MR neuroimaging and pons proton spectroscopy in type 1 narcolepsy
Stefania Evangelisti1, Claudia Testa2, Laura Ludovica Gramegna1,3, Fabio Pizza3,4, David Neil Manners1, Elena Antelmi3,4, Lia Talozzi1, Claudio Bianchini1, Giuseppe Plazzi3,4, Raffaele Lodi1,3, and Caterina Tonon1,3

1Department of Biomedical and NeuroMotor Sciences, Functional MR Unit, University of Bologna, Bologna, Italy, 2Department of Physics and Astronomy, University of Bologna, Bologna, Italy, 3IRCCS Istituto delle Scienze Neurologiche di Bologna, Bologna, Italy, 4Department of Biomedical and NeuroMotor Sciences, University of Bologna, Bologna, Italy


Narcolepsy type 1 (NT1) is a rare and life-long disease, characterized by central hypersomnia and cataplexy typically triggered by emotions. NT1 is linked to a selective loss of hypothalamic hypocretin neurons. To characterise neurodegeneration, we combined pons 1H-MRS and whole brain structural analysis in a large and homogenous sample of adult NT1 patients. 1H-MRS showed evidence of pontine neuronal dysfunction, consistent with its key role in REM sleep regulation. Grey matter loss was detected in brain regions implicated in the disease pathophysiology, including frontal-prefrontal cortices, putamen nuclei, thalami, hypothalamus, amygdalae, cerebellum, and widespread subtle tissue microstructural alterations were also found.


Narcolepsy type 1 (NT1) is a rare central sleep disorder characterized by excessive daytime sleepiness and cataplexy, i.e. sudden episode of paralysis of voluntary muscle triggered by strong emotions, sleep paralysis, hypnagogic hallucinations and disrupted nocturnal sleep1. NT1 is caused by loss of orexin-producing neurons in the postero-lateral hypothalamus, which project to widespread brain and brainstem areas2. Most previous proton MRS studies of NT1 patients have focused on neurodegenerative changes in hypothalamus3,4,5, while in the pons inconsistent results regarding metabolites concentrations have been found in limited cohorts6,7. Similarly, previous structural neuroimaging studies have shown controversial results consistent with the inhomogeneity of study population and image analysis methods employed8. The aim of this study was to test for metabolic alterations in the pons by 1H-MRS, and to brain grey and white matter alterations by VBM and TBSS analyses, in a large cohort of adult NT1 cases.


We evaluated 44 NT1 patients, who underwent brain MR in their diagnostic workup to exclude symptomatic forms due to other neurological diseases. Acquisitions were performed with a 1.5T GE scanner, equipped with a head coil. The standardized MR protocol included single voxel 1H-MR spectroscopy (PRESS) with localization in the pons (TR/TE=1500/40ms; NS=512, volume of interest mean[SD] 1.78[1.09] ml), volumetric T1-w images (TR/TE/TI=12.5/5.1/600ms, 1mm3 isotropic) and diffusion-weighted MRI (TR/TE=10.000/87.5ms, 25 directions, b-value=900 mm2s−1, voxel=1.25x1.25x4mm). Not all the patients completed the whole protocol; groups of sex- and age-matched healthy controls were included in the analysis (Table 1). Spectral analyses were performed with LC Model 6.3, and N-acetyl-aspartate (NAA), choline (Cho) and myo-Inositol (mI) concentrations were expressed relative to creatine (Cr). Voxel-based morphometry (VBM) analyses were performed on T1-w images using SPM 12.0. After a bicommissural realignment and tissue segmentation, grey matter images were aligned to an iteratively-created study specific template (DARTEL), registered to the MNI-152 template and spatially smoothed (gaussian kernel, FWHM 5mm). Diffusion-weighted data underwent standard pre-processing and tensor fitting. Voxelwise analysis of tensor parameters was then performed using TBSS (Tract-Based Spatial Statistics). Fractional anisotropy (FA) images for all subjects were non-linearly aligned, a mean FA image was created and thinned to create a skeleton representing the centres of all tracts common to the group. Each subject's data was then projected onto this skeleton and the resulting data fed into voxelwise cross-subject statistics. Similar comparisons were performed on MD (mean diffusivity), AD (axial diffusivity) and RD (radial diffusivity) maps. Group comparisons were performed with univariate analyses (SPSS®); voxelwise comparisons were non-parametric (permutation method) with age and sex (and TIV for VBM) as nuisance regressors. Statistical significance was set to p<0.05 (corrected for multiple comparisons).


