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Elevated Mean Diffusivity in the Left Hemisphere Superior Longitudinal Fasciculus in Autism Spectrum Disorders Increases with More Profound Language Impairment

L. Nagae,Deborah M. Zarnow,L. Blaskey,J. Dell,Sarah Y. Khan,S. Qasmieh,S. Levy,T. Roberts

Published 2012 in American Journal of Neuroradiology

ABSTRACT

The cause of autism continues to be uncertain and conventional imaging is not helpful. These investigators used DTI to study the language-related white matter tracts in a subset of patients with autism and language impairments. Eighteen patients were compared with 25 controls and showed abnormal DTI parameters in the superior longitudinal fasciculus, particularly in its temporal portion and on the left side. Thus, the white matter subserving language in these patients was abnormal. BACKGROUND AND PURPOSE: Language impairments are observed in a subset of individuals with ASD. To examine microstructural brain white matter features associated with language ability in ASD, we measured the DTI parameters of language-related white matter tracts (SLF) as well as non-language-related white matter tracts (CST) in children with ASD/+LI and ASD/−LI) and in TD. MATERIALS AND METHODS: Eighteen children with ASD/−LI (age range, 6.7–17.5 years), 17 with ASD/+LI (age range, 6.8–14.8 years), and 25 TD (age range, 6.5–18 years) were evaluated with DTI and tractography. Primary DTI parameters considered for analysis were MD and FA. RESULTS: There was a main effect of diagnostic group on age-corrected MD (P < .05) with ASD/+LI significantly elevated compared with TD. This was most pronounced for left hemisphere SLF fiber tracts and for the temporal portion of the SLF. There was significant negative correlation between left hemisphere SLF MD values and the clinical assessment of language ability. There was no main effect of diagnostic group or diagnostic group X hemisphere interaction for FA. Although there was a main effect of diagnostic group on values of MD in the CST, this did not survive hemispheric subanalysis. CONCLUSIONS: Abnormal DTI parameters (specifically significantly elevated MD values in ASD) of the SLF appear to be associated with language impairment in ASD. These elevations are particularly pronounced in the left cerebral hemisphere, in the temporal portion of the SLF, and in children with clinical language impairment.

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