The bidirectional link between sleep and pain is a widely accepted concept. While there has been much focus on this in recent years, studies investigating obstructive sleep apnoea (OSA) and chronic pain are still not very common, especially in context of continuous positive airway pressure (CPAP) therapy.

In this study, people recently diagnosed with OSA, a common sleep disorder, that are receiving a CPAP mask are asked to fill in questionnaires at baseline, 3- and 6-month follow-up. Data of people with and without chronic pain will be collected and we will use the data will allow us to answer a number of clinically relevant questions. The primary questions investigate the following: 1) The association of CPAP adherence and pain outcomes with CPAP therapy at 3-month follow-up; 2) The association of baseline Apnoea-Hyopnea-Index on pain outcomes with CPAP therapy at 3-month follow-up. Secondary questions investigate the relevance of co-morbid insomnia (COMISA), the influence of chronic pain on CPAP adherence and general clinical outcomes of CPAP therapy in people with chronic pain.

In this study, participants with obstructive sleep apnoea (OSA) that start continuous positive airway pressure (CPAP) treatment will be asked to fill in questionnaires at baseline and two follow-up time points (3 and 6 months after the start of CPAP treatment). This information, information on CPAP adherence and information from the polysomnography assessment every participant has undergone prior to starting CPAP will allow us to investigate relevant outcomes of CPAP therapy in people with chronic pain. The detailed research questions are the following:

Primary research questions Longitudinal

1. Are average hours of CPAP use per night (continuous variable) associated with average pain intensity at 3-month follow-up in people with CP and OSA?
2. Is AHI at baseline associated with average pain intensity at 3-month follow-up in people with CP and OSA?

Secondary research questions Cross-sectional

1. Is there a difference in CPAP use in hours (measured at 3-month follow-up) between people with OSA-only, OSA and CP, OSA and comorbid insomnia (COMISA - defined via the Insomnia Severity Index ≥15) and COMISA with CP?
2. What is the prevalence of CP in patients with clinically relevant OSA in a sleep clinic setting?
3. Is there a difference in average pain intensity between people with OSA and CP and people with COMISA and CP?

Longitudinal

1. What are the short- (3 months) and long-term (6 months) clinical outcomes (average pain intensity, fatigue, sleepiness, sleep quality, depression, anxiety, quality of life) of CPAP treatment for patients with clinically relevant OSA and comorbid CP?
2. Does average pain intensity measured at 3 and 6-month follow-up differ between patients that show CPAP adherence (= use of CPAP for a minimum of four hours each night on at least 70% of the monitored nights) compared to patients with non-adherence (= use of CPAP for a less than four hours each night on at least 70% of the monitored nights)?
3. Is average pain intensity at baseline a predictor for CPAP adherence in people with CP and comorbid clinically relevant OSA as measured at 3-month follow-up.
4. Is there a difference in pain outcomes measured at follow-up points at 3 and 6 months between people with CP and COMISA compared to patients with only OSA and CP?
5. Is there a difference in self-reported health status with CPAP therapy at 3 and 6-month follow-up between people with clinically relevant OSA and CP compared to those without CP?
6. Are average hours of CPAP use per night (continuous variable) associated with average pain intensity at 6-month follow-up in people with CP and OSA?
7. Is AHI at baseline associated with average pain intensity at 6-month follow-up in people with CP and OSA?

Sensitivity and subgroup analyses will analyse data for people with headaches and other chronic pain separately considering headaches to be a very common direct consequence of OSA.

Inclusion Criteria:

• Participants must be 18 years of age or older
• Participants must be able to read and write in Dutch, French or English
• Participants must be diagnosed with clinically relevant OSA and newly start CPAP treatment:
• AHI ≥ 15
• Prescribed CPAP for the first time as a treatment for their OSA
• Participants must have read and signed the ICF

Exclusion Criteria:

• Participants who are currently receiving CPAP treatment or have had a CPAP treatment in the last year
• Participant receiving CPAP for other conditions than OSA (e.g. Central Sleep Apnoea)

The target group for the study consists of adult, Dutch, French or Englisch speaking patients who have been referred to the sleep clinic. These patients have been diagnosed with OSA and will start to receive CPAP treatment. They are included independent of their chronic pain status but some analyses will be done in sub-groups.