Mechanism of bladder dysfunction in idiopathic normal pressure hydrocephalus

To elucidate the mechanism of bladder dysfunction in idiopathic normal pressure hydrocephalus (iNPH) by a urodynamic study.

Forty-two patients with possible iNPH, who were diagnosed by clinical symptoms/signs (gait, cognitive, and urinary disorders) with typical imaging features (ventricular enlargement) and normal cerebrospinal fluid pressure, were enrolled. The subjects included 36 men and 6 women; mean age, 72 years (62-83 years). All patients underwent a urodynamic test according to the definitions and methods proposed by the International Continence Society.

Lower urinary tract symptoms were seen in 93% of the patients, with storage symptoms (93%) being more common than voiding symptoms (71%); and urinary urgency (overactive bladder) (64%)/frequency (64%) being more common than urinary incontinence (57%). The mean values for the maximum flow rate and post-void residual (PVR) volume were 11.7 ml/sec and 42.1 ml, respectively. PVR >100 ml was noted in six patients (three men, three women; range, 100-228 ml). Although the majority of patients had normal bladder volume at the first sensation (mean 134 ml), bladder capacity was small (mean 200 ml) and detrusor overactivity was seen in 95% of patients.

While incontinence can result secondarily from gait disturbance or dementia, detrusor overactivity mostly underlies urinary urgency/frequency and incontinence in iNPH.