Preface for the 3rd Clinical Update Sleep, 23rd February 2018, Royal College of Physicians, London, UK: year in review

Abstract

Sleep medicine remains an exciting and fast-evolving field of medicine with insomnia, hypersomnia, parasomnia, sleepdisordered breathing and circadian rhythm disorders affecting significant proportions of the population. This update provides a selected overview about recent publications in the field. Sleep-disordered breathing and comorbidities The high prevalence of obstructive sleep apnoea (OSA) differs between genders, with male patients being more affected (1). In a US-nationwide study of 1,704,905 patients who had a diagnosis of OSA and 1,704,417 controls matched for age, sex and state of residence, the prevalence of co-morbidities [OR (95% CI)], such as type 2 diabetes [2.29 (2.28-2.31)], cardiac arrhythmia [3.26 (3.20-3.32)], ischaemic heart disease [2.54 (2.51-2.56)], stroke [3.51 (3.42-3.60)], hypertension [2.14 (2.13-2.15)], depression [4.99 (4.91-5.07)] and congestive heart failure [4.30 (4.21-4.39)] was increased (2). Non-communicable disease is important (3) and its link with comorbidities, predominantly its association with obesity (1), make OSA an important confounding factor that impacts on physical, social and mental health (4). Diagnostic criteria for sleep apnoea There have been ongoing discussions about the classification and diagnostic parameters of OSA. Study outcomes investigating OSA are dependent on accurate description, definition and comparisons of their patient groups. Heinzer et al. argue that the present International Classification of Sleep Disorders (ICSD-3) definition of sleep apnoea yields an unrealistically high prevalence of OSA (5), in part related to a low apnoea-hypopnoea index (AHI) threshold for normal subjects (5/h) and a high prevalence of coexisting symptoms and conditions such as fatigue, insomnia and hypertension which may not be related to the underlying OSA (6). In a group of 2,121 patients who underwent full home polysomnography (PSG) ['HypnoLaus' cohort; 48% male, median age 57, (interquartile range, IQR 49-68) years, mean body mass index (BMI) 25.6 kg/m 2 , standard deviation (SD) 4.1 kg/m 2 ], they applied the 2013 American Academy of Sleep Medicine (AASM) criteria for OSA: An apnoea was defined as ≥90% reduction in airflow from baseline, lasting for ≥10 seconds; a hypopnea was defined as ≥30% reduction in airflow from baseline, lasting for ≥10 seconds with either a ≥3% drop in oxygen saturation or an arousal (7,8). These criteria led to a diagnosis of moderate-to-severe OSA (sOSA) (AHI ≥15/h) in 23.4% (95% CI: 20.9-26.0) of women and 49.7% (95% CI: 46.6-52.8) of men (9). However, analysing the same cohort in 2016, but using the ICSD-3 criteria which are defined by an AHI ≥15/hour, or an AHI ≥5/hour associated with one or more symptoms of OSA or cardiovascular and metabolic comorbidities, the prevalence of OSA increased to 74.7% of men, and 52.1% of women (5,6,10). The authors suggested that a better definition of OSA should be sought using prospective and large cohort follow-up studies. Screening for OSA in a bariatric population OSA and obesity commonly co-exi...