## 4 Discussion
between the NT1 patients and controls in the present investigation, and the N group reported suffering from headaches similarly to the controls, in accordance with the findings by [PERSON] and coworkers [32]. The analysis of the over cut-off scores of DC/TMD Axis II did not show significant differences among groups in all questionnaires administered, except the PHQ-9, an instrument for screening, diagnosing, monitoring, and measuring the severity of depression. This is a very interesting outcome, adding value to the study, as it is in agreement with data reported in the literature. In particular, patients with NT1 showed a greater prevalence of depression with mild and moderate symptoms compared to healthy controls [60]. According to some authors, the orexinergic system could be involved in the pathophysiology of psychiatric disorders [61]. It has been suggested that orexin-1 deficiency could prevent appropriate management of emotions and it could therefore be related to depressive symptoms [62]. It is still unclear if the presence of these alterations belongs to the pathophysiology of narcolepsy or if it is secondary to its manifestation, but what is certain is the importance of monitoring the patients affected by narcolepsy for the presence of depression. The JFLS is a questionnaire that evaluates the limitations of mandibular function and, even if not significantly (\(p=0.093\)), the N group showed a trend in higher scores than the controls; 23.1% of NT1 patients had scores over cut-off, versus 7.7% of the control group. These data suggest plausible susceptibility to TMD dysfunction and discomfort in N patients. The outcomes of the present study should be interpreted in light of some limitations. Despite the fact that all the questionnaires administered were validated and internationally recognized as the gold standard for TMD diagnosis, the absence of a complete psychiatric evaluation, which would have provided more reliable descriptions of the whole spectrum of mental disorders, limits the validity of the conclusions. Furthermore, not having assessed the presence of bruxism represents a bias: despite the association between sleep bruxism and TMD, it is still a matter of debate [63]. There is growing evidence on the possible correlations between awake bruxism and orofacial pain [64]. Therefore, the presence of bruxism in the population of the present study represents a possible confounder. The non-significant differences in the PPTs of the muscles evaluated and in the prevalence of TMD in the N group, despite the high prevalence of depressive symptoms, suggest the presence of pain in these patients should be carefully considered because it seems to have a multifactorial etiology. To this end, the personal characteristics of a single patient could correspond to manifold clinical presentations. Despite having not found significant differences between the two groups, the results are of remarkable interest and should be taken into consideration in both clinical and research settings to avoid publication bias. In the present study, the narcolepsy group included only NT1, characterized by low levels of hypocretin-1, thus permitting us to evaluate the impact of hypocretin deficiency, together with REM sleep propensity and EDS. Even if hypocretin-1 has been reported to have antinociceptive effects [34; 35; 36], the results of the present study showed no differences in muscle pain sensitivity between NT1 patients and healthy controls, in accordance with the results of a previous study [33] but with a larger sample size.