Nocturic obstructive sleep apnea as a clinical phenotype of severe disease

This study was done to find whether a history of nocturia is associated with severity of obstructive sleep apnea (OSA) and also whether patients with nocturia constitute a separate phenotype of OSA.

Retrospective chart review was done in consecutive OSA patients who were diagnosed in sleep laboratory of our institute. Detailed sleep history, examination, biochemical investigations, and polysomnography reports were taken for the analysis. Nocturia was defined as urine frequency ≥2/night.

Of 172 OSA patients, 87 (50.5%) patients had nocturia. On multivariate analysis, a history of nocturia had 2.429 times (confidence interval 1.086-5.434) more chances of having very severe OSA (P = 0.031). Time between bedtime and first time for urination was significantly less in very severe OSA compared to severe OSA and mild-to-moderate OSA (2.4 ± 0.9, 3.1 ± 1.3, and 3.0 ± 1.1 h, respectively) (P = 0.021). Patients with nocturia were older (52.3 ± 11.9 vs. 47.6 ± 12.1 years; P = 0.012), had higher STOP BANG scores (P = 0.002), higher apnea-hypopnea index (AHI) (64.8 ± 35.9 vs. 43.9 ± 29.1; P < 0.001), and higher Epworth sleepiness scale (ESS) (9.2 ± 5.3 vs. 7.7 ± 4.4; P = 0.052) and were more likely to be fatigued during day (P = 0.001). Nocturics had higher body mass index (BMI) (P = 0.030), higher waist, and hip circumference (P = 0.001and 0.023, respectively). Nocturic patients had lower awake SpO₂(P = 0.032) and lower nadir SpO₂ during sleep (P = 0.002).

A history of nocturia (≥2/night) predicts very severe OSA (AHI >60). Nocturic OSA is a phenotype of OSA with more severe AHI, lower oxygen levels, higher BMI, and higher ESS. We believe nocturia can be used for screening in OSA questionnaires, which needs to be validated in further community-based studies.