A brain PET study in patients with narcolepsy-cataplexy

To investigate brain changes in both basal and cataplectic conditions in awake patients with narcolepsy-cataplexy.

Recent insights in pathophysiology have demonstrated that narcolepsy-cataplexy is caused by early loss of hypothalamus hypocretin neurons. However, the neurophysiological mechanisms underlying sleepiness and the dramatic cataplexy reaction to positive emotion remain unclear.

Twenty-one patients with narcolepsy-cataplexy and 21 age- and sex-matched controls were included. Diagnosis of narcolepsy was fully confirmed by polysomnography, HLA DQB1*0602 and CSF hypocretin levels (n=9). Seven patients were free of all drugs, and 14 were treated with psychostimulant and/or anticataplectic drugs. (18)-F-fluorodeoxy glucose positron emission tomography procedures were performed at baseline in all subjects and during cataplexy attacks (n=2).

The authors found significant hypermetabolism in narcolepsy-cataplexy in fully awake condition in the limbic cortex specifically in the anterior and mid cingulate cortex, in the right cuneus and lingual gyrus. In contrast, no hypometabolism was found. Hypermetabolism was detected in the cerebellum and pre-postcentral gyri in treated compared with untreated patients. During cataplectic attacks, cerebral metabolism significantly increased in the bilateral pre-postcentral gyri, primary somatosensory cortex, with a marked decrease in the hypothalamus.

Hypermetabolism was found in the executive network in narcolepsy at baseline in fully awake condition. Wake state assessment during scanning appears critical to avoid results showing altered functional neurocircuitry secondary to sleepiness and not to the underlying neurological disorder per se. Finally, cataplexy attacks were characterised by a hypometabolism in the hypothalamus associated with wide bilateral brain area hypermetabolisms.