Treating obstructive sleep apnea (OSA) with CPAP alone leads to insomnia resolution in a meaningful but incomplete proportion of patients with comorbid insomnia and sleep apnea (COMISA). The best available data suggest that approximately one-third of patients with coexistent chronic insomnia will have their insomnia resolve with PAP therapy alone, though a substantial majority will have residual insomnia requiring additional treatment.
Key data points
- In a longitudinal study of 442 OSA patients starting CPAP, the prevalence of chronic insomnia dropped from 51.1% at baseline to 33.0% at a median follow-up of ~20 weeks — representing roughly a 35% relative reduction in insomnia prevalence. The improvement was significantly greater in CPAP-adherent patients (≥4 h/night) compared to non-adherent patients.
- In a larger cohort of 705 OSA patients followed for 2 years on PAP, the response varied by insomnia subtype. Middle insomnia (sleep maintenance difficulty) improved most dramatically, dropping from 59.4% to 30.7% among PAP users (p < 0.001). However, initial insomnia (difficulty falling asleep) and late insomnia (early morning awakening) tended to persist regardless of PAP treatment.
Important clinical implications
Even after adequate OSA treatment, a significant proportion of patients — roughly two-thirds of those with baseline chronic insomnia — will continue to meet criteria for insomnia. This supports the concept that COMISA often involves independent pathophysiological mechanisms for each disorder, not simply insomnia as a secondary consequence of OSA. In these patients, CBT for insomnia is the gold standard of treatment, which is offered province-wide at Sleep and Wake Clinic, covered by the government.
Combined treatment is superior
The MATRICS trial (n=121) demonstrated that combining CBT-I with PAP produced significantly greater insomnia remission (ISI <8) and “good sleeper” status (PSQI <5) compared to PAP alone. A 2026 network meta-analysis of 768 patients confirmed that PAP-based combination therapies — particularly sequential CBT-I followed by PAP — were superior to PAP monotherapy for insomnia improvement. An integrated CBT-I plus PAP adherence program in veterans also showed greater improvements in sleep quality, sleep efficiency, and PAP use compared to education controls.
In summary, while treating OSA alone resolves insomnia in roughly a third of COMISA patients (particularly those with sleep maintenance difficulties), the majority will benefit from concurrent insomnia-specific treatment, most notably CBT-I.