This patient has pulmonary overlap syndrome, a term used to describe the association between COPD and OSA. COPD and sleep apnea-hypopnea syndrome are both common diseases, affecting 10% and 5% of the adult population over age 40 years, respectively; their coexistence, which is called overlap syndrome, can be expected to occur in approximately 0.5% of this population.8 Patients with overlap syndrome have an obstructive pattern on spirometry and are more likely to have hypoxemia, hypercapnia, and pulmonary hypertension compared with patients with simple OSA.9 In overlap syndrome, hypercapnia develops in patients with a lower BMI and at a lower apnea/hypopnea index as compared with hypercapnic patients with OHS without obstructive defects and at a higher FEV1 than hypercapnic patients with COPD alone. This patient certainly has COPD, which explains the resting hypoxia, secondary erythrocytosis, and pulmonary hypertension; however, COPD usually does not cause chronic hypercapnia at his level of obstruction. This patient also likely has OSA syndrome, but OSA alone is unlikely to cause this degree of hypercapnia and is not associated with moderate pulmonary hypertension unless associated with another cause for daytime hypoxia. This patient is not obese, which rules out OHS.
- Pulmonary overlap syndrome.
8. Weitzenblum E, Chaouat A, Kessler R, Canuet M. Overlap syndrome: obstructive sleep apnea in patients with chronic obstructive pulmonary disease. Proc Am Thorac Soc 2008;5:237–41.
9. Resta O, Foschino Barbaro MP, Brindicci C, et al. Hypercapnia in overlap syndrome: possible determinant factors. Sleep Breath 2002;6:11–8.
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