Neurourology and Urodynamics 26:904–907 (2007) REVIEW ARTICLE Defining Overactive Bladder as Hypersensitivity Osamu Yamaguchi, 1 * Kazuya Honda, 1 Masanori Nomiya, 1 Keiichi Shishido, 1 Hidehiro Kakizaki, 2 Hiroshi Tanaka, 3 Tomonori Yamanishi, 4 Yukio Homma, 5 Masayuki Takeda, 6 Isao Araki, 6 Kenji Obara, 7 Osamu Nishizawa, 8 Yasuhiko Igawa, 8 Momokazu Goto, 9 Osamu Yokoyama, 10 Narihito Seki, 11 Mineo Takei, 12 and Masaki Yoshida 13 1 Department of Urology, Fukushima Medical University, Fukushima, Japan 2 Asahikawa Medical College, Asahikawa, Japan 3 Hokkaido University, Sapporo, Japan 4 Dokkyo University, Tochigi, Japan 5 Japan Red Cross Medical Center, Tokyo, Japan 6 University of Yamanashi, Yamanashi, Japan 7 Niigata University, Niigata, Japan 8 Shinshu University, Mastumoto, Japan 9 Nagoya University, Nagoya, Japan 10 University of Fukui, Fukui, Japan 11 Kyusyu University, Fukuoka, Japan 12 Harasanshin Hospital, Fukuoka, Japan 13 Kumamoto University, Kumamoto, Japan 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. Neurourol. Urodynam. 26:904–907, 2007. ß 2007 Wiley-Liss, Inc. Key words: maximum bladder volume; micturition behavior; urge; urgency INTRODUCTION Overactive bladder (OAB) has been recently defined by the International Continence Society (ICS) as urgency, with or without urgency incontinence, usually with frequency and nocturia, in the absence of infection or other obvious pathology. 1 Based on two major epidemiologic studies in Europe and the United States, an estimated 17% of the general adult population experience OAB. 2,3 Notably, data from both studies indicate that the majority of patients with OAB (64%) do not actually experience urgency incontinence. Urgency, an essential component for a diagnosis of OAB, is defined by the ICS as a sudden, compelling, difficult-to-defer desire to pass urine. 1 According to this definition, it is the cornerstone symptom that drives the other symptoms of OAB (i.e., frequency, nocturia, and urgency incontinence). 4 Urgency, with or without urgency incontinence, has been shown to have a greater impact on quality of life than incontinence, frequency, or nocturia. 5 The ICS definition of urgency assumes an abnormal or pathologic bladder sensation that is distinguishable from the normal physiologic sensation of urge to void during a normal bladder-filling cycle. 4,6 The latter is characterized by a pattern of sensations or desire to void that increases in intensity with increasing bladder volume, resulting in normal, controlled, Karl-Erik Andersson led the review process. *Correspondence to: Osamu Yamaguchi, MD, PhD, Department of Urology, Fukushima Medical University, 1 Hikariga-oka, Fukushima City, Fukushima prefecture 960-1295, Japan. E-mail: yamaosa@fmu.ac.jp Received 28 March 2007; Accepted 1 June 2007 Published online 30 July 2007 in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/nau.20482 ß 2007 Wiley-Liss, Inc.