No altered fractional anisotropy in ADHD

Altered fractional anisotropy (FA) was not associated with attention-deficit/hyperactivity disorder (ADHD) in a large, longitudinal study. Continuous monitoring of disease symptoms may be more sensitive to FA than diagnostic categories. Moreover, the right cingulum angular bundle (rCAB) may play a role in the severity of hyperactive-impulsive (HI) symptoms [1].

Although ADHD has been related to differences in white matter (WM) microstructure, much remains unclear about the nature of these WM differences and the clinical aspects of ADHD they reflect. In a large longitudinal cohort, Ms Christienne Damatac (Donders Institute for Brain- Cognition and Behaviour, the Netherlands) and her colleagues assessed the association between WM microstructure and symptom severity and the development of this association was investigated over time.

Clinical and MRI data was obtained from 654 participants (322 were unaffected, 258 were affected, 74 were on the subthreshold). Follow-up data was acquired at an average of 3.73 years later in a subset of 118 people (53 unaffected, 43 affected, and 22 on the subthreshold). Automated global probabilistic tractography was applied on 18 major WM tracts and associations of clinical measures with overall brain and tract-specific FA were evaluated with linear mixed-effects regression models.

Cross-sectional results indicated a significant association between HI and inattention symptoms and FA, and temporal interaction effects with tract (both P<0.007). There were no significant associations of FA with a current or lifetime ADHD diagnosis. Lower FA in the rCAB was associated with higher HI symptom severity (P_FWE=0.045). There were no significant effects for other tracts.

Longitudinal results showed that less remission of combined HI and inattention symptoms were associated with an increased FA at follow-up (P=0.048). There was no significant association of symptom remission with FA at baseline.

These findings indicate that continuous symptom measures of ADHD may be more sensitive to subtle differences in FA than diagnostic categories are. Associations of FA with ADHD are not uniformly distributed across WM tracts and the rCAB in particular may play a role in HI symptoms.

Researchers pointed out that future directions for further research may include longitudinal region-of-interest tractography analyses in clusters which are found to be significant, the use of diffusion-weighted MRI that delivers greater resolution at the neurite level, and incorporation of dMRI data in addition to the already acquired time points [1].

 

1. Damatac CG, et al. White matter microstructure in attention-deficit/hyperactivity symptoms: cross-sectional and longitudinal effects. P.047. ECNP Congress 2020.

Posted on 2 November 20202 November 2020