Prevalence of overlap syndrome in chronic obstructive pulmonary disease patients without sleep apnea symptoms

The co-existence of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA) is a common phenomenon referred to as overlap syndrome (OS). In this study, we evaluated the prevalence of OS in mild hypoxemic COPD patients without OSA symptoms and compared characteristics of OS and COPD patients.

Forty-five COPD patients (mean FEV₁ 1671.3 ± 532.0 mL) with mild hypoxemia presenting no sleep apnea symptoms (96% men, mean age 67.7 ± 8.5 years) were involved in this study. Clinical characteristics were recorded, biochemical analysis and polygraphy were performed.

Twenty-six patients with a RDI of ≥15 events/h were defined as OS (58%). When OS (n = 26) and COPD without OSA (n = 19) groups were compared, BMI (29.6 ± 6.6 vs 25.6 ± 4.9 kg/m² ; P = 0.03), TNF-α level (24.8 ± 8.1 vs 3.6 ± 0.8 ng/mL; P = 0.03) and sleep time with SpO₂  < 90% (23.9 ± 29.4 vs 9.7 ± 21.9%; P = 0.02) were significantly increased in OS. Univariate analysis showed a correlation between RDI and BMI (P < 0.01), Epworth score (P = 0.050), COPD exacerbation frequency (P = 0.046) and TNF-α (P = 0.048). However, multivariate linear regression analysis revealed a significant correlation only between RDI and BMI (P < 0.01). BMI as a predictor of OSA was examined through ROC curve analysis and the area under curve was 0.691 (P = 0.03). To identify OS patients, BMI > 27.2 kg/m² had a sensitivity of 73% and specificity of 68%.

This findings support that high prevalence (58%) of OS in COPD patients without OSA symptoms is related to BMI. Therefore, sleep study should be considered in especially overweight or obese COPD patients, even in those without sleep apnea symptoms.