Overactive bladder (OAB) is defined as "urgency, with or without urge incontinence, usually with frequency and nocturia" in the absence of local pathological or endocrine factors. Urgency is defined as "the complaint of a sudden compelling desire to pass urine that is difficult to defer" and an abnormal sensation that is distinctly different from the normal physiologic feeling of 'urge to void' that occurs during typical bladder-filling cycles.