According to a report published in 2006 by the French Ministry of Health and Solidarity, approximately 20–30% of the French population complained of sleep disorders, 15–20% of whom had moderate insomnia; 9–10%, severe insomnia; and approximately 8%, excessive daytime sleepiness. These conditions each have direct consequences for public health [17]. Many studies have shown that quality of life is frequently affected by respiratory allergies, in particular among patients with moderate to severe symptoms. The related disorders include changes in mood, deterioration in cognitive function and in school and work performance, memory deficits and an inability to concentrate [5, 18,19,20,21,22,23,24,25]. Sleep disruption, sleepiness and tiredness are frequently reported by patients with AR [4, 8, 20, 23, 24, 26]. It has become increasingly clear that sleep disorders have a direct and indirect growing economic impact, and management of sleep disorders thus represents an important challenge for health systems. In our study, sleep disorders were among the most commonly cited reasons for consultation (73.5% of adults and 65.8% of children). For adults, this frequency is twice as high as that obtained in the “Sleep and Transport” yearly survey poll commissioned by the French Institute for Public Health Surveillance (INVS), which reported that 37% of French people suffered from sleep disorders [27]. For participants in the MORPHEE study, the other symptoms that were commonly reported as reasons for consultation were typical of AR [14]: rhinorrhea (71.0% of adults and 66.1% of children), nasal congestion (65.5 and 66.7%), and sneezing (65.3 and 62.8%). In addition, persistent cough was a reason for consultation in 44.1% of children. This finding might be explained by the high frequency of children suffering from asthma (48.3%). Some authors have shown that nasal congestion could be a major cause of sleep disturbance and respiratory disorders during sleep [23, 28]. Other symptoms of rhinitis (sneezing, rhinorrhea, nasal pruritus) and different components of the immune and inflammatory response could also affect sleep and sleepiness during the day [23]. The use of antihistamines was not expected to play a significant role in sleepiness because the participants were almost exclusively taking new-generation antihistamines.
The analysis of the frequency of sleep disorders according to type of AR showed that sleep disorders were more common in severe persistent AR than in other forms of AR. These results support those of the DREAM and SOMNIAAR studies, which previously showed a positive correlation between deterioration in quality of sleep and AR severity [4, 8]. Specifically, the DREAM study showed that participants with severe AR, whether persistent or intermittent, had an increased incidence of insomnia, hypersomnia, sleep apnea, sleepiness and memory problems and a significantly more regular use of sedatives and alcohol compared to those who did not have AR [4]. In the MORPHEE study, participants suffering from severe and persistent AR experienced sleep disorders significantly more frequently than participants in the other groups. This result may be associated with a potential recruitment bias related to the nature of the allergen and the SLIT indications. Indeed, the majority of participants enrolled in the MORPHEE study had severe persistent AR (63.5%), which is a primary indication for the initiation of SLIT. Only 12.0% of participants presented with intermittent AR (mild or severe).
The distribution of participants in the MORPHEE study according to AR category can be compared to those of other studies conducted among participants with AR caused by different allergens (DREAM, SOMNIAAR, ODISSEE and INSTANT studies) or with AR induced by HDM (ADARA and ANTARES studies). In the ADARA study, 75.4% of asthmatic participants (adults and children) and 79.1% of non-asthmatic participants had moderate to severe persistent AR [21]. The ANTARES study showed that 53% of children had moderate to severe persistent AR, with a mean TNSS score of 8.2 ± 2.4; these values were close to those obtained in the MORPHEE study [29]. The high proportion of persistent rhinitis observed in the MORPHEE study (80% of participants) is likely linked to the perennial nature of the allergen (HDM). Indeed, in the DREAM study, sensitization to HDM was observed in 35% of participants with intermittent rhinitis and in 72% of participants with persistent rhinitis, whereas there was no significant difference between participants sensitized to pollen: 87% had intermittent rhinitis and 72% had persistent rhinitis [30]. Therefore, the higher frequency of severe AR in the MORPHEE study may be linked to the recruitment of participants who were candidates for AIT. Indeed, according to the latest ARIA guidelines, AIT is indicated for severe and/or persistent AR that is difficult to control with symptomatic treatments alone or, in the case of rhinitis accompanied by asthma, that justify systemic treatment with AIT [14].
At the time of their consultation, nearly 80% of participants were not satisfied with their treatment before SLIT, mainly because it did not relieve their allergies (56.7%) or because the amount of drugs taken was too high (52.1%). The prescription of AIT is thus consistent with the ARIA good practice guidelines for treating respiratory allergies for patients with moderate to severe AR when symptomatic drugs and avoidance measures cannot relieve their symptoms. Unlike symptomatic treatments, AIT can significantly modify the disease in a clinically relevant way in the years following treatment and in the long term [31, 32].
As the MORPHEE study used a cross-sectional observational design, it had certain limitations. In particular, the method used to document sleep disorders did not allow for assessments of the existence or extent of bias associated with systematic questioning. However, the frequency with which sleep disturbances were reported when questions were asked to both physicians and participants via a self-reported questionnaire clearly demonstrated that sleep disorders are highly prevalent and not always accounted for in the treatment of allergic patients.
This finding highlights the importance of asking patients about the quality of their sleep during allergy consultations to better identify their problems.
Furthermore, the participating physicians may have consciously or unconsciously selected participants for the study; however, this possibility was inevitable. Although the sequential nature of enrolment helped reduce this bias and minimized the potential bias related to the enrolment of more severe participants due to their more frequent consultations, it cannot be ruled out that the participants enrolled in the MORPHEE study tended to have more severe conditions and therefore more intense sleep disorders. Although less robust than clinical trials from a methodological point of view, observational studies do, nonetheless, have the advantage of allowing “real-life” data to be collected and thus reflect routine medical practice when a sufficient number of participants has been included. Finally, the characteristics of the participants in the study were very similar to those of patients with HDM allergies who are usually seen in routine practice; this similarity allowed the results to be generalized to patients starting SLIT for HDM allergy.