Obesity Hypoventilation Syndrome Choosing the Appropriate Treatment of a Heterogeneous Disorder Amanda J. Piper, PhD a,b, *, Ahmed S. BaHammam, MD c,d , Shahrokh Javaheri, MD e,f,g BACKGROUND Obesity hypoventilation syndrome (OHS) is characterized by chronic awake hypercapnia (PaCO 2 >45 mm Hg, at sea level) and sleep disor- dered breathing in obese individuals (body mass index [BMI] >30 kg/m 2 ) in the absence of any other explanations for chronic hypercapnia. 1–3 When Burwell and colleagues 4 first described this condition as a Pickwickian syndrome, treat- ment options were limited: weight loss, tracheos- tomy, and short-term respiratory stimulants. The key contribution of sleep disordered breathing to Disclosure statement: A.J. Piper has received lecture fees from ResMed Australia and Philips Respironics, man- ufacturers of positive airway pressure (PAP) devices. She also received grant money from the ResMed Founda- tion to conduct a trial evaluating PAP therapy in obesity hypoventilation syndrome. A.S. BaHammam and S. Javaheri report no conflict of interest. a Sleep Unit, Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Missenden Road, Camperdown, New South Wales 2050, Australia; b Central Medical School, University of Sydney, Sydney 2006, New South Wales, Australia; c The University Sleep Disorders Center, Department of Medicine, College of Medicine, King Saud University, Riyadh 11324, Saudi Arabia; d National Plan for Science and Technology, King Saud University, Riyadh 11324, Saudi Arabia; e Montgomery Sleep Laboratory, Bethesda North Hospital, Cincinnati, OH 45242, USA; f Pulmonary and Sleep Medicine, University of Cincinnati, Cincinnati, OH, USA; g Division of Cardiology, Ohio State University, Columbus, OH, USA * Corresponding author. Sleep Unit, Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hos- pital, Missenden Road, Camperdown, New South Wales 2050, Australia. E-mail address: amanda.piper@sydney.edu.au KEYWORDS  Obesity hypoventilation syndrome  Continuous positive airway pressure  Hypercapnia  Nocturnal hypoventilation  Sleep disordered breathing KEY POINTS  Obesity hypoventilation syndrome (OHS) covers a spectrum of sleep breathing abnormalities from predominantly repetitive obstructive apneas, combined obstructive apneas with sleep hypoventilation, or isolated sleep hypoventilation.  There is no strong evidence to recommend one form of positive airway pressure (PAP) therapy over another in terms of clinical outcomes in OHS with concomitant obstructive sleep apnea.  Response to PAP seems to be influenced by adherence to therapy and the OHS phenotype being treated.  Cardiovascular risk remains high despite effective PAP therapy.  Weight loss and reduced sedentary behavior are important components of a comprehensive management program for these individuals. Sleep Med Clin - (2017) -–- http://dx.doi.org/10.1016/j.jsmc.2017.07.008 1556-407X/17/Ó 2017 Elsevier Inc. All rights reserved. sleep.theclinics.com