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Flash visual evoked potentials and early visual development in infants born to drug misusing mothers

McGlone, Laura (2012) Flash visual evoked potentials and early visual development in infants born to drug misusing mothers. MD thesis, University of Glasgow.

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Abstract

Background / Aims: Maternal drug misuse in pregnancy is a significant clinical and public health problem. Consequences for the newborn infant include prematurity, intrauterine growth restriction (IUGR) and neonatal abstinence syndrome (NAS). There is increasing evidence that maternal drug misuse in pregnancy may have longer term adverse effects on infant visual and neurodevelopmental outcome. Most of the evidence regarding visual outcomes in particular derives from small uncontrolled studies with a lack of adequately powered, controlled studies to date. The visual evoked potential (VEP) can be used to assess the integrity and maturity of the infant visual pathway and both visual and neurodevelopmental abnormalities can be predicted by abnormal VEPs in infancy. Drug misuse is also associated with alteration of the VEP in adults and in animal models. Many drugs used in pregnancy can cross the placenta and enter the fetal circulation, including illicit drugs and prescribed methadone, which is the currently recommended treatment for pregnant opiate-dependent women. Hitherto few studies have investigated the effects of maternal drug misuse upon the newborn infant VEP. This study investigates in detail the effects of prescribed methadone and additional illicit drug use in pregnancy upon the infant VEP recorded at birth and at six months of age, and explores any association with NAS. The range and incidence of visual and neurodevelopmental abnormalities at six months of age is described, and how these relate to a history of NAS and the pattern of in utero drug exposure is explored. Pilot work: Pilot work demonstrated the feasibility of recording neonatal flash VEPs in a small group of infants exposed to methadone in utero, and showed that drug exposed infants had abnormal VEPs compared to unmatched controls. A further pilot study described longer term visual outcomes, which included nystagmus, reduced visual acuity and strabismus, in a selected group of infants and children exposed to methadone in utero, thus informing clinical and electrophysiological assessment at six months of age. The pilot studies were followed by a major prospective cohort study. Prospective Study: One hundred and two term infants of mothers prescribed substitute methadone during pregnancy and 50 comparison infants matched for birth weight, gestation and socio-economic group were recruited in the neonatal period. Flash and flicker VEPs were recorded from the occipital scalp of infants within three days of birth. Drug exposure was determined by maternal history, maternal and infant urine and meconium toxicology. Excess alcohol exposure in utero was determined by elevated fatty acid ethyl esters in meconium. Neonatal flash VEPs were classified as mature, typical, or immature according to waveform morphology, and amplitude and latencies measured. Flicker VEPs were analysed using a fast-Fourier transformation and responses at each flicker frequency determined. The same cohort of drug-exposed and comparison infants was invited for clinical visual evaluation at six months of age in conjunction with pattern-onset VEPs and Griffiths developmental assessment. Results: Neonatal testing: Neonatal VEPs were successfully recorded from 100 drug-exposed infants and 50 matched comparison infants at a median age of 24 hours (IQR 13-44). Gestational age, birth weight and socio-economic group did not differ between groups. Flash VEPs from methadone-exposed infants had fewer P1 components (p=0.001), and were more likely to be of immature waveform (p<0.001) compared to comparisons. VEPs from methadone-exposed infants were also smaller in overall amplitude (median 27µV vs 39.5µV, p<0.001). The relative risk of an abnormal VEP in the methadone-exposed cohort was 5.6 with an attributable risk percent of 82%. The majority of infants were exposed to illicit drugs in addition to prescribed methadone, most commonly opiates (74%) and benzodiazepines (66%). VEPs did not differ between infants exposed to opiates only, those additionally exposed to benzodiazepines and those exposed to stimulants. Regression analysis confirmed that the difference in VEP parameters between drug-exposed and comparison infants was associated with methadone exposure and not other drugs of misuse. 48% of the methadone-exposed cohort developed NAS requiring pharmacological treatment; there was no association between neonatal VEPs and subsequent onset or severity of NAS. Flicker VEP analysis demonstrated an optimal flicker frequency of 4.6 Hz in both groups, but there were few differences in the proportion of responses between groups. Six month follow-up: Retention rate to six month follow-up was 79% for the methadone-exposed cohort and 52% for comparison infants. Age at assessment (median 27 weeks, range 26-30 wk), weight and OFC did not differ between groups. The demographic characteristics of comparison infants who were followed up were compared to those of comparison infants who were not followed up. There were no significant differences in birth weight (2 sample t-test p=0.445), OFC (2 sample t-test p=0.712), gestation (Mann-Whitney test p=0.984), 5-minute Apgar score (Mann-Whitney test p=0.263) or DEPCAT score (Mann-Whitney test p=0.258) between groups. Methadone-exposed infants were more likely to have visual abnormalities than comparison infants, even after correcting for excess in utero alcohol exposure (40% vs 8%; adjusted p=0.007). Abnormalities in the methadone-exposed cohort included nystagmus (11%), strabismus (25%) and reduced visual acuity (22%). The relative risk of an abnormal visual outcome in the methadone-exposed cohort was 5.1 with an attributable risk percent of 80%. Electrophysiological abnormalities persisted at six months of age: methadone- exposed infants had smaller amplitude pattern VEPs (25 μV vs 34 μV; p=0.005) with delayed peak latencies (115ms vs 99ms; p=0.019) and fewer responses at the small check size (p=0.003), compared to controls. Methadone-exposed infants had significantly lower neurodevelopmental scores compared to comparison infants (GQ 97 for cases vs 105 for controls; p<0.001), even after correcting for maternal smoking, antidepressant treatment and excess alcohol consumption during pregnancy. Infants exposed to poly-drug misuse and treated for NAS in the newborn period performed particularly poorly on their neurodevelopmental scores. Visual impairment was an independent predictor of poor neurodevelopmental outcome and most infants scoring <85 on neurodevelopmental assessment had co-existing visual problems. Conclusions: In utero exposure to prescribed methadone and other substances of misuse is associated with an alteration in visual electrophysiology in the newborn period suggestive of immature visual maturation. These changes are independent of additional benzodiazepine or stimulant exposure, and appear to be associated with prescribed substitute methadone. At six months of age, there is a high incidence of clinical visual abnormalities in infants exposed to methadone and other drugs of misuse in utero. Persistence of electrophysiological abnormalities beyond the neonatal period suggests that opiates may have a longer term effect on the developing visual system. Drug-exposed infants also have poorer neurodevelopmental scores than matched comparison infants after correcting for maternal smoking and excess alcohol intake. The bias of loss to follow-up was minimised by the high retention rate of drug-exposed infants. Although there was a higher loss of comparison infants, there were no differences in demographic characteristics between comparison infants followed up and those not followed up, suggesting the groups were similar. In addition, published data suggest the incidence of visual abnormalities described in the comparison population to be representative of the larger population. Infants born to drug-misusing mothers are highly vulnerable and warrant early comprehensive visual assessment.

Item Type: Thesis (MD)
Qualification Level: Doctoral
Keywords: Visual evoked potential, vision, drug misuse, methadone, neonate
Subjects: R Medicine > RE Ophthalmology
R Medicine > RJ Pediatrics > RJ101 Child Health. Child health services
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: Mactier, Dr. Helen and Weaver, Prof. Lawrence
Date of Award: 2012
Depositing User: Dr Laura McGlone
Unique ID: glathesis:2012-3184
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2012
Last Modified: 10 Dec 2012 14:04
URI: http://theses.gla.ac.uk/id/eprint/3184

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