- Paediatric EEG
- Normal Awake
Introduction
- Drowsy patterns
- Burst Drowsy Patterns
- V Waves
- Spindles
- V Waves and Spindles
- Positive Occipital Sharp Transients of Sleep (POSTS)
- Occipital Sharply Contoured Waves and Delta
- 14 and 6 per Second Positive Spikes
- Arousal Sequence
Moreover, infants and young children tend to become drowsy during the recording, and the electrographic alterations with drowsiness are greater than those with adults. These factors create wider limits of normality than might be expected in adults. In addition, the superimposition of two or more waveforms often creates sharply contoured waves that can be mistaken for spikes. Fortunately, most of the clinically significant EEG abnormalities in children are morphologically well defined. However, to identify abnormalities in children's EEGs with confidence, it is first necessary to sharpen one's concept of normal features and their variations.
For each state of alertness (wakefulness, drowsiness, sleep, and arousal), the electroencephalographer interpreting a child's recording should ask the following questions:
- The electroencephalograms (EEGs) of infants and children are normally characterized by a greater mixture of waveforms and frequencies than is found in adults.
- The relative predominance of these wave types varies with age.
- There may be considerable intersubject variability, possibly because of differences in maturation.
- Several waveforms, such as the initial response to hyperventilation and posterior slow rhythms of youth, may be normally asymmetrical.
For adults, similar criteria apply:
- Is the electrical maturation adequate?
- Are there any marked nonartifactual asymmetries beyond those normally accepted for certain waveforms?
- Are there any spikes?
- Is there any excessive focal or diffuse delta activity?
Children Awake Recordings Background Activity
Hans Berger was the first to recognize that the frequency of background activity in childhood increases with age, (Gloor, 1969). Studies by Dreyfus-Brisac (1975), Hagne et al. (1973), Pampiglione (1972), Petersen and Eeg-Olofsson (1971), and Samson-Dollfus and Goldberg (1979) have provided the frequency milestones outlined below.
There is no discernible dominant occipital activity until the age of 3 months, at which time a rhythm of 3 to 4 Hz can be seen. Its frequency increases to approximately
- Are normal phenomena present: alpha, mu, theta, V waves, spindles?
- Are such features symmetrical or almost so?
- Are states (wakefulness, drowsiness, sleep, and arousal) easy to identify and do they contain normal features?
- Are abnormal spikes present?
- Is there focal or diffuse excess delta activity for state?
Background activity can be appreciated best by passive eye closure, as the background can be attenuated by eye opening as early as age 3 months. Gentle passive closure of the eyes can be maintained for a few seconds. A low frequency filter (LFF) of 1 Hz might be helpful to decrease the quantity of movement artifact at such times.
The occipital rhythm may also be seen during crying, as this is often associated with eye closure. In estimating the background frequency, it is important to assure that the patient is not drowsy. Drowsiness should be suspected if there is less than the usual quantity of muscle artifact for age. During drowsiness, the background activity can be 1 to 2 Hz less than that for wakefulness; in children, this can persist for prolonged periods after sleep, even when the child appears alert.
Thus, passive eye closure should be performed at times when complete alertness is assured. There is moderate intersubject variability of background amplitude. The following data will help to assess whether abnormal amplitudes exist, particularly if they are too low, suggesting a focal or diffuse paucity of cortical activity.
Recording with the eyes open, Hagne (1968) found an amplitude of 10 to 20 µV in the first months of life, increasing to 20 to 40 µV at 6 to 12 months. Using the passive-eye-closure technique, Pampiglione (1972) found an amplitude of 50 to 100 µV at age 3 months, increasing to 100 to 200 µV at age 9 months.
During passive eye closure, we have found considerable wave-to-wave amplitude variability in the first year of life, usually from 30 to 100 µV, with occasional waves reaching 200 µV in the latter part of the first year. Pampiglione (1972) reported amplitudes of 50 to 80 µV at age 2 years. The alpha amplitude in the study of Petersen and Eeg-Olofsson (1971) increased to a maximum at 6 to 9 years and then declined. In their study, the average alpha amplitude for children between 3 and 15 years was 56 µV, the amplitude of 90% of their children falling between 30 and 100 µV.
