The Epidemiology and Pathophysiology of Neurogenic Bladder

Neurogenic bladder is a disorder of the lower urinary tract created by damage to or diseases of the nervous system. Found in many patients with neurologic disorders, including multiple sclerosis, Parkinson’s disease, spinal cord injury, and spina bifida among others, neurogenic bladder can lead to problematic symptoms and complications including urinary incontinence, frequency, and urgency, along with risk for infection and involvement of the upper urinary tract and kidney disease. The disorder can also create substantial embarrassment resulting in social isolation for affected patients. Healthcare utilization may be excessive in patients with neurogenic bladder, including office and emergency department visits and subsequent hospitalizations. Because of its significant effects on quality of life, it is important to reassess the epidemiology and physiology of neurogenic bladder, its diagnosis and assessment, and the impact of the symptoms and complications associated with it to better manage patients with this disorder and improve outcomes.

(Am J Manag Care. 2013;19:S191-S196)Neurogenic Bladder: An Introduction

Normal micturition (urination) requires proper function of both the bladder and the urethra, including normal compliance within the bladder detrusor muscle and a physiologically competent urinary sphincter. The process of micturition is controlled by the central nervous system (CNS), which coordinates sympathetic, parasympathetic, and somatic nervous system activity for normal micturition and urinary continence. Dysfunction in voiding can result from mechanical or physiologic abnormalities in the urinary tract that lead to an inability of the sphincter to appropriately increase or decrease its pressure when bladder pressure is increased. Damage to or diseases of the CNS or within the peripheral or autonomic nervous system may lead to neurogenic bladder (NGB) dysfunction. NGB dysfunction may arise as a result of several neurologic conditions. NGB has been found in 40% to 90% of patients in the United States with multiple sclerosis (MS), 37% to 72% of patients with parkinsonism, and 15% of patients with stroke.^1,2 It is estimated that 70% to 84% of patients with spinal cord injuries have at least some degree of bladder dysfunction.^1,3 Bladder dysfunction is also frequently seen in patients with spina bifida, with vesicoureteral reflux present in up to 40% of children affected by 5 years of age and with up to 60.9% of young adults with spina bifida experiencing urinary incontinence.^1,4 Less common scenarios for NGB may include diabetes mellitus with autonomic neuropathy, unintended sequelae following pelvic surgery, and cauda equina syndrome resulting from lumbar spine pathology.¹ Many patients with NGB, especially those with multiple sclerosis, cerebrovascular accidents, and spinal cord injury, experience uninhibited bladder contractions.^1,5 Bothersome urinary symptoms associated with NGB include urinary incontinence (UI), frequency, and urgency.⁵ Patients also may have increased risk and incidence of urinary tract infections (UTIs) and bladder outlet obstruction. If not treated optimally, patients with NGB may also be at risk for sepsis and renal failure, and these patients have higher numbers of clinical office and ED visits annually, with up to one-third of these visits leading to a need for hospitalization.^1,3 In addition to the physical and clinical burden associated with NGB, the associated urinary incontinence can negatively impact a patient’s quality of life, causing embarrassment, depression, and social isolation.^1,6 As diagnostic and treatment options continue to advance for patients with NGB, it is important to reassess its epidemiology and physiology, diagnosis, assessment, and classification, and the impact of the symptoms and complications associated with NGB on the patients affected by this disorder.

Neurologic Disorders and Neurogenic BladderMultiple Sclerosis

Normal urinary tract function is dependent on neural integration between the central and peripheral nervous systems.⁷ MS, the most common neuroinflammatory disorder of the CNS, may cause lower urinary tract dysfunction and NGB as a result of a disruption of this integration. Urinary symptoms in MS are likely caused by neural demyelization and axonal degradation, and patients with MS lesions in specific CNS regions (encephalic, spinal suprasacral regions) may be more likely to experience major urinary symptoms.^7,8 It has also been hypothesized that CNS lesions from MS may exert a local effect on bladder function.⁸ A variety of patterns may be seen, with detrusor overactivity of the bladder noted in 50% to 90% of patients with MS and detrusor areflexia in 20% to 30% of patients with MS.^1,3 Neurogenic lower urinary tract dysfunction is often noted during the first 10 years following MS diagnosis and tends to increase as the patient’s level of disability worsens.^7,9 This urinary tract dysfunction can lead to substantial limitations in daily activity for patients with MS.⁷ More than 80% of patients with MS report genitourinary symptoms, with voiding dysfunction impacting the vast majority of these patients.^9,10 In addition, bladder symptoms are frequently mismanaged in patients with MS, often leading to urinary retention and/or subsequent UTI.¹¹ Early and accurate assessment of potential lower urinary tract dysfunction is essential to protect the upper urinary tract, optimize management, and improve quality of life for these patients.⁷

