Distribution of neurochemical abnormalities in patients with narcolepsy with cataplexy: An in vivo brain proton MR spectroscopy study

Narcolepsy with cataplexy is characterised by excessive daytime sleepiness, sudden drops of muscle tone triggered by emotions, termed cataplexy, disrupted nocturnal sleep and other dissociated rapid eye movement (REM) sleep phenomena. Narcolepsy has been linked to a loss of hypothalamic neurons producing hypocretins, neuropeptides implicated in the regulation of the arousal system. Neuroimaging and neurometabolic studies have shown the pathophysiological involvement of other brain structures such as cerebral cortex and thalamus, but, overall with inconsistent results. We investigated, by using an advanced quantitative MR technique, proton MR spectroscopy (¹H-MRS), the distribution of brain neurochemical abnormalities in narcolepsy with cataplexy patients. Single voxel ¹H-MRS study was performed in the thalamus, hypothalamus, and parietal-occipital cortex of hypocretin deficient, narcolepsy with cataplexy patients, HLA-DQB1*0602-positive, drug free. No significant changes were detected in the thalamus and parietal-occipital cortex of the patients. On the other hand, the neuronal marker N-acetyl-aspartate was reduced in the hypothalamus of narcolepsy with cataplexy patients compared to controls. These ¹H-MRS findings further support that in narcolepsy with cataplexy patients, the hypothalamus is the primary site of neural lesions. The absence of ¹H-MRS neurodegenerative changes in the thalamus and cerebral cortex suggests that the abnormalities detected in these brain regions by other neuroimaging techniques are likely of functional nature.