Research Staff University of British Columbia Faculty of Medicine Vancouver, British Columbia, Canada
Background: White matter injury (WMI) in preterm neonates is characterized by focal areas of white matter necrosis (punctate WMI) and more diffuse impairments in white matter (dysmaturation). White matter dysmaturation is reflected as lower fractional anisotropy (FA) measured by diffusion tensor imaging (DTI). Reduced white matter FA in neonatal DTI has been associated with adverse motor function at early ages in children born preterm. Yet, how white matter FA at school-age relates to motor function at this later age is largely unknown. Objective: To assess the relationship between white matter FA and motor function at 8 years of age in children born very preterm. Design/Methods: 110 children born very preterm (mean birth gestational age [GA] 28.19 weeks, range 24-32 weeks) completed MRI scans in the neonatal period and again at 8 years of age (mean age 8.35 years, SD = 0.38). Neonatal WMI was quantified on the neonatal T1-weighted images with significant WMI defined as WMI volume > 40 mm3. FA at 8 years was assessed using tract-based spatial statistics (TBSS). Movement Assessment Battery for Children, 2nd Ed (M-ABC-2) was used to assess fine and gross motor function at 8 years of age. Motor outcomes from the M-ABC total score were grouped as: Significant Movement Difficulty < 56 (below 5th percentile, n = 31), At-risk of Movement Difficulty 57-67 (5th-15th percentile, n = 23), and Unlikely to Have Movement Difficulty > 68 (above 15th percentile, n = 56). FA in the white matter skeleton was compared between motor outcome groups using threshold-free cluster enhancement (TFCE), adjusting for birth GA and significant WMI, and correcting for multiple comparisons across skeleton voxels using permutation testing with 5000 permutations. Results: Table 1 outlines descriptive differences in the three motor outcome groups. Children born preterm who are Unlikely to Have Movement Difficulty at 8 years had significantly higher FA (p < .05) compared to those At-risk of or with Significant Movement Difficulty, especially in the corpus collosum (Figure 1), controlling for birth GA and significant neonatal WMI. Those with Significant Movement Difficulty had the lowest FA.
Conclusion(s): In children born preterm at age 8 years, white matter FA is associated with motor performance, independent of significant neonatal WMI. Our findings indicate that white matter dysmaturation persists and has functional significance through school-age.
