Renata Carvalho Cremaschi

Chronic pain in narcolepsy type 1 and type 2 - an underestimated reality

Narcolepsy is a rare sleep disorder classified in types 1 and 2. The co‐morbidities of narcolepsy type 1, with hypocretin‐1 deficiency, are established. Hypocretin‐1 in the central and peripheral nervous systems regulates nociception and pain. However, the patients with narcolepsy type 2 have similar excessive daytime sleepiness and co‐morbidities without elucidation. The objective of the study was to determine the frequency and the characteristic of chronic pain according to the type of narcolepsy. We also investigated the effect of the interaction between the nutritional status and the type of narcolepsy. It was a cross‐sectional study using self‐administered questionnaires. Patients with narcolepsy (33 type 1 and 33 type 2), from Universidade Federal de São Paulo, Brazil, matched by age and gender to 33 control subjects were included. Both types of narcolepsy presented a high frequency of chronic pain (84.84% type 1 versus 75.75% type 2), with indistinct pain characteristics between them. The odds ratio was 20.8 in type 1 and 11.6 in type 2, compared with controls. Obese individuals with narcolepsy type 1 and type 2 did not present a significant difference in pain intensity, compared with obese controls. Patients with narcolepsy type 1 and type 2 were associated with a high frequency of chronic pain. Chronic pain emerged as a co‐morbidity never reported before in type 2. Depression possibly influences pain perception in these patients. Obesity might play a role in pain intensity in narcolepsy. The treatment of narcolepsy should take account of chronic pain, depression and obesity management.

Human hypocretin-deficient narcolepsy - aberrant food choice due to impaired taste?

Authors demonstrate that patients with narcolepsy type 1 (N1) have more tendency of eat salty snacks after satiety than health volunteers. A few mechanisms to explain the weight gain have been discussed in narcolepsy. The hypocretin-1 deficiency can influence the olfactory system. The olfactory system should be modulated through hypocretin-1 via connections from the hypothalamic to other brain regions. Likewise, hypocretin-1 can be synthesized locally in our olfactory mucosa with possible private role modulating the olfactory. In experimental studies, different kinds of smell influence the preference for type of diet. Olfactory and taste sensations help control of appetite and regulate the quantity and quality of foods that will be chosen. N1 patients have lower levels of hypocretin-1 and consequent inferior olfactory threshold, less olfactory discrimination, and these findings improved after nasal hypocretin-1 administration. It is possible that the hyposmia influenced the quality and quantity of food by narcoleptic patients. We suggest that a complementary analysis of olfactory function should be done concomitant with food preferences to compare narcoleptic patients with and without hypocretin-1 deficiency.