Definition: Involuntary loss of urine triggered by any increase in intra-abdominal pressure — without a detrusor contraction.

Pathophysiology: The urethral closure pressure fails to exceed the intra-abdominal pressure spike. Two mechanisms:

• Urethral hypermobility — weakened pelvic floor “hammock” allows the bladder neck to descend and open under pressure (commonest cause in women, especially post-partum)
• Intrinsic sphincter deficiency (ISD) — the urethral sphincter itself is weakened or damaged (post-surgical, post-radiation, post-PFUI)

Classic patient: Multiparous woman; post-radical prostatectomy male.
Small volume leakage — spurts, not floods.

Definition: Moderate-to-large volume leakage immediately following a sudden, irrepressible urge to void that cannot be deferred.

Pathophysiology: Detrusor overactivity — uninhibited, involuntary smooth muscle contractions during the filling phase. Causes:

• Idiopathic (most common)
• Neurogenic — MS, stroke, Parkinson’s disease, spinal cord injury
• Local irritants — UTI, bladder stones, carcinoma in situ

Sensory triggers: Running water, cold air, putting key in the front door (“latchkey incontinence”).
Large volume leakage — floods before reaching the toilet.

Definition: Constant or frequent dribbling from a chronically distended, overfull bladder that cannot empty properly.

Pathophysiology: Two mechanisms:

• Bladder outlet obstruction (BOO) — BPH (most common in men), urethral stricture, pelvic mass. Bladder fills faster than it can empty → overdistension
• Atonic / underactive detrusor — diabetic neuropathy (autonomic), spinal cord injury (LMN lesion), cauda equina syndrome, anticholinergic drugs

Key feature: Large post-void residual (PVR) on bladder scan or catheterisation.
Can present as recurrent UTIs — stagnant urine is a bacterial reservoir.

Definition: Involuntary leakage where the lower urinary tract is entirely intact — the problem is the patient’s inability to access the toilet.

Pathophysiology:

• Physical impairment — severe arthritis, Parkinson’s rigidity, post-stroke immobility, frailty
• Cognitive impairment — dementia, delirium (fails to recognise the urge or find the toilet)
• Environmental barriers — distance to toilet, poor lighting, bedrails

Management priority: Address the functional barrier — mobility aids, scheduled voiding, environmental modification, carer support. No lower urinary tract treatment needed.