A commonly used classification scheme used by urologists and rehabilitation specialists, described by Wein, classifies bladder impairment following spinal cord injury according to the level of injury:
suprasacral (infrapontine) bladder - upper motor neuron lesion, releasing the sacral micturition center from descending inhibition. This results in:
- detrusor hyperreflexia/overactivity
- detrusor-external sphincter dyssynergia (DESD), referring to inappropriate co-contraction of the external urethral sphincter (EUS) with voiding detrusor contraction, increases the risk of reflux nephropathy
- mixed neurogenic bladder (Type A) - a lesion in the conus medullaris with resulting injury to the sacral micturition center causing detrusor hyporeflexia (under-activity) with external sphincter hyperreflexia with large bladder volumes and overflow incontinence.
- mixed neurogenic bladder (Type B) - a lesion involving the pudendal nucleus causing detrusor hyperreflexia with external sphincter hypotonia. This is associated with small bladder volumes, frequency and incontinence.
infrasacral bladder - lower motor neuron lesion involving the conus medullaris or cauda equina resulting in:
- detrusor areflexia and areflexia with atonia of the pelvic floor muscles
- may have isolated increase in bladder neck/internal sphincter resistance due to intact sympathetic supply (arising from T11-L2)
- non-contractile bladder with urinary leakage from overflow incontinence (this may also occur due to recurrent bladder over-distension)
It must be noted that different underlying impairments may lead to a similar outward appearance of bladder dysfunction. For example, detrusor overactivity (hyperreflexia), poor bladder compliance (with increased resistance to filling) or bladder neck insufficiency all can cause storage failure. Similarly, detrusor-sphincter dyssynergia, a non-contractile bladder, myogenic detrusor insufficiency from chronic over-distension or mechanical obstruction (due to benign prostatic hypertrophy, pelvic malignancy or urethral stricture) may lead to voiding failure.