In the case of a flaccid (areflexic) bladder, loss of detrusor muscle tone (contractility) compromises bladder emptying and urinary retention and increases infection risk due to urine stasis. This is referred to as LMN bladder dysfunction and is typical of lesions to the conus medullaris and/or cauda equina (sacral nerve roots). External sphincter tone also tends to be flaccid, which can cause incontinence with maneuvers that increase intraabdominal pressure such as a Valsalva maneuver, application of external pressure to the bladder (Crede maneuver), straining during transfers, coughing, and sneezing. Internal sphincter tone may, however, be intact due to the higher origin of sympathetic innervation to the bladder. This may contribute to incomplete emptying, even with externally applied suprapubic pressure.
Compared to overactivity with DSD, individuals with detrusor underactivity comprise a much smaller proportion of the SCI population. It is predominantly seen in conus medullaris and/or cauda equina syndromes, and there is very little literature examining the effectiveness of interventions for this specific subpopulation. In addition, the existing evidence includes studies that address both bladder underactivity and overactivity. Conversely, the current literature more commonly addresses detrusor overactivity with DSD.