Bladder outlet obstruction

Bladder outlet obstruction (BOO) has very similar presenting symptoms to what we have seen with an underactive detrusor BUT, the causes are very different.

Causes of bladder outlet obstruction

Bladder outlet obstruction is more common in older men than women (where it is commonly mis-diagnosed).

The most common cause is prostate enlargement.

Other causes include:

• Urethral stricture
• Chronic constipation/impaction which blocks/constricts the urethra
• Detrusor sphincter dyssynergia (DSD) – lack of co-ordination of the sphincter relaxation and detrusor contraction

^{Figure 3.2: Bladder outlet obstruction.}

The diagram shows an enlarged prostate, narrowing the urethra and obstructing the outflow of urine from the bladder, resulting in residual urine in the bladder after voiding.

The bladder muscle becomes thickened as the pressure increases when the muscle tries to squeeze the urine out. Overflow incontinence occurs when the bladder pressure is greater than the urethral pressure.

It causes a continuous dribbling incontinence which the person is unable to control.

Symptoms of bladder outlet obstruction

• Large post void residual urine volume
• Hesitancy
• Nocturia and daytime frequency
• Episodes of dribbling incontinence – often starting at night time first (nocturnal wetting/enuresis)
• Poor urine flow/weak stream
• Post-micturition dribbling
• Small voided volumes
• +/- urgency
• Continuous dribbling – may have continuous dribbling from overflow incontinence
• Abdominal distention – may have a feeling/awareness of abdominal distension

Clinical practice point. These symptoms are very similar to the symptoms we have looked at with a hypotonic/ underactive bladder, but as you can see the causes of these two voiding dysfunctions are very different: one is a bladder voiding dysfunction (underactive bladder) and the other is a urethral/bladder outlet obstruction.

In view of this a medical assessment is indicated to confirm diagnosis and therefore inform treatment.