P. P. Smith, L. A. Birder, P. Abrams, A. J. Wein and C. R. Chapple

Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/26872574

It seems like “underactive bladder” (UAB) and “detrusor underactivity” (DU) are 2 buzzwords that will constitute the focus of a subject that will be the point of discussion by those interested in lower urinary tract dysfunction for at least the next few years. The relationship of symptoms, function and cause constitutes the focus of this report resulting from a 2014 International Consultation on Incontinence-Research Society Think Tank titled, “Does detrusor underactivity exist, and if so is it neurogenic, myogenic, or both?” Although publication has obviously been delayed, the summary is still quite contemporary regarding the problems and pitfalls inherent in the definitions, diagnosis and therapy of the conditions encompassed by these 2 terms. Equating UAB with DU and impaired contractility is attempting simplification, which unfortunately leads only to confusion. The terms are not interchangeable.

Although proposals for improving terminology have emerged since this think tank, the authors provide a very good introduction to the conceptual overlap of symptoms (underactive bladder), function (detrusor underactivity) and etiology, and how the overlap of these circles may vary across subpopulations and within individuals as a consequence of disease and aging. Detrusor underactivity is a description of objective inadequacy of voiding, and, therefore, a measure of function and not etiology. A formal accepted definition of DU is lacking, and any such definition is relative to normal voiding characteristics and limited by an incomplete phenotyping of voiding in specific populations (ie based on age and gender).

The authors describe “impaired contractility” as indicating an inherent muscular failure to generate an adequate output in the presence of sufficient metabolic substrate and normal levels of neurological stimulation. They propose that “detrusor underactivity” should be preserved for urodynamic findings as described in the original International Continence Society definition, the problem being, of course, that no one knows what constitutes a contraction of reduced strength and/or duration, a normal time span or complete bladder emptying. The authors propose that “according to an integrative hypothesis, detrusor underactivity is a relative functional threshold deficiency resulting from failure of biological adaptation to multiple systemic failures.” They propose that “underactive bladder” should be reserved for the symptom complex of prolonged urination, with or without a sensation of incomplete bladder emptying, usually with hesitancy in a slow stream. This term should not be taken to imply a specific pathology or etiology and may or may not constitute an accurate perception of detrusor underactivity. However, that is to formally be finally defined. As the authors suggested at that think tank, focus groups are now trying to define what amounts to a symptom complex of underactive bladder and how this relates to clinically observed dysfunction (detrusor underactivity). However, that is to be defined in age specific and gender specific populations.

Although this summary is not the “last word” in contemporary discussions of the concepts of UAB, DU or impaired contractility, it is good background information for anyone interested in the subject with reference to the difficulties that arise when trying to define these entities. The “elephant in the room,” ie successful therapy or the lack of successful therapy, is left to subsequent discussions.

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