Idiopathic Parkinson’s Disease

Idiopathic Parkinson’s disease (IPD) presents as an extrapyramidal neurologic syndrome, most commonly associated with prominent motor symptoms. However, non-motor symptoms have been recognized in parkinsonism, and urinary symptoms are frequently present in these patients.¹² Urinary dysfunction as a manifestation of autonomic failure is common in patients with IPD.¹³ Studies have shown that urinary storage symptoms (frequency, urgency, urge urinary incontinence) are present in 57% to 83% of patients with IPD, and voiding symptoms (poor force of stream, hesitancy, incomplete emptying) are seen in 17% to 27% of this patient population.¹² For most patients, the onset of bladder dysfunction occurs after motor symptoms are evident, and voiding dysfunction tends to increase with neurologic impairment as opposed to disease duration.¹⁴ As with NGB associated with other disorders, a patient’s renal function and long-term health may be compromised if urinary dysfunction in IPD is not recognized and addressed promptly. One confounding factor impacting correct diagnosis and management is the potential for clinicians to confuse patients with pure IPD with those who have multiple symptom atrophy, a disorder that manifests with parkinsonian-like motor symptoms but with substantial differences in both neurologic progression and urinary disturbances.^12,14 Bladder symptoms may also be the result of coexistant disease processes such as UTI, diabetes, or in men, benign prostatic hypertrophy, which can complicate accurate diagnosis. Appropriate diagnosis is key to management of urinary dysfunction in IPD, and a multidisciplinary approach may be needed for symptom management and optimal patient quality of life.¹⁴

The primary urinary complaints in patients with urinary dysfunction due to IPD include urgency, frequency, UI, and nocturia. This is likely due to the urodynamic finding of detrusor overactivity, which may be seen in 45% to 93% of patients with IPD.¹² UI in patients with IPD may be of multifactorial origin; not only do the patients have significant bladder dysfunction, but there also are functional problems such as impaired mobility and poor manual dexterity, which can impact the patient’s ability to perform appropriate toileting. Some patients with IPD also experience sleep disturbances and nocturnal polyuria. Management of these patients must take into consideration how IPD influences the lower urinary tract as well the possible pharmacologic effects of anti-parkinsonian agents the patient may be taking.¹⁴

Spinal Cord Injury

It is estimated that there are more than 200,000 patients with traumatic spinal cord injury (SCI) in the United States, with an incidence of approximately 12,000 new cases estimated annually.¹⁵ Urinary dysfunction is very common in these individuals; approximately 81% of patients with SCI report at least some degree of impaired bladder function within 1 year after injury.^16,17 The expected level of bladder dysfunction may potentially be determined by the spinal level at which the SCI occurred. Injury proximal to the sacral spinal cord should lead to an upper motor neuron lesion and detrusor overactivity. Injuries that involve the sacral spinal cord or cauda equina should result in a lower motor neuron lesion and detrusor areflexia. Both of these classifications assume the presence of a complete neurologic lesion; however, the presence of a complete lesion may be variable. In addition, patients with a suprasacral SCI are at risk for detrusor-external sphincter dyssynergia, which can place the patient at risk for incomplete bladder emptying and elevated bladder pressures.^1,18 Many patients with SCI do not have well-defined complete lesions, and although the majority of patients demonstrate fairly consistent bladder and sphincter behavior based on neurologic deficit, this is not definitive for all patients with SCI. Thorough urodynamic evaluation to evaluate bladder and sphincter behavior needs to be performed to better assess urinary dysfunction prior to initiation of therapy.¹⁸ Management of NGB dysfunction is a critical component of a rehabilitation program for a patient with SCI, as NGB contributes significantly to the overall morbidity of these patients. Losing normal bladder function is disabling and may lead to urinary tract deterioration, urinary incontinence, and reduced quality of life. Principal goals for management are preservation of renal function, improved continence, and reduction of urinary complications such as kidney stones and UTI. Bladder management focuses on therapy to facilitate bladder filling and storage of urine and treatment to facilitate bladder emptying that assists in preserving both renal function and social functioning to allow patients to enjoy a healthier life.¹⁶