The alpha exceeded 100 µV in 9% and remained between 20 and 30 µV in 1%. All of the latter were 12 to 15 years of age. None of the normal subjects showed a background activity less than 20 µV. Most studies (Corbin & Bickford, 1955; Cornil & Gastaut, 1947) report that alpha activity tends to be higher on the right side. Petersen and Eeg-Olofsson (1971) found alpha-amplitude asymmetries in nearly all children, usually higher on the right. Five percent of their normal population showed an amplitude asymmetry exceeding 20% on the higher side.
They found no relationship between alpha asymmetry and handedness. Posterior Slow Waves and Lambda The alpha rhythm in youth normally and commonly is interrupted by slower rhythms that occasionally combine with the alpha rhythm to create complex and often sharply contoured waveforms. These waveforms appear in the occipital, parietal, and posterior temporal regions. They attenuate with eye opening and may be augmented by hyperventilation. Their prominence may shift from side to side.
Polyphasic Potentials
Polyphasic potentials consist of 250 to 500 ms, medium to high-voltage waves occurring singly or repeating at 2 to 4 Hz. The main body of these waves is usually electropositive. It is often preceded and followed by an alpha wave whose negative-going deflection is greater than usual. Low-amplitude alpha waves may be superimposed upon this 250 to 500 ms potential. These features together create the polyphasic morphology of the phenomenon. Occasionally the accentuated alpha component, together with the after-coming slow wave, can resemble superficially a spike–wave complex, which it is not.
Some polyphasic potentials were found in nearly all of the normal controls reported by Petersen and Eeg-Olofsson (1971), although these potentials were present in only minimal amounts in 30%. The quantity increases gradually during the first decade of life, to peak from ages 9 years to the early teens. This increase in polyphasic potentials may give the false impression of deterioration in sequential EEGs carried out during this age period. Their prominence may be greater at the start of a recording than later.
Polyphasic potentials may be asymmetrical; if so, they are usually of higher voltage on the right. However, the asymmetry should not persistently exceed 50%.
Slow Posterior Rhythm or Posterior Rhythmic Waves
Slow posterior rhythm (SPR) is sinusoidal, of low to medium voltage, 2.5 to 4.5 Hz, and may appear in brief sequences or prolonged runs. Less commonly, it may appear in medium- to high-voltage bursts. This rhythm was originally thought to be associated exclusively with absence attacks, but Petersen and Eeg-Olofsson (1971) found this rhythm in 25% of their normal population. It occurred more commonly in younger children; its incidence increased from 1 year of age to a maximum at 5 to 7 years.
The SPR amplitude was 50 to 100 µV in 90% of the children, but it exceeded 100 µV in 10%. In 25% of the children, the SPR episodes lasted 3 s or more. In 16% of the children, this rhythm occupied more than 10% of the posterior activity; in approximately half, it constituted 2% to 10%. The distinction between this normal phenomenon and a series of rhythmic waves that are actually abortive spike waves is not always clear. Rarely, such rhythmic waves can merge into clearly defined posteriorly situated spike waves; this may occur under the influence of hyperventilation. Thus, if the patient is referred for a question of absence attacks and the SPR is seen, a second attempt at hyperventilation may be indicated.
However, unless clear spike waves are seen, no statement ascribing epileptogenic significance to such waves should be made.
Slow Alpha Variant
This waveform appears to be created by the partial fusion of two alpha waves, creating a notched waveform at half the alpha frequency, as described by Goodwin (1947). Unlike the first two posterior slow waves, this is not peculiar to children. Petersen and Eeg-Olofsson (1971) found such waves in 3.5% of their normal childhood population.
Lambda Waves
Lambda waves are sharply contoured occipital transients evoked by saccadic eye movements scanning a well-illuminated picture or complex design.
