How a normal bladder works

Normally, when the bladder is full, nerve signals travel from the bladder to the brain and trigger the urge to urinate. When you are in the ideal conditions for urinating, your brain instructs the main muscle in the bladder, the detrusor, to contract to pass urine. It also instructs the sphincter muscles that surround the urethra to relax so that urine can flow out.

But in the case of an overactive bladder, the difficulty in holding urine in the bladder is caused by a dysfunction of detrusor, which begins to contract as soon as a small amount of urine is stored in the bladder. This difficulty is logically accompanied by an increased frequency of urination, nocturia, urination emergencies but also sometimes urinary incontinence.

Overactive bladder is therefore a hypersensitive disorder that can cause urinary incontinence, but by no means are they synonymous^{1 2}.

There are also 2 types of overactive bladder : overactive dry bladder (emergencies without incontinence) and overactive wet bladder (emergencies with incontinence)³.

Where does overactive bladder come from?

The pathophysiology of overactive bladder is very poorly understood. We just know that it is due to neurogenic and myogenic factors⁴, impaired sensory pathways in the bladder, dysfunction of the urothelium and signal mechanisms⁵, and abnormalities in the conduction of these signals to the brain. 

The lower urinary tract includes both the bladder and the richly innervated urethra. Their major function is to store urine in the bladder and to evacuate it periodically and at appropriate times. The neural circuit that controls this process is complex: it involves pathways at different levels of the brain, spinal cord and peripheral nervous system and is modulated by many neurotransmitters. All this explains why overactive bladder reaches a high prevalence in neurological diseases.

Bladder filling

During bladder filling, the parasympathetic function of the detrusor is inhibited, resulting in sagging bladder with simultaneous contractions of the urethral sphincters (to prevent involuntary emptying). This first step is accomplished by norepinephrine which acts on special detrusor receptors, beta3-adrenoreceptors.

Bladder evacuation

When the volume of the bladder reaches the threshold for voiding, the bladder contracts, the urethra relaxes, which logically leads to emptying. The sensations of bladder overflow are transmitted to the spinal cord by various nerves, pelvic and hypogastric. This is mainly accomplished through the release of the excitatory neurotransmitter acetylcholine.

The maintenance and alternation of these cycles involves complex interactions that are still very little understood.

What are the diseases and conditions linked to overactive bladder?

It has been observed that aging, Parkinson’s disease, interstitial cystitis, stress, depression, type 2 diabetes, obstruction to the outflow of the bladder, spinal cord injury, head trauma, stroke. -cerebral was involved in the occurrence of an overactive bladder.

Aging. Overactive bladder is one of the most common causes of urinary incontinence in older people. This is why we often confuse them both. This is believed to be due to weaker signals in the brain causing bladder control. We are gradually witnessing a denervation of the bladder, associated with disturbances in the release of various neurotransmitters.

Diabetes. People with diabetes who do not receive adequate treatment are at risk of experiencing various symptoms related to overactive bladder such as nocturia, problems with fully evacuating the bladder, and incontinence.

Obstruction to the bladder outflow. Rarer in women than in men, such an obstruction is usually the consequence of benign prostatic hyperplasia.

Spinal cord injuries. This type of injury leads to bladder dysfunction, ranging from urinary incontinence to complete loss of the ability to empty the bladder.

Cerebrovascular accident. People who have experienced a stroke or head trauma frequently experience problems with an overactive bladder.

Parkinson disease. The more the disease progresses, the more dysfunctions of the urinary tract appear: emergencies, nocturia, urgency incontinence^{16 17}.

Various. Other conditions such as interstitial cystitis, stress and depression are believed to be linked to overactive bladder.

Overactive bladder in numbers

An overactive bladder is manifested by frequent urination (between 7 and 20 times a day and at night), which may be accompanied by urine leakage due to the urge to urinate.

The prevalence of overactive bladder would reach around 17% but would be more marked after the age of 64 years. About 67% of people with an overactive bladder do not experience a leak (overactive dry bladder). Nevertheless, some of them would live with the same fear of not being able to hold back, which poses some problems of definition: from when can we really speak of overactive wet bladder?