Positive temporal sharp waves in preterm infants with and without brain ultrasound lesions
Introduction
Electroencephalographic (EEG) findings in the neonatal period have proved to be fairly reliable indicators of neurologic prognosis for newborn infants, and even to determine subtle encephalopathies (Scher, 1994) before visualization using imaging techniques (Baud et al., 1998). However, the clinical significance of sharp wave transients on neonatal EEG recordings remains uncertain, and they have been reported in asymptomatic neonatal population (Anderson et al., 1985, Clancy and Spitzer, 1985). Positive temporal sharp waves (PTS) are one of the least studied EEG signs, and their real significance is even more controversial. Some authors find PTS to be benign and frequently occurring patterns in asymptomatic preterm newborn infants (Scher et al., 1994a, Scher et al., 1994b). Others have suggested an association between PTS and different pathological EEG signs such as positive rolandic sharp waves (PRS) (Nowack and Janati, 1990, Nowack et al., 1989), or with serious cerebral parenchyma lesions, especially of white matter (Chung and Clancy, 1991, Vecchierini-Blineau et al., 1996). The apparent discrepancy of opinions may be explained, at least in part, by considering the incidence and persistence of PTS at different conceptional ages (CA) in neonates with, and without, independent evidence of neurologic impairment. In addition, there are no studies on the postnatal environmental influence on this EEG pattern. Postnatal life factors can affect certain maturational EEG patterns in preterm infants, which makes many of them present dysmature EEG patterns, including PTS, at more advanced CAs (Scher, 1997a, Scher, 1997b, Scher et al., 1996). Thus, it would seem that there are difficulties in determining what incidence of PTS is characteristic of certain CAs. PTS may arise following local lesions of the temporal lobe which is vulnerable during the traumatic birth period. It is also possible that PTS are triggered by true encephalopathy.
This study prospectively analyzed 97 newborn infants grouped according to gestational age (GA) (ranging from <27 to 36 weeks), which were divided into two groups for statistical purposes, according to the presence or absence of major cerebral lesions (MUL) in the ultrasound. EEG recording was performed in all infants until term CA in order to (1) record and compare PTS incidence per GA. (2) establish the CA at which PTS were most numerous in neonates with and without MUL, (3) correlate these with other background EEG findings and/or other EEG signs associated with poor outcome, and (4) ascertain whether PTS incidence varies with CA because of the influence of extrauterine life.
Section snippets
Patients
We studied a total of 97 preterm infants ranging from <27 to 36 weeks GA, who were hospitalized in our neonatal unit in the period 1993–1998. Infants who failed to survive until 42 weeks CA or who had chromosomal abnormalities and/or multiple congenital malformations were excluded from the present study. GA was calculated from the date of the mother's last menstrual period and confirmed by antenatal ultrasound or, in the case of in vitro fertilization, using the date of insemination. After
Positive temporal sharp waves
Table 2 shows mean PTS per GA group with and without MUL recorded at four different times.
In the first week of postnatal life, PTS waves increased progressively to a peak incidence for those neonates without MUL born at 31–32 weeks GA, then decreased until term GA, with a mean maximum of 4.34 PTS/h (range 1.41–9.27) Multivariate analysis showed a significant relationship between the incidence of PTS and GA (P<0.001). In the second week of postnatal life, there was also a peak incidence for
Discussion
The majority of current reports on sharp waves in preterm infants deal with PRS (Castro et al., 1991, Marret et al., 1997, Okumura et al., 2003), which have been related to lesions in periventricular white matter and poor neurologic prognosis, although their real significance remains somewhat unclear. Currently, there are some studies which refer to PTS, but they are scarce and results are contradictory.
Our data show an insignificant incidence of PTS in the EEG recorded in the first week of
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