New Insights into the Pathophysiology of Detrusor-Sphincter Dyssynergia

Abstract

Detrusor-sphincter dyssynergia (DSD) is a condition in which the urethral outlet actively contracts during a detrusor contraction. This is most often caused by isolated and complete suprasacral spinal cord lesions and can be manifested by external urethral sphincter (EUS) or bladder neck/ proximal urethral smooth muscle contraction, or both, reflexly generated against a hyperreflexive detrusor contraction. The resultant generation of high intravesical pressures, if left untreated, can cause damage to the bladder itself and result in ureteral reflux, hydronephrosis, and renal failure. Current therapies solve some problems but do not address the underlying pathology. Thus, understanding the pathophysiology underlying EUS DSD remains a priority in the urologic care of patients with suprasacral transverse spinal myelopathies. This review examines data and concepts from animals and humans to elucidate the pathophysiology of EUS DSD.

Contribution of the external urethral sphincter to urinary void size in unanesthetized unrestrained rats

“…Phasic EUS activity during voiding has also been reported in the mouse, hamster,cat, and non‐human primate with intact nervous systems and after damage to the nervous system in the rabbit and dog . The guinea pig EUS does not normally exhibit phasic activation during voiding, but noxious experimental conditions (e.g., instillation of slightly acidic or ice‐cold solutions into the bladder) can elicit EUS bursting. These observations, plus one anecdotal report of bursting‐like EUS activity in brain‐dead humans, support the hypothesis that bursting is a phylogenetically conserved mechanism .…”

“…The guinea pig EUS does not normally exhibit phasic activation during voiding, but noxious experimental conditions (e.g., instillation of slightly acidic or ice‐cold solutions into the bladder) can elicit EUS bursting. These observations, plus one anecdotal report of bursting‐like EUS activity in brain‐dead humans, support the hypothesis that bursting is a phylogenetically conserved mechanism . Thus, bursting may represent a primitive and/or energetically costly mode of voiding that is used differentially among mammals, and that can be recruited into action in some species when neural circuitry that controls LUT function is perturbed, e.g., by neural injury, noxious sensory input, or anesthesia.…”

“…The ubiquity of EUS bursting during voiding in anesthetized animals and the reduced void size that follows impairment of EUS activity [2][3][4][5] has led to the commonly accepted interpretation that EUS bursting is necessary for productive voiding in rats. 6 We have recently reported in a study of EUS EMG during spontaneous voiding in unanesthetized, unrestrained rats that, while bursting is the most common form of EUS EMG activity during voiding, it is not essential for voiding to occur. 7 On average, 25% of voids were not associated with EUS bursting.…”

“…In humans, the EUS is silent throughout voiding; in rats, the EUS exhibits a phasic pattern of short bursts of activity alternating with periods of silence (bursting). The ubiquity of EUS bursting during voiding in anesthetized animals and the reduced void size that follows impairment of EUS activity has led to the commonly accepted interpretation that EUS bursting is necessary for productive voiding in rats …”

External urethral sphincter motor unit recruitment patterns during micturition in the spinally intact and transected adult rat

“…This may reflect the influence of local synaptic circuits or intrinsic properties of EUS motoneurons that are active in intact rats but attenuated or absent in transected rats. rhabdosphincter; motoneuron; EUS bursting; guarding reflex; spinal cord injury THE PATTERN OF ACTIVATION of the external urethral sphincter (EUS) during micturition in the adult rat is well established (de Groat et al 1998;Fraser 2011;Kruse et al 1993;Maggi et al 1986;Mersdorf et al 1993;Streng et al 2004;Van Asselt et al 1995) and consists of three distinct phases. 1) Prior to voiding, passive filling and active contraction of the bladder result in tonic activation of the EUS muscle (i.e., the guarding reflex) that increases with bladder pressure and functions to maintain continence.…”