Wednesday, April 25, 2012

Study: MRI sheds light on cognitive risks for very preterm infants

White matter injury on term MRI of very preterm-born infants is predictive of future cognitive impairment, according to a study published in the May issue of Pediatrics. This discovery further supports the benefit of obtaining term MRI for very preterm-born infants, according to the authors.

“Because ultrasound scans are insensitive to most MRI findings, early MRI may help identify a group of very preterm born infants with an increased risk of later cognitive impairment,” wrote Osuke Iwata, MD, of the department of paediatrics and child health at Kurume University School of Medicine in Kurume, Japan, and colleagues. “Such information may provide an important key to improve follow-up strategies and to allow better risk stratification for future clinical trials which enroll very preterm born infants.”

While previous studies have demonstrated associations between white matter injury and cognitive impairment in very preterm-born children, this study is the first longitudinal study comparing term MRI findings, based on an MRI completed at term age, with outcomes at nine years old, according to the authors.

Seventy-six very preterm-born infants were imaged as part of the prospective study. Neurodevelopmental outcomes were assessed at 9 years old in 60 subjects using the Wechsler Intelligence Scale for Children, which tests different IQ indices.

Overall, mildly low intelligence scores (less than 85) were observed in 23.3 percent of the study cohort for verbal IQ, 41.7 percent for performance IQ and 30 percent for full-scale IQ. Moderately low scores (less than 70) were observed in 3.3 percent for verbal IQ and 11.7 percent for both performance IQ and full-scale IQ. Cerebral palsy was diagnosed in 10 percent of the children and 56.7 percent required special assistance at school.

Abnormal white matter appearances on the term MRI were predictive of mildly and moderately low performance and full-scale IQ scores, as well as cerebral palsy and the need for special assistance at school. It was also predictive of mildly low verbal IQs, but not moderately low verbal scores. Abnormal gray matter appearances did not predict any of the outcome measures.

“In very preterm born children, reduced cortical gray matter volume has also been associated with poor cognitive outcome at school age. In our current study, abnormal gray matter appearances at term were associated with the presence of white matter injury but not with any of the outcome measures at nine years old,” wrote Sachiko Iwata, MD, and colleagues. They explained that cortical gray matter lesions may contribute less to later cognitive functioning because neurologic functioning associated with gray matter injury may be affected more by other factors, such as education and family environment.

The authors concluded that term MRI may be able to help screen preterm-born infants and aid in earlier diagnosis of cognitive impairment.

“Additional studies with longer follow-up periods are still required, because neurodevelopmental assessments performed at early childhood period may not reflect cognitive functioning at school age and thereafter, either because of the limited reliability of early assessment tools or because cognitive function itself may significantly alter under the influence of numerous intrinsic/extrinsic factors such as plasticity, compensation, reorganization of injured brain, environment, and education.”

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