Decreased occipital volume as a trait marker for adults with ADHD? Evidence from a voxel-based morphometry study

Aims: Fronto-striato-cerebellar networks (FSCN) are widely accepted to play a major role in the pathophysiology of attention deficit hyperactivity disorder (ADHD). Recent studies point to a possible contribution of the visual cortex in regulating visuo-spatial attention. To our knowledge there are no morphometric imaging studies that particulary address the question of a possible involvement of visual brain areas in the pathogenesis of adult ADHD.

Purpose: In order to analyse a possible involvement of FSCN in the pathogenesis of adult ADHD we applied the technique of optimized voxel-based morphometry (VBM) to a large sample of adult ADHD patients and controls.

Methods: The data are part of the Freiburg ADHD Imaging Study in Adults (FAISA). For this subproject 31 unmedicated patients (aged 31.2±9.7) and 31 healthy controls (aged 31.5±8.6) were individually matched for age and gender. Diagnosis of ADHD was based on DSM-IV criteria and psychometric assessment [BDI, ADHD check list, Wender-Utah-Rating-Scale (WURS-25)]. T1-weighted scans were obtained on a 1.5T Siemens Sonata scanner (160 sagittal slices, 1.0×1.0×1.0mm³) and analyzed using optimized VBM with SPM2. Results were considered significant at P<0.05 corrected with FDR (false discovery rate).

Results: We found a large area of decreased gray matter (GM) volume in each occipital lobe (right: P=0.043, cluster size 5309 voxels; left: P=0.043, 2423 voxels), mainly in V1 and V2. There was a trend towards correlation between volume loss and scores on the WURS (P=0.079).

Conclusions: In this first VBM study of adult patients with ADHD we find large areas of significant volume loss bilaterally in the occipital lobe the severity of which correlated as a trend with WURS scores. This finding is in line with several reports in ADHD in children. We could not replicate findings of FSCN volume alterations in children. Structural abnormalities of the visual cortex might be a trait marker of ADHD. In the pathophysiology of ADHD they might be associated with deficits in regulating visuo-spatial attention. Prefrontal and striatal morphometric abnormalities could be closer linked with the particular present psychopathology of individual ADHD patients like impulsivity or hyperactivity. Further research should clarify whether abnormalities of the visual cortex are the result of locally disturbed network activity (bottom-up-mechanism) or secondary to prefrontal attentional network dysfunction (top-down-mechanism).

Figure 1: Representation of gray matter volume loss in the glass brain