Urinary Incontinence – Part 2
Heidi K. Wennemer, D.O.
Neurogenic bladder is a broad term that is defined as malfunctioning urinary bladder due to neurologic dysfunction or insult emanating from internal or external trauma, disease, or injury.
The symptoms of neurogenic bladder range from detrusor (bladder) under activity to overactivity depending on the site of neurologic insult. In addition, the urinary sphincter may be affected, resulting in loss of coordination between relaxation of the urethral sphincter and detrusor contraction called detrusor sphincter dyssynergia (DSD).
These patients often require intermittent catheterization, Foley catheter, suprapubic tube, or sphincterotomy with external catheter for adequate bladder drainage. The primary goal with these patients is to keep bladder pressures low, because high bladder pressures can be transmitted to the kidneys.
To further discuss neurogenic bladder, one must have a basic understanding of normal voiding and anatomy. Coordinated voiding requires that the detrusor contract at the same time as the urethral sphincter relax. In patients with DSD, coordinated voiding does not occur.
Central Nervous System
There are three areas of the central nervous system (CNS) that control bladder function: the sacral micturition center, the pontine micturition center, and the cerebral cortex. The sacral micturition center is located in the spinal cord at the sacral (S2-S4) levels and is responsible for bladder contraction. The pontine micturition center is located in the brainstem (pons) and appears to play a role in coordinating relaxation of the external sphincter with bladder contractions. The cerebral cortex plays inhibits the an inhibitory role in relation to the sacral micturition center.
Sympathetic nerve fibers travel from the spinal cord (levels T11-L2) to the bladder. These fibers maintain relaxation of the bladder for urine storage.
Parasympathetic nerve impulses travel from sacral spinal cord levels (S2-S4) to the bladder wall where they produce bladder contraction and sphincter relaxation to allow voiding.
In addition to the internal sphincter, there is also an external urethral sphincter that is under voluntary control and is innervated by nerves originating in the sacral spinal cord (S2-S4). This sphincter normally contracts in response to coughing, Valsalva maneuver, or when a person actively tries to prevent the flow of urine.
Types of Neurogenic Bladder
We will now review the various types of neurogenic bladder by the location of injury to the central nervous system.
Lesions above the pontine micturition center lead to lack of inhibition from the cerebral cortex and result in uninhibited bladder contractions, but voluntary relaxation of the urethral sphincter remains intact. This is also referred to as an uninhibited bladder, or reflex bladder. In this case the bladder fills slowly with urine and reflexively empties when it is full. The patient has no sensation or control over his or her bladder function. This problem is encountered commonly in patients with Stroke, Traumatic Brain Injury (TBI), or dementia.
Spinal Cord Lesion
Lesions of the spinal cord or brainstem below the pontine micturition center and above the sacral micturition center lead to uninhibited bladder contractions with uncoordinated sphincter activity. This is also called an upper motor neuron bladder. The bladder volumes are small, the bladder is contracted, and intravesicular pressures are high. In addition, there is often detrusor sphincter dyssynergia. The external sphincter may contract when the bladder contracts. This effectively causes outlet obstruction and even higher bladder pressures which may cause damage to the kidneys.
Cauda Equina Syndrome
Lesions of the sacral micturition center in the sacral spinal cord (S2-4) cause detrusor areflexia. This leads to a low tone, distended bladder, and overflow incontinence. This is also called a lower motor neuron bladder.
Peripheral nerve injury
Similar to injury to the sacral cord, individuals with lesions of the peripheral nerves to the bladder, will have low tone bladders. Diabetes mellitus and AIDS are 2 of the conditions causing peripheral neuropathy resulting in urinary retention. These diseases destroy the nerves to the bladder and may lead to silent, painless distention of the bladder. Patients with chronic diabetes lose the sensation of bladder filling first, before the bladder decompensates. Other diseases causing lower motor neuron bladder due to peripheral nerve injury are poliomyelitis, Guillain-Barré syndrome, severe genital herpes, pernicious anemia, and neurosyphilis (tabes dorsalis).
Neurogenic bladder is a malfunctioning bladder due to any type of neurologic disorder.
Detrusor is the muscle of the bladder wall. Contraction of this muscle causes bladder contraction and voiding.
Detrusor hyperreflexia refers to overactive bladder symptoms due to a suprapontine (above the pontine micturition center) upper motor neuron neurologic disorder. The external sphincter functions normally. The detrusor muscle and the external sphincter are coordinated.
Detrusor sphincter dyssynergia with detrusor hyperreflexia (DSD-DH) refers to overactive bladder symptoms due to neurologic upper motor neuron disorder of the suprasacral spinal cord (above the sacralmicturition center). The patient is in urinaryretention because both the detrusor and the sphincter are contracting at the same time; they are not coordinated.
Detrusor hyperreflexia with impaired contractility (DHIC) refers to overactive bladder symptoms, but the detrusor cannot generate enough pressure to allow complete emptying. The external sphincter is in synergy with detrusor contraction, but the detrusor is too weak for proper voiding to occur.
Urinary retention is the inability of the urinary bladder to empty. The cause may be neurologic or non-neurologic.
Detrusor instability refers to overactive bladder symptoms without neurologic impairment. External sphincter functions normally, in synergy.
Detrusor areflexia is complete inability of the detrusor to empty due to a lower motor neuron lesion (such as a sacral cord lesion or peripheral nerve lesion).