What are the potential causes of lower limb weakness with bladder involvement?

Lower Limb Weakness with Bladder Involvement: Differential Diagnosis

The combination of lower limb weakness and bladder dysfunction most commonly indicates spinal cord pathology, with tethered cord syndrome, myelomeningocele, spinal cord injury, and cauda equina lesions being the primary structural causes that require urgent neuroimaging to prevent irreversible neurological damage. 1

Spinal Cord and Cauda Equina Pathology (Primary Consideration)

Tethered Cord Syndrome

• Progressive lower limb weakness with bladder/bowel dysfunction is the hallmark presentation, often accompanied by sensorimotor disturbances that worsen with growth or sudden spinal stretching 1
• Muscle weakness typically manifests as gait disturbances, difficulty running, and inability to keep up with peers during athletic activities; muscle atrophy may develop with thinning of calf muscles ("saber shins") 1
• Bladder dysfunction presents as urinary urgency, incontinence, urinary tract infections, dribbling stream, incomplete emptying, or inability to void 1
• Sensory abnormalities generally start distally in the leg and progress proximally over time; a "suspended" sensory loss pattern may occur with preserved sensation above and below the abnormal area 1
• In those with bowel and bladder dysfunction combined with lower limb upper motor neuron signs, lumbar spine MRI should be obtained to rule out tethered cord, especially when a sacral dimple is present 1

Myelomeningocele (MMC)

• MMC represents the most common and serious dysraphic malformation compatible with life, resulting from localized failure of primary neurulation 1
• Patients require PVR assessment during initial urological evaluation and as part of ongoing follow-up, with complex cystometrography (CMG) recommended at initial consultation even in the absence of symptoms 1
• The birth prevalence in the United States is approximately 0.2 per 1000 live births, with variation by ethnicity (highest among Hispanic infants at 1.12 per 1000) 1

Spinal Cord Injury

• Complex CMG should be performed during initial urological evaluation of patients with spinal cord injury (after the spinal shock phase) with or without symptoms 1
• Autonomic dysreflexia is a life-threatening complication that requires continuous hemodynamic monitoring during urodynamic testing and cystoscopic procedures 1
• If autonomic dysreflexia develops during testing, the study must be terminated immediately, the bladder drained, and hemodynamic monitoring continued 1

Neurological Conditions with Secondary Bladder Involvement

Multiple Sclerosis

• The severity of urinary symptoms correlates directly with the degree of pyramidal impairment in the lower limbs, both reflecting the extent of spinal involvement 2
• Detrusor hyperreflexia is the commonest cystometric finding; detrusor hyperreflexia can be anticipated in patients with MS who have irritative urinary symptoms and pyramidal signs in their lower limbs 2
• More than half of patients have significantly raised post-micturition residual volume, but symptoms are largely unreliable in predicting poor bladder emptying 2

Acute Disseminated Encephalomyelitis (ADEM)

• Lower urinary tract dysfunction occurs in 33% of ADEM patients, with voiding dysfunction more common than storage symptoms 3
• LUTD is associated with occurrence of paraparesis or tetraparesis, though it does not predict functional outcome at discharge 3
• Cystometry demonstrates detrusor overactivity or underactivity; at 3-month follow-up, symptoms may persist even after recovery of other neurological deficits 3

Peripheral Neuropathies

• Diabetic neuropathy is the most common cause of peripheral neuropathy-associated bladder dysfunction, presenting as diabetic cystopathy with a hypotonic, insensitive large capacity bladder 4, 5
• Guillain-Barré syndrome, HIV-associated neuropathy, CIDP, and amyloid neuropathy are other major causes requiring consideration 4
• Objective evidence of neuropathic bladder dysfunction occurs in 71.7% of diabetic patients, with the commonest abnormality being a hypotonic, insensitive large capacity bladder that is usually asymptomatic 5

Traumatic Causes

Pelvic Fracture-Related Injuries

• Urethral injuries occur in 1.5-5% of anterior pelvic fractures and are the most common structural cause of post-traumatic urinary retention; blood at the urethral meatus is pathognomonic for urethral injury and contraindicates blind catheterization 6
• Bladder injuries occur in 6-8% of patients with pelvic fractures and can cause retention through disruption of normal bladder mechanics 6, 7
• The risk of urethral injury increases by 10% for every 1-mm increase in pubic symphysis diastasis 6

Critical Diagnostic Algorithm

Immediate Evaluation

• Perform focused neurological examination assessing lower limb motor strength, deep tendon reflexes, sensory distribution (particularly L5-S1), and rectal tone 1
• Obtain post-void residual (PVR) assessment immediately to distinguish between storage and emptying dysfunction 1
• Check for cutaneous markers overlying the spine (sacral dimples, hairy patches, lipomas, hemangiomas) that suggest underlying spinal dysraphism 1

Imaging Strategy

• Lumbar spine MRI is mandatory when lower limb upper motor neuron signs are present with bowel/bladder dysfunction to evaluate for tethered cord, spinal cord compression, or other structural lesions 1
• Brain MRI should be obtained if focal neurologic findings, muscle weakness, or abnormal deep tendon reflexes suggest central demyelinating disease 1
• In trauma patients with pelvic fracture and hematuria, contrast-enhanced CT scan with delayed urographic phase is the gold standard for evaluating bladder injuries 6

Urodynamic Testing

• Complex multichannel CMG should be performed in patients with relevant neurological conditions (spinal cord injury, myelomeningocele) during initial evaluation, even without symptoms 1
• For moderate-risk neurogenic lower urinary tract dysfunction patients, annual renal function assessment and upper tract imaging every 1-2 years is recommended 1
• Clinicians performing CMG in patients at risk for autonomic dysreflexia must be adept in its detection and prompt management, including having necessary monitoring equipment 1

Common Pitfalls to Avoid

• Do not assume bladder symptoms are simply "overactive bladder" without imaging follow-up, as unrecognized structural lesions will not respond to anticholinergics and require surgical intervention 7
• Never attempt repeated catheterization