Obstructive sleep apnea in normal weight patients: characteristics and comparison with overweight and obese patients

To determine the frequency of obstructive sleep apnoea (OSA) and metabolic syndrome (MS) in normal weight patients and their characteristics, and to compare these with overweight and obese patients.

We studied all patients with suspected OSA referred to the sleep laboratory from January to December 2009. OSA was diagnosed when the apnoea-hypopnoea index (AHI) was >5 and symptoms were present. MS was diagnosed according to International Diabetes Federation (IDF) criteria. The patients were distributed into 3 groups according to body mass index (BMI): normal weight (<25kg/m(2)), overweight (25-29.9kg/m(2)) and obese (≥30kg/m(2)).

We studied 475 patients: 7.60% normal weight and 56.4% obese. Most patients in the normal weight group were women, snorers, non-smokers, non-drinkers and were significantly younger and with a smaller neck and waist circumference than obese and overweight patients. OSA was diagnosed in 90.10%: 77.70% normal weight. OSA in these patients was mostly mild, and there were differences between the diagnosis of OSA and the BMI classified. MS was diagnosed in 64.40%: 33.33% normal weight. There was a higher probability of MS as the BMI increased. OSA and MS frequency in normal weight patients was 22% and in obese patients was 70.52%. OSA in normal weight patients was related with gender and age. There was no relationship between OSA and MS, or between otorhinolaryngological malformations and OSA in normal weight patients. Eight normal weight patients with OSA were treated with continuous positive airway pressure (CPAP) therapy.

The frequency of OSA in normal weight patients was lower than in overweight and obese patients. The frequency of concomitant OSA and MS was lower in normal weight patients than in obese subjects. Normal weight patients were mostly women, younger and had no toxic habits. In normal weight patients, age and gender were predictive factors for OSA, but OSA and MS were not related.