We gain bladder control as young children and from this time onwards a healthy bladder is controlled by the central nervous system. The detrusor will not normally contract until it is convenient to initiate a void. This contraction is initiated at the level of the cerebral cortex. When detrusor overactivity is present, however, the detrusor contracts spontaneously during the filling phase of the micturition cycle, when micturition would normally be inhibited. The true incidence of this condition is unknown; it is possible that we all exhibit detrusor overactivity on occasions. For example, many ‘healthy’ people will have symptoms of urinary urgency when the weather is cold, when they have drunk strong coffee or when they put their key in the front door with a full bladder. In some people, this condition causes great distress and can manifest as severe urinary frequency with urgency. There may be associated urge urinary incontinence; this can be particularly distressing as the bladder may empty completely off an unstable detrusor contraction.
Definition and aetiology
Detrusor overactivity is defined as a urodynamic observation characterised by involuntary detrusor contractions during the filling phase that may be spontaneous or provoked. It is apparent from this definition that, as there has to be objective evidence of a detrusor contraction, detrusor overactivity can be diagnosed only after a urodynamic study. It is neither necessary nor desirable to investigate all women presenting with symptoms of frequency, urgency and urge incontinence with a urodynamic study. When the history is typical, one can usually presume that there is underlying detrusor overactivity and treat empirically for 1–2 months. Urodynamics can be reserved for those in whom empirical treatment fails.