Objective: To compare the clinical features, anthropometric indices, and polysomnographic data between different body mass index (BMI) subgroups of obstructive sleep apnea (OSA) patients.

Material and Method: The authors reviewed the data from OSA patients in Siriraj Sleep Clinic from April 2005 to September 2006. Objective measurement for sleepiness (Epworth Sleepiness Scale, ESS), anthropometric measurements [body mass index (BMI), neck circumference, thyromental distance, Mallampati’s score, and occlusion pattern] and polysomnographic recordings [apnea/hypopnea index (AHI) during REM and NREM periods, respiratory arousal index, periodic leg movement index, minimal oxygen saturation, total sleep time with oxygen saturation <90%, and desaturation index] were collected. The patients were stratified into the non-obese group and obese group if their BMI was <27 or ≥27 kg/m2 respectively.

Results: Of the total 158 patients, 71 were non-obese and 87 were obese, no difference in mean age and sex was observed, but more patients with hypertension and coronary artery disease were noted in the obese group. Mean ESS was not different between the 2 groups. In anthropometric measurements, the obese group had statistically significant large neck circumference (41.6±3.5 cm vs 37.0±2.9 cm, p<0.001), but the nonobese group had a shorter thyromental distance (56.4±11.7 mm vs 61.4±11.2 mm, p = 0.006), with no significant difference in Mallampati’s score and occlusion pattern. In polysomnographic data, the obese group had statistical significantly more severity of various indices except for AHI during the REM period and the periodic limb movement index.

Conclusion: Non-obese obstructive sleep apnea patients have more bony structural change than the obese ones as demonstrated by shorter thyromental distance. But degree of abnormalities during sleep was less severe in nearly all aspects.

Keywords: Obstructive sleep apnea; Thyromental distance; Non-obese patients