Spina Bifida

Spina bifida is a common neurologic abnormality, with worldwide incidence estimated at 0.3 to 4.5 per 1000 births.¹⁹ Whereas barely 10% of these patients survived infancy prior to 1960, most patients today have a normal expected lifespan. This extended life expectancy also now means that many patients with this disease and complex disabilities survive well into adulthood with increasing expectations of life.⁴ The disorder is associated with prenatal folate deficiency, and with government-mandated folate supplementation in foods in the United States, the incidence of spina bifida has been decreasing.²⁰ UI is a common symptom related to NGB in patients with spina bifida, and possible urodynamic findings include detrusor overactivity, poor bladder compliance, and a fixed, obstructing outlet that may be incompetent as well. NGB secondary to spina bifida may result in a high-pressure bladder, which places the patient at risk of upper urinary tract damage.^19,20 The primary goal for therapy is to convert the bladder into a low-pressure reservoir and protect the upper urinary tract. Preservation of renal function is key in the management of urinary dysfunction related to spina bifida.¹⁹ Adjustments in patient management must be made as the patient grows and progresses into adolescence and adulthood to allow the patient independence with respect to bladder management.¹⁹ Successful treatment of UI related to spina bifida can be complex and will continue into adulthood.²⁰ In 1 study, UI was found in nearly 61% of young adults with the disorder. Bladder management techniques must be individualized in patients with spina bifida to preserve both renal function and quality of life.^4,20

Diagnosis and Assessment of Neurogenic Bladder

Normal and Abnormal Neurophysiology of the Lower Urinary Tract

It is important to consider the neuroanatomy and neurophysiology of the upper and lower urinary tracts in the assessment and management of patients with NGB. The lower urinary tract, composed of the bladder and urethra, performs 2 main functions, namely the storage of urine at low pressures without leakage and the voiding of urine at appropriate intervals. These functions are controlled by complex mechanisms involving all levels of the nervous system.^1,21 The storage phase encompasses the vast majority of the time in healthy bladders and is maintained by inhibition of parasympathetic activity and active relaxation of the detrusor muscle. Sympathetic and pudendal nerve—mediated contraction of the urethral sphincters prevents urine leakage under normal conditions. Disruption of the bladder storage phase leads to bothersome symptoms, including urinary frequency, urgency, and urge incontinence.^21,22 During voiding, sensory information from the bladder triggers the micturition reflex. Inhibition of the pudendal nerve and suppression of sympathetic activity result in detrusor muscle contraction and relaxation within the pelvic floor muscles and the urethral sphincters. Three voiding centers control the function of the bladder: the sacral micturition center, the pontine micturition center, and the cerebral cortex.^21-23 The sacral micturition center is located at the spinal sacral S2 to S4 levels and controls bladder contraction. This area is a reflex center where afferent impulses from the bladder signal bladder fullness and efferent parasympathetic impulses to the bladder result in bladder contraction. The pontine micturition center is found in the brain stem and coordinates relaxation of the external sphincter to synchronize with bladder contractions. The cerebral cortex exerts final control on the bladder processes as the detrusor center in this region directs micturition centers to either begin or delay voiding, depending on the particular situation the patient is in at the time.²¹

Many different neurologic disorders can create lower urinary tract dysfunction through the development of lesions in different nerve centers. For example, MS tends to attack the suprasacral region, whereas stroke and Parkinson’s disease affect the suprapontine area. Lesions in peripheral nerves or the sacral micturition center can lead to detrusor areflexia, in which a patient may experience no urge to urinate, leading to bladder distention and overflow incontinence. Brain stem or spinal cord damage between the sacral and pontine micturition centers results in neurogenic detrusor overactivity that exhibits as uninhibited bladder contraction and detrusorsphincter dyssynergia in which the sphincter activity is often uncoordinated in relation to bladder contraction. Lesions located in the suprapontine region often result in uninhibited bladder contractions resulting from lack of inhibition by the cerebral cortex. This circumstance leaves relaxation of the urethral sphincter intact, resulting in detrusor overactivity alone and a sphincter that is synergistic in relation to bladder contraction.²¹

