Comorbid insomnia and sleep apnea (COMISA) is a condition characterized by the simultaneous presence of obstructive sleep apnea (OSA) and insomnia, as initially reported by Guilleminault et al. [1] in 1973. OSA and insomnia share overlapping features, with 10%–40% of insomnia patients fulfilling the diagnostic criteria for OSA and 30%–50% of OSA patients having one or more insomnia symptoms [2-4]. Historically, OSA and insomnia were considered as separate and independent disorders. However, recent research has demonstrated that they frequently coexist and can significantly affect each other. For instance, insomnia symptoms have been identified as potential deterrents to compliance with positive airway pressure (PAP) therapy, the primary treatment for OSA [5-7]. Conversely, interventions aimed at insomnia have been shown to reduce the severity of OSA and improve adherence to PAP therapy [8-10].

PAP compliance is crucial in preventing complications and improving survival rates among patients with OSA [11]. Nevertheless, despite its importance, there is a relative paucity of research on COMISA, particularly regarding the impact of insomnia treatment on compliance with PAP therapy. This study endeavors to bridge this gap by investigating whether PAP therapy compliance varied between COMISA patients and OSA-only patients, as well as among COMISA patients according to their participation in insomnia clinic visits.

Table 1 presents the demographic, polysomnographic, and PAP data for the COMISA group (n=43) and the control group (n=86). The average age of participants was 59.1 years, and 58.1% were men. There were no significant differences in body mass index, apnea-hypopnea index, sleep efficiency, or wake after sleep onset between the groups. Six patients in the COMISA group were diagnosed with major depressive disorder, compared to none in the control group (P=0.001). Additionally, no significant difference was found in daily PAP usage between the two groups at 3 months (249.9±148.3 minutes for the COMISA group vs. 257.1±130.5 minutes for the control group, P=0.777) or at 9 months (188.2± 156.9 minutes for the COMISA group vs. 197.2±145.0 minutes for the control group, P=0.746). There were also no differences in the percentage of participants who used PAP, those who used the PAP device for at least 4 hours on at least 70% of nights, and the number of nights with PAP device use exceeding 4 hours between the two groups at either 3 or 9 months.

Table 2 shows the demographic and polysomnographic characteristics of the COMISA patients (n=43) according to the number of visits to the insomnia clinic. Group A comprised 20 individuals who attended the insomnia clinic at least twice within a 9-month period following PAP initiation. In contrast, Group B consisted of 11 individuals who visited the clinic once and 12 who never visited. Among those in group A, 16 patients underwent both cognitive behavioral therapy for insomnia (CBT-i) and drug therapy, while 4 received only CBT-i. In group B, five patients received both CBT-i and drug therapy, and six received only CBT-i. The remaining 12 patients in group B, who never visited the insomnia clinic, also did not receive any insomnia treatment from other physicians. No significant differences in age, sex, body mass index, polysomnographic data, or comorbidities were observed between the two groups.

Table 3 presents the PAP compliance data for COMISA patients, categorized by the number of visits to the insomnia clinic and represented by four variables. Over time, all four variables indicating PAP usage decreased in both groups. No significant difference was observed in daily PAP usage between the two groups at 3 months (265.5±145.9 minutes in group A vs. 236.3±152.3 minutes in group B, P=0.760) or 9 months (213.4±155.3 minutes in group A vs. 166.3±158.3 minutes in group B, P=0.538). Furthermore, no significant difference was found in the percentage of participants utilizing PAP at 3 months (85% in group A vs. 82.6% in group B, P>0.999) or 9 months (75% in group A vs. 69.9% in group B, P=0.745). Similarly, the percentages of participants using the PAP device for at least 4 hours on at least 70% of nights, as well as the nights with PAP device use exceeding 4 hours, exhibited no significant differences between the two groups at either the 3- or 9-month intervals.

