Comparison of clinical and demographic characteristics of isolated positional and isolated rem-dependent phenotypes of obstructive sleep apnea syndrome

Objective: This study aimed to compare the clinical and demographic characteristics of patients diagnosed with two common phenotypes of Obstructive Sleep Apnea Syndrome (OSAS): isolated positional OSAS and isolated REM-dependent OSAS. Materials and Methods: Polysomnography (PSG) data from a total of 3,742 patients were evaluated. Thirty-five patients who met the diagnostic criteria for isolated REM-dependent OSAS were identified. In parallel, the 35 most recently evaluated consecutive patients who met the criteria for isolated positional OSAS were included. Additionally, 30 consecutive patients whose PSG results were normal were selected as the control group. Results: A total of 100 patients were included (45 women, 55 men). The proportion of males was significantly higher in the positional OSAS group (82.9%), whereas females constituted a significantly higher proportion in both the REM-dependent OSAS group and the control group (60%). All REM-dependent OSAS cases were classified as mild based on the Apnea–Hypopnea Index (AHI), while the positional OSAS group consisted of 48.6% mild, 37.1% moderate, and 14.3% severe cases. Major OSAS symptoms—snoring and witnessed apnea—were significantly less frequent in REM-dependent OSAS compared to positional OSAS (28.6% vs. 94.3%). Notably, the prevalence of snoring in the REM-dependent group was even lower than in the control group (28.6% vs. 56.7%). Diabetes mellitus and hyperlipidemia were significantly more common in the REM-dependent OSAS group than in both the positional OSAS and control groups. Similarly, the use of calcium channel blockers was significantly higher among REM-dependent OSAS patients. The mean age of the control group was significantly lower than that of the other two groups. Body weight was similar across groups; however, patients with REM-dependent OSAS had significantly shorter height and higher body mass index. The Epworth Sleepiness Scale score was significantly higher in the positional OSAS group. Hemoglobin and hematocrit values were significantly lower in the REM-dependent OSAS group. Total AHI was significantly higher in positional OSAS. The mean supine AHI (phenotypic AHI) in positional OSAS was significantly higher than the REM-AHI in REM-dependent OSAS (39.2 ± 23.5 vs. 26.3 ± 11.9). The desaturation index was also significantly higher in the positional OSAS group. Multivariate logistic regression analysis identified female sex (p = 0.035, Wald = 4.424, B = 2.073) and calcium channel blocker use (p = 0.027, Wald = 4.890, B = –2.753) as independent factors distinguishing isolated REM-dependent OSAS from isolated positional OSAS. Conclusion: The findings indicate that REM-dependent OSAS predominantly affects women, presents with low AHI values, and is often asymptomatic despite a higher burden of complications. These results do not support the traditional view of OSAS as a predominantly male disorder. We believe that a substantial number of women with OSAS may remain undiagnosed and that obese women should be carefully evaluated for OSAS even in the absence of typical symptoms. Larger, multicenter studies are needed to further clarify these findings. Keywords: Sleep apnea; sex; REM-dependent sleep apnea; positional sleep apnea; sleep apnea phenotypes; snoring; diabetes; calcium channel blocker.