Evaluation of the occurrence and diagnose definitions for nocturnal polyuria in spinal cord injured patients during rehabilitation.

Background: Little is known about the occurrence of nocturnal polyuria (NP) in spinal cord injured (SCI) patients and the definitions which are preferable in this population.
Aim: To determine the occurrence of NP in SCI patients during in-patient rehabilitation in the Ghent University Hospital. To study the influence of different time periods (daytime, bed rest and sleep) on the accuracy of the existing diagnose definitions for NP specifically for this type of patients.
Design: Retrospective study using patient records.
Setting: SCI patients during hospital-based rehabilitation between 2011 and 2014.
Population: Seventy-four SCI patients were selected and their records of frequency-volume charts (FVC) were examined, after exclusion of unreliable data, forty-seven patients were retained for the current study.
Methods: Retrospective study using data from FVC of either two or three days from patients with SCI. Nocturnal urine production (NUP) and nocturnal polyuria index (NPi) were calculated.
Results: There was a significant increase in diuresis, calculated as urine production, between day time and bed rest (P=0.008) and between day time and sleep (P=0.001). All patients showed NP during a 12-hour night time period (including both bed rest and sleep) and 39 patients showed NP during the 8-hour period of sleep. There was no significant difference in mean urine production between bed rest and sleep. Prevalence of NP did not significantly differ between the complete or incomplete SCI patients or between patients with higher and lower SCI levels.
Conclusions: This study showed that the occurrence of NP in patients with SCI is high and that it is important to consider which definitions of NP are used for diagnosis. Increase in diuresis is observed during bed rest and sleep and the diagnose is correctly estimated when nocturnal urine production definitions are used in both time periods. In accordance with what was expected, diagnose of NP was overestimated when NP index type definitions were used.
Clinical Rehabilitation Impact: It is important to be aware of the frequent-occurrence of NP in SCI patients and the impact of their daily routine to the accuracy of the diagnosis of NP. More knowledge about this topic can help to avoid incontinence caused by nocturnal polyuria.