The most constant and prominent phase is surface positive, whose duration is 75 to 150 ms; a subsequent 200 to 250 ms negative phase also may occur (Kooi et al., 1978). In early childhood, blinking or other eye movements may evoke sharply contoured occipital transients whose major phase is electronegative; this lasts 200 to 400 ms and may attain 100 to 200 µV. It may be preceded and followed by lower-voltage electropositive phases (Westmoreland & Sharbrough, 1975).
This phenomenon occurs mainly from age 6 months to 10 years, attaining a maximum incidence and prominence between 2 and 3 years of age. Their association with scanning well-illuminated, interesting objects links these transients with lambda waves. Lambda waves may attain higher amplitudes in children, giving them a spike-like configuration. Their occasional asymmetry in normal children furthers this resemblance to occipital spikes. Darkening the room, staring at a blank card, and eye closure will eliminate lambda waves.
Theta and Delta Activity
Varying amounts of diffuse theta activity are seen in the awake records of all pediatric age groups. Theta is seen as a central rhythm at age 3 weeks. The total quantity of theta increases sharply throughout the first years of life, reaches a peak at approximately age 5 to 6 years, and declines thereafter (Hagne, 1968; Corbin & Bickford, 1955). However, as noted in the previous section on posterior slow waves, theta appearing in the posterior head regions may be more prominent at later ages. With the eyes closed or open, theta is the dominant diffuse activity in recordings in the 2- to 5-year-old age group. With eyes closed, its total quantity is approximately equal to that of alpha activity at ages 5 to 6 years, after which alpha very gradually becomes more predominant. However, the relative proportion of alpha and theta varies considerably among normal children. It is often more prominent over the left hemisphere than the right at all ages.
The area of theta distribution is widespread in younger children and tends to be confined to temporal and occipital regions in older children. Despite the aforementioned variations, there is little change in theta frequency with age. Despite its normal prevalence, or perhaps because of it, cerebral disease very rarely manifests itself as focal or diffuse excess theta activity. The rare exceptions are (a) diffuse bursts of 3 to 4 Hz waves not related to drowsiness, which may herald the later appearance of generalized spike–wave discharges, and (b) an awake tracing containing only theta activity in chronic, static, severe encephalopathies. In older children and adolescents as in adults, focal excess theta may be an abnormality. However, its predominance in one region should be consistent before definite clinical significance is ascribed.
Therefore, the electroencephalographer reading the child's EEG does not have to worry about the quantity of diffuse theta activity as long as there is some variability in its quantity and other normal frequencies are present. Perhaps the major reason why the quantity of diffuse or even regionally accentuated theta is difficult to correlate with disease processes is the considerable intersubject variability in theta quantity in all age groups (Petersen & Eeg-Olofsson, 1971; Samson-Dollfus & Goldberg, 1979).
Although frequency analysis indicates that delta activity dominates during the entire first year of life (Hagne et al., 1973; Pond, 1963), delta and theta appear approximately equally prominent to visual inspection in the first year. The absolute quantity of delta activity increases throughout the first year (Hagne, 1968) and actually continues to do so until the fifth year (Corbin & Bickford, 1955). However, this increase is less than that for theta; for this reason, theta activity becomes more prominent as the first year progresses and is the dominant diffuse awake activity in the 2- to 5-year-old age group. Delta activity is commonly diffuse in early childhood but may be transiently asymmetrical, the side of maximum expression shifting over the course of the EEG recording.
Therefore, it is important to examine long stretches of the recording before concluding that delta clearly predominates in one region. Small amounts of diffuse delta activity can normally be identified in older age groups, even into adolescence.
Beta Activity
Petersen and Eeg-Olofsson (1971) found beta activity at 10 to 20 µV in various quantities in all awake recordings of their 743 unmedicated normal children. Amplitudes above 20 µV appeared in only 1%. Other principles concerning beta activity in awake recordings for adults also apply to children.
- Normal Awake