest that the family maintains the usual daily routine including medications, eating, and habitual sleeping hours. Vigorous physical activity should be limited, in particular contact sports and swimming (Figures 6.1 and 6.2) (2). The child is also asked to limit baths and showers to prevent interference with equipment function and recording quality (18). Snacking and gum chewing should ideally not be excessive during the recording to reduce chewing artifact (Figure 6.3). Brushing the hair and scratching the head should be minimized if possible. The family is also asked to try to keep electrical equipment such as cell phones, computers, and other portable devices away from the headbox. Depending on battery life, the family is also instructed to change the battery regularly, with our current system ideally every 24 hours to permit functioning at different temperatures and for the duration of prolonged aEEGs. Caregivers are asked to push the event button every time an event is witnessed. It is crucial for families to keep a diary of events, with a detailed description, the time of day, and the duration of the event. In the experience of Foley et al, up to 30% of aEEG studies are returned without a written diary or accurate time log, which may reduce the yield of the study (6).

TABLE 6.1  Recommendations for Caregivers: Ambulatory Electroencephalogram

FIGURE 6.1 Rocking artifact in an autistic patient.

FIGURE 6.2 Movement artifact in an autistic patient.

FIGURE 6.3 Chewing artifact.

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