This study aimed to compare PAP compliance between COMISA patients and OSA patients without insomnia and to determine how insomnia clinic visits impacted PAP compliance. Our findings revealed no significant difference in PAP usage between the COMISA group and the control group at both 3-month and 9-month follow-up intervals. Previous research examining the relationship between insomnia and PAP compliance has produced inconsistent findings. Wickwire et al. [5] first identified a negative correlation between PAP compliance and sleep maintenance insomnia in a retrospective analysis of 232 OSA patients. In a similar vein, Pieh et al.’s study [6] found that patients with more severe initial insomnia symptoms exhibited lower PAP compliance at the 6-month mark. These researchers suggested that patients with insomnia, especially those with difficulties initiating sleep, might struggle with PAP mask usage unless they notice immediate improvements in symptoms. In contrast, Nguyen et al. [12] observed no difference in 6-month PAP usage when categorizing 148 OSA patients by their insomnia symptom scores. Similarly, a study involving Korean patients found no difference in PAP compliance between COMISA patients and OSA patients without insomnia [13]. Our findings are consistent with those of the latter study.

In our study, we also aimed to assess the impact of insomnia clinic visits on PAP compliance. Our findings indicated that the frequency of insomnia clinic visits did not result in a statistically significant difference in PAP compliance at the 3- and 9-month marks. Previous studies have offered mixed results regarding the effect of insomnia treatment on PAP compliance. For instance, Sweetman’s randomized controlled study in 2019 found that the CBT-i group showed an increase of 1 hour in average PAP usage time at the 6-month follow-up compared to the control group, along with fewer early discontinuations [9]. Similarly, Alessi et al.’s study [10] also reported a higher rate of PAP use at 90 days in the CBT-i group than in the control group. However, Ong et al.’s study [14] found no difference in PAP compliance at 90 days between the CBT-i and control groups. In our research, although patients with more frequent visits to the insomnia clinic exhibited a higher average daily PAP usage time, a greater percentage of PAP users, and more nights with PAP use exceeding four hours, these differences were not statistically significant.

The negative results of our study may be attributable to several factors. First, interventions for insomnia may not affect adherence to PAP therapy. A previous study found that even when patients treated for insomnia experienced a reduction in the severity of their symptoms, PAP usage during the initial 90 days did not improve compared to the control group [14]. Second, the treatment for insomnia in our study may have been insufficient and there may have been a lack of uniformity in treatment methods. Insomnia treatment options include both pharmacological and nonpharmacological approaches, with CBT-i being the primary nonpharmacological treatment for chronic insomnia. In our study, there was a diversity of treatment approaches: 10 out of 43 patients received only CBT-i, while 21 patients underwent a combination of CBT-i and pharmacological treatment. This variation in methods and treatment durations among patients stands in contrast with previous studies that used standardized approaches involving several weeks of treatment and regular visits [9,10,15]. Additionally, the absence of data on changes in insomnia symptoms relative to visits to the insomnia clinic precluded the possibility of testing the aforementioned hypothesis by comparing well-controlled insomnia to poorly controlled insomnia. Finally, the retrospective nature of this study introduces certain limitations regarding the definition of study groups and controls. Due to the absence of established diagnostic criteria for COMISA, the diagnosis typically involves combining the criteria for OSA and insomnia. In our study, the COMISA cohort included patients diagnosed with OSA who were referred to the insomnia clinic, as well as those already attending an insomnia clinic at the time of their OSA diagnosis. This approach may have led to the inadvertent exclusion of COMISA patients within the broader OSA population. This point could have been clarified by collecting information on semi-quantitative test data such as Insomnia Severity Index scores at the initiation of PAP therapy [8].

Despite these limitations, this study makes a significant contribution to the research on PAP compliance among patients with OSA who also have comorbid insomnia, as well as the impact of visits to an insomnia clinic. We analyzed clinical data from a tertiary referral hospital, and we found that PAP therapy compliance in patients with COMISA was not significantly different from that in patients with OSA alone. Additionally, the frequency of visits to the insomnia clinic did not result in a significant difference in PAP compliance at either the 3-month or 9-month intervals. Given these findings, there is a clear need for future prospective studies with larger patient cohorts to delve deeper into this complex relationship and to provide more definitive conclusions about the factors that influence PAP compliance in individuals with both comorbid insomnia and OSA.