Defining overactive bladder as hypersensitivity

Overactive bladder (OAB), according to the International Continence Society (ICS) definition, is a symptom syndrome, with urgency as the cornerstone symptom. However, the word 'urgency' and its definition continue to be the subject of much debate and confusion. It is generally difficult for patients to differentiate urgency from normal urge, particularly when the desire to void is strong. To investigate the micturition behavior associated with OAB, we conducted a Patient Trust Study in 21 intelligent (i.e., to be 'trusted') female patients who could clearly and accurately discriminate between urgency and urge. The results showed that in 43% of patients seeking medical care, urgency episodes occurred less than once/day, and some patients had days without urgency. Our patients deferred voiding until bladder sensation was relatively strong, suggesting that coping was not common among these patients. Four of the 21 patients studied experienced spontaneous resolution of several urgency episodes. At volumes exceeding 40% of the maximum bladder volume (MBV), urgency episodes occurred frequently and independently of the bladder volume, indicating that 40% of the MBV may be a threshold of bladder volume to induce urgency. A linear relationship was observed between bladder volume and increasing bladder sensation. However, compared with normal subjects, urge sensation increased markedly at any given bladder volume among patients with OAB in our study. This hypersensitivity was observed in our patients regardless of urgency episodes. We therefore hypothesized that OAB may be more accurately defined as a hypersensitivity disorder rather than a syndrome characterized by urgency.