Nocturia is a common urological problem with a high prevalence (up to 60%) especially in elderly patients (1). The underlying causes for nocturia are various, such as conditions causing sleeping disorders, bladder storage problems, and nocturnal polyuria. Patients with nocturnal polyuria have an increased production of urine during nighttime (i.e. one third or more of the total volume of urine produced in 24-hours) (2). Nocturnal polyuria may be present in patients with obstructive sleep apnea (OSA) and treatment with continuous positive airway pressure (CPAP) reduces nighttime frequency and nocturnal voided volume in patients with OSA (3). 
In this study, we examined the amount of patients with nocturnal polyuria that suffer from OSA.
Subsequently, we offered patients with confirmed OSA treatment with CPAP, and analyzed the effect on episodes of nocturia and the nocturnal polyuria index (NPi= voided volume during night time/voided volume in 24 hours*100).

Consecutive male and female patients with nocturnal polyuria presented at the outpatient clinic of the department of Urology of a large teaching hospital, between February 2019 to September 2019, were referred to the department of Pulmonology for evaluation of OSA. Included patients had nocturnal polyuria as defined by a NPi of >20% for patients under 65 years of age and NPI >33% for patients above 65 years. Patients with diabetes mellitus, diabetes insipidus, heart failure, hypoaldosteronism, neurologic disorders (i.e. Parkinson’s disease, multiple sclerosis, spinal cord lesions) and patients with concomitant medication use (i.e. SSRI, diuretics, tetracycline, Lithium, Calcium-channel blockers, vasopressin analogues) were excluded from the study.
Polygraphy (PG) was performed at all patients, in an ambulant setting with SOMNOtouch™ RESP (SOMNOmedics GmbH, Randersacker, Germany) during one night, according to the guidelines of the American Academy of Sleep Medicine. The apnea hypopnea index (AHI) and 3-day voiding diaries were analyzed pre and post CPAP treatment.
Patients with OSA diagnosed by PG were offered a trial treatment with CPAP (DreamStation CPAP device, Philips Respironics), irrespective of severity of symptoms. During the eight-week treatment period, patients were monitored with the online monitoring system EncoreAnywhere™ (Philips, Eindhoven, the Netherlands) at week 1, 2 and 4. After 8 weeks, patients were seen at the outpatient clinic of the department of Pulmonology for a final evaluation. The definition of CPAP compliance was a minimum of 4 hours of sleep with at least 70% of the sleep time wearing the CPAP device. Post treatment evaluation was done by recording of the AHI by the CPAP device. Episodes of nocturia and nocturnal voiding volumes were extracted from a three-day voiding diary. Statistical analysis was done by using a Wilcoxon Matched-Pairs because of the small sample size.

Baseline characteristics
Out of 41 patients with nocturnal polyuria, 17 (41,5%) were female and 24 (58,5%) were male. The mean age was 68,7(±9,1) years, the mean body mass index (BMI) was 27,5(±4,3), and the mean diastolic and systolic blood pressure were 84,2(±14,2) and 143,3(±19,7) mmHg, respectively. The mean NPi was 47,5% (±10,3) and mean episodes of nocturia were 4,2(±1,5). Thirty-four patients (83%) were diagnosed with OSA after polygraphy, of whom 12(35%), 12(35%) and 10(30%) patients had mild (AHI 5<15/hour), moderate (AHI 15<30/hour) and severe OSA (AHI≥30/hour), respectively. In seven patients (17%), no OSA was present. Of the thirty-four patients with OSA, thirty-two patients started the CPAP-trial. One patient with OSA preferred alternative treatment with mandibular reposition device (MRA). Another patient did not want a treatment because of mild symptoms. Of 32 patients who started treatment with CPAP, 26(81%) completed the 8 week treatment period, 5(16%) patients were excluded because of non-compliance, and in one case the evaluation after 8 weeks could not be carried out because of a fall of the patient (not during night time). 

Effect of treatment
After 8 weeks of compliant treatment with CPAP in 26 patients, the AHI decreased from 24.9(5.7-72.7) to 3,9 (0,9-8,7) per hour (p<0.0001). The mean NPi decreased from 47(32-69)% to 32(16-46)% (p<0.0001), and episodes of nocturia decreased from 3.7(1-5) to 1,9(0-4) (p<0.0001).

Earlier studies showed that nocturnal polyuria might be present in patients with OSA. In this study, we showed for the first time, that in patients with nocturnal polyuria, OSA is highly prevalent (83%). Patients with OSA who were treated with CPAP showed a significant decrease in AHI, NPi and episodes of nocturia.

OSA is highly prevalent in patients with nocturnal polyuria. Treatment with CPAP significantly reduces AHI, NPi and episodes of nocturia. Based on these data, we recommend urologists to refer patients with nocturnal polyuria to the pulmonologist to exclude OSA.

Bosch JL et al. The prevalence and causes of nocturia. J Urol. 2010 Aug;184(2):440-6.
D’Ancona CD et al. An International Continence Society (ICS) Report on the Terminology for Adult Male Lower Urinary Tract and Pelvic Floor Symptoms and Dysfunction. Neurourol Urodyn. 2019.
Miyazato M et al. Effect of continuous positive airway pressure on nocturnal urine production in patients with obstructive sleep apnea syndrome. Neurourol Urodyn. 2017 Feb;36(2):376-379.