Differences in brain morphological findings between narcolepsy with and without cataplexy

Abstract

Objective: Maps of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) obtained by diffusion tensor imaging (DTI) can detect microscopic axonal changes by estimating the diffusivity of water molecules using magnetic resonance imaging (MRI). We applied an MRI voxel-based statistical approach to FA and ADC maps to evaluate microstructural abnormalities in the brain in narcolepsy and to investigate differences between patients having narcolepsy with and without cataplexy.

Methods: Twelve patients with drug-naive narcolepsy with cataplexy (NA/CA), 12 with drug-naive narcolepsy without cataplexy (NA w/o CA) and 12 age-matched healthy normal controls (NC) were enrolled. FA and ADC maps for these 3 groups were statistically compared by using voxel-based one-way ANOVA. In addition, we investigated the correlation between FA and ADC values and clinical variables in the patient groups.

Results: Compared to the NC group, the NA/CA group showed higher ADC values in the left inferior frontal gyrus and left amygdala, and a lower ADC value in the left postcentral gyrus. The ADC value in the right inferior frontal gyrus and FA value in the right precuneus were higher for NA/CA group than for the NA w/o CA group. However, no significant differences were observed in FA and ADC values between the NA w/o CA and NC groups in any of the areas investigated. In addition, no correlation was found between the clinical variables and ADC and FA values of any brain areas in these patient groups.

Conclusions: Several microstructural changes were noted in the inferior frontal gyrus and amygdala in the NA/CA but not in the NA w/o CA group. These findings suggest that these 2 narcolepsy conditions have different pathological mechanisms: narcolepsy without cataplexy form appears to be a potentially broader condition without any significant brain imaging differences from normal controls.

Figure 1. Clusters showing significant main effects of group on ADC value between patients having narcolepsy with cataplexy (NA/CA) and normal control (NC).

1-1) ADC values were higher in the left parahippocampal gyrus (Brodmann area 34) and amygdala, and 1-2) in the left inferior frontal gyrus (Brodmann area 47/11) in NA/CA than in NC, while these values were lower in 2) the left postcentral gyrus (Brodmann area 3) in the former group. pone.0081059.Results.tifare significant at FWE-corrected p<0.05. Color scale is for F statistic.

Figure 2. Clusters showing significant main effects of group on ADC and FA values between the narcolepsy with cataplexy (NA/CA) and narcolepsy without cataplexy (NA w/o CA) groups.

a) ADC value was higher in the right inferior frontal gyrus (Brodmann area 9) for the NA/CA group than for the NA w/o CA group. b) In the NA/CA group, the FA value in the right parietal lobe (precuneus) was higher than that in the NA w/o CAgroup. Results are significant at FWE-corrected p<0.05. Color scale is for F statistic.