High prevalence rate of urinary incontincence(UI) in patients with Prader-Willi Syndrome (PWS) has been reported. Previous studies used parental questionnaire to assess the severity of incontinence. Until now, there is no study using objective tools to evaluate LUTD in patients with PWS. This is the first study aiming to evaluate LUTD with noninvasive tools such as uroflowmetry and post-void residual volume (PVR) in children, adolescents, and young adults with PWS.

From 2016 to 2017, we retrospectively evaluated 37 PWS patients with/without low urinary tract symptoms from our hospital. This study was approved by the Institutional Review Board. We recorded the patients’ demographic data including age, gender, height (centimeters) and weight (kilograms), IQ, presence of LUTS. Peak flow rate (Qmax), voided volume (VV), post-void residual volume (PVR), and bladder capacity were also reviewed from electronic medical records. Body mass index (BMI; kilograms per square meter) was calculated from the height and weight measures. Uroflowmetry was performed in 36 patients. In addition, 20 patients underwent post-void residual urine (PVR) measurement by transabdominal ultrasound. LUTD is defined as abnormal uroflow patterns, low peak flow rate (Qmax) or elevated PVR by age. Videourodynamic study (VUDS) was performed in selected cases.

Mean and Median age of the patients were 17.7 ± 7.8 years and 16 years. Male to female ratio was 15/22. Two patients were excluded from the following analysis because of voided volume ≤ 50ml. Of the remaining 34 uroflowmetry examination, normal voiding pattern (bell shape) was observed in 22 (64.7%) patients. Abnormal uroflowmetry pattern were obstructive in 6 (17.6%), staccato in 3 (8.8%), intermittent in 2 (5.8%), tower in 1 (2.9%), and plateau in 0 patients. Ten (29.4%) patients had a Qmax < 15ml/s. Of 20 patients undergoing PVR tests 10 (50%) had elevated PVR by age (> 6% of estimated bladder volume). In all, 17/34 (50.0 %) PWS patients had at least one abnormality of the noninvasive tests. Of the 3 cases undergoing VUDS all showed detrusor sphincter dyssynergia.

The 37 patients were classified into 2 subgroups: with and without lower LUTS (10 and 27 patients, respectively). Recorded LUTSs were frequency, urgency, urinary incontinence, nocturnal enuresis, and difficulty in voiding. Seven (18.9%) of 37 PWS subjects had UI. Though not statistically significant, PWS patients with LUTS had higher BMI, and lower IQ than those without LUTS. Peak flow rate and bladder capacity were statistically lower in symptomatic than non-symptomatic PWS patients. Rate of non-bell shaped uroflowmetry curves was statistically higher in symptomatic than non-symptomatic group. Of the 8 PWS patients with LUTS 6 (75%) had abnormal flow pattern (3 obstructive, 2 staccato, and 1 intermittent), and 6 (75%) had a peak flow rate <15.0 ml/s.

From the results we found high prevalence rate of LUTD from the PWS patients. Fifty percent of PWS patients with/without LUTS had LUTD. The pathophysiology of DSD in PWS patients is still unclear. Intellectual disability, obesity, or autonomic dysfunction may play a role, but the true mechanism needs further investigation.

Half of PWS patients with/without LUTS had LUTD. Non-invasive study such as uroflowmetry and post-void residual urine by ultrasound is recommended to all PWS patients.

Von Gontard A, Didden R, Sinnema M, et al. Urinary incontinence in persons with Prader-Willi Syndrome. BJU Int. 2010;106:1758.
Equit M, Piro-Hussong A, Niemczyk J, et al. Elimination disorders in persons with Prader-Willi and Fragile-X syndromes. Neurourol Urodyn. 2013;32:986