Classification of Neurogenic Bladder

Several different classifications have been used to categorize NGB dysfunction, and each type has its own advantages and potential clinical utility. Classifications may be based on urodynamic findings, neurourologic criteria, or lower urinary tract function. One well-accepted classification system based on the location of the neurologic lesion in NGB may be used to guide pharmacologic therapies and other interventions. Using this system, NGB arises from identified neurologic locations and conditions^1,24:

• Lesions above the brain stem: The loss of the normal inhibition of a reflexic bladder contraction results in detrusor overactivity. Common symptoms include urinary frequency, urgency, and urge urinary incontinence. Bladder sensation can be normal to decreased. The urinary sphincters should be synergistic with the bladder (ie, relax when the bladder contracts); thus, high bladder pressures should not develop. Detrusor areflexia can occur in some patients, either initially and temporarily or manifesting as permanent dysfunction.
• Complete suprasacral spinal cord lesions: These patients exhibit detrusor overactivity that may lead to urinary incontinence. In addition, detrusor-external sphincter dyssynergia can be found leading to obstructive voiding and incomplete bladder emptying. Sensation to bladder filling can be normal to decreased. In addition, if the lesion is located above T6, the patient may experience autonomic hyperreflexia.
• Trauma or disease to the sacral spinal cord: These patients exhibit detrusor arreflexia and do not usually have involuntary bladder contractions. Depending on the type and extent of neurologic injury, decreased bladder compliance may occur during filling. An open smooth sphincter area may result but the striated sphincter may exhibit varied types of dysfunction, although this area usually maintains a resting sphincter tone and cannot be controlled voluntarily. Sensation to bladder filling can be normal to decreased.
• Interruption of the peripheral reflex arc (injury distal to the spinal cord): NGB dysfunction in this situation may be similar to what occurs with distal spinal cord or nerve root injury. Detrusor arreflexia is usually present and may lead to low compliance. The smooth sphincter is likely incompetent, and the striated sphincter may exhibit fixed residual tone that cannot be relaxed voluntarily. Sensation to bladder filling can be normal to decreased.

Neurourologic Evaluation of Neurogenic Bladder/Urodynamics

Thorough evaluation of the patient with possible NGB is essential to assess lower urinary tract function. When obtaining a patient history, clinicians should inquire about prior genitourinary conditions or surgeries, voiding history and complaints, and any medications the patient is using, as many types of drugs can affect bladder function and voiding. A urinary diary recording voiding patterns (time of void, volume of void, leakage episodes, etc) and fluid intake, and outlining any issues surrounding the bladder and voiding, can be very helpful to patient assessment and may guide treatment pathways and overall management. The physical examination should focus on both the status of the patient’s neurologic system and pelvic anatomy. Neurologic examination should include mental status, strength, sensation, and reflexes. Mechanical abnormalities that may interfere with voiding, such as enlarged prostate or bladder prolapsed, must be assessed and ruled out. Issues surrounding cognition, coordination, hand strength, mobility, family/social support, and medical care and support that may influence bladder management need to be evaluated. In patients with SCI, knowing the level of the spinal lesion is crucial, and the other characteristics of the injury (completeness, extremity tone, rectal sensation and tone, bulbocavernosus reflex) must be assessed. Laboratory evaluations should include urinalysis, serum blood urea nitrogen (BUN), and serum creatinine.¹ Post-void residual (PVR) urine volume should be assessed. Assessment of PVR volume is needed to prevent bladder overdistention and assist in determination of catheterization frequency if indicated.^1,25 If needed, further renal assessment may also be performed, including 24-hour urine creatinine clearance and nuclear isotope studies to evaluate baseline renal function and continued function over the course of treatment.¹