NAA/Cr and NAA/mI were significantly lower in patients compared to controls (Table 2). Figure 1 shows the voxel localization of pons spectroscopy and two spectra, acquired from a HC subject and an NT1 patient, showing the reduced NAA content. VBM analysis revealed grey matter density loss for NT1 patients mainly in precentral and postcentral gyri, frontal gyri, frontal pole, frontal operculum cortex, frontal orbital cortex, lateral occipital cortex, insular cortex, bilateral putamen nuclei, bilateral thalami, hypothalamus, amygdala, hippocampus, temporal poles and cerebellum (Figure 2). MD and AD values were found significantly higher in NT1 patients, mainly in corpus callosum, frontal white matter, corticospinal tract and thalamic area (Figure 3). Differences in FA and RD values between patients and controls were slightly below the significance threshold.

Discussion and conclusions

Pons is considered a central structure in the pathophysiology of NT1, because of the presence of the reticular regions implicated in REM sleep regulation9 and circuits involved in muscle paralysis during cataplexy1, but consistent alterations have not as yet been observed using advanced MRI techniques. This study demonstrated in NT1 patients a neuro-axonal degeneration in the pons (lower NAA/Cr and NAA/mI) related to its inability in the inhibition of REM sleep. In comparison to previous pons MRS studies, our cohort size is larger and homogeneous regarding the presence of cataplexy. As for the morphological and microstructural aspects, we found decreased grey matter in all brain regions involved in the pathophysiology of the disease (Figures 1,2) in particular in the medial prefrontal cortex that receives excitatory projection from the hypothalamus, in areas involved in the emotional circuit (insula and hippocampal) and in the cerebellum10, and TBSS showed subtle widespread microstructural alterations rather than focal loss of integrity in multiple white matter tracts.


No acknowledgement found.


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Table 1. Demographic summary of patients and healthy controls. Subgroups for different MR data are reported. No significant differences in age and sex between patients and controls were found for any subgroup (as assessed with Mann-Whitney and Pearson-χ2 respectively). NT1: Narcolepsy Type 1 patients; HC: healthy controls; N: number of participants, M: male, F: female; MRS: Magnetic Resonance Spectroscopy.

Table 2. MRS results. Results for the MRS metabolites concentrations that were investigated within the pons. Significant results that survived Bonferroni correction (p=0.0125) are in bold. NT1: Narcolepsy Type 1 patients, HC: healthy controls, NAA: N-acetyl-aspartate, Cr: Creatine, Cho= choline, mI: myo-Inositol.

Figure 1. Pons 1H-MRS. Illustrative localization of the volume of interest in the pons is shown on a sagittal view of the MNI-152 template, along with grey matter loss evinced by VBM analysis. Two representative pons proton spectra, acquired from a NT1 patient and a healthy control, are shown.

Figure 2. VBM comparison results. Evaluation of grey matter loss in NT1 patients. P-values maps (p<0.05 corrected for multiple comparisons) are shown projected onto the study-specific template. NT1: Narcolepsy Type 1 patients; HC: healthy controls.

Figure 3. TBSS comparison results. Mean diffusivity and axial diffusivity maps are shown. Fractional anisotropy (FA) and radial diffusivity did not shown significant alterations. P-values maps (p<0.05, corrected for multiple comparisons) are reported in red projected onto the group mean FA image and white matter skeleton (in green). MD: mean diffusivity; AD: axial diffusivity; NT1: Narcolepsy Type 1 patients; HC: healthy controls.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)