Urodynamic studies comprise a foundation of neurourologic assessment in patients with NGB.¹ Urodynamics is both the most authoritative and most objective method to assess abnormalities in the lower urinary tract in the filling/storage phase and during voiding. Urodynamic evaluations to assess urinary function may include PVR volume, urinary flowmetry, bladder cystometrogram (CMG), sphincter electromyography (EMG), Valsalva leak point pressure (LPP) measurement, and urethral pressure profile.^1,21 The most common study utilized is noninvasive uroflowmetry, which gauges the rate of voiding and volume voided.²¹ The volume of urine voided per unit of time, termed urinary flow, depends on detrusor contraction force and urethral resistance. Although urine flow rates are not diagnostic for NGB, high flow rates are frequently seen with neurogenic detrusor overactivity, whereas weak flow rates may indicate low detrusor pressure and/or urinary outlet obstruction.^1,21 A bladder CMG allows for bladder filling (often with saline) to evaluate for bladder capacity, compliance, sensation, presence of detrusor overactivity, and the measurement of leak point pressures. Detrusor LPP is the detrusor pressure when leakage occurs in the absence of bladder contraction or increased abdominal pressure.^1,26 Sustained high detrusor pressures may occur in NGBs with poor compliance, and higher detrusor LPPs indicate greater risk for upper urinary tract damage.^1,27 In addition to standard urodynamic studies, stress tests can be added as attempts to recreate symptoms and assess urinary leakage characteristics. Debate surrounds the usefulness of urodynamics in all patients being assessed for NGB; however, it is recommended in patients with SCI, more advanced MS, or spina bifida with substantial risk for upper urinary tract damage.^21,22,28

In 2012, the American Urological Association, in collaboration with the Society of Urodynamics, Female Pelvic Medicine, and Urogenital Reconstruction, published a consensus guideline document surrounding standards and/or recommendations for use of urodynamics in assessing urologic status and disorders in adult patients. This document included 5 specific standards or recommendations surrounding the use of urodynamics in patients with NGB28:

• Clinicians should perform PVR assessment, either as part of a complete urodynamic assessment or separately, during initial urologic evaluation of patients with relevant neurologic conditions and as part of ongoing follow-up where appropriate. (Standard; Strength of Evidence Grade B.)
• Clinicians should perform a CMG during initial urologic evaluation of patients with relevant neurologic conditions with or without symptoms and as part of ongoing follow-up when appropriate. In patients with other neurologic diseases, physicians may consider CMG an option in the urologic evaluation in patients with lower urinary tract symptoms. (Recommendation; Strength of Evidence Grade C.)
• Clinicians should perform pressure flow analysis (PFS) during initial urologic evaluation of patients with relevant neurologic conditions with or without symptoms and as part of ongoing follow-up when appropriate, in patients with other neurologic disease and elevated PVR, or in patients with persistent symptoms. (Recommendation; Strength of Evidence Grade C.)
• When available, clinicians may perform fluoroscopy at the time of urodynamics (videourodynamics) in patients with relevant neurologic disease at risk for NGB, in patients with other neurologic disease and elevated PVR, and in patients with urinary symptoms. (Recommendation; Strength of Evidence Grade C.)
• Clinicians should perform EMG in combination with CMG with or without PFS in patients with relevant neurologic disease at risk for NGB, in patients with other neurologic disease and elevated PVR, and in patients with urinary symptoms. (Recommendation; Strength of Evidence Grade C.)

Conclusion

NGB and associated lower urinary tract dysfunction present serious problems for both the patients with neurologic disorders and for the clinicians managing these patients. NGB can create substantial burdens for patients both healthwise and socially, including demands placed on their families and various caregivers. Clinicians managing these patients are challenged to provide comprehensive diagnosis and assessment of bladder dysfunction to guide them to appropriate individualized treatment pathways. Better understanding of the relationship between neurologic disorders and NGB, thorough neurourologic evaluation, and focused use of urodynamics may assist clinicians to better manage NGB, its symptoms and complications, and, ultimately, enhance both outcomes and quality of life in patients with these disorders.

Author affiliations: Department of Urology, Keck School of Medicine, University of Southern California, Los Angeles, CA; Department of Urology, Rancho Los Amigos National Rehabilitation Center, Downey, CA.

Funding source: This activity is supported by an educational grant from Allergan, Inc.

Author disclosure: Dr Ginsberg reports receipt of honoraria and serving as a consultant/advisory board member for Allergan, Inc, American Medical Systems, and Pfizer. Dr Ginsberg also reports receipt of lecture fees for speaking at the invitation of a commercial sponsor from Allergan, Inc.

Authorship information: Concept and design; analysis and interpretation of data; drafting of the manuscript; and critical revision of the manuscript for important intellectual content.

Address correspondence to: David Ginsberg, MD, 1441 Eastlake Ave, Suite 7416, Los Angeles, CA 90033. E-mail: Ginsberg@med.usc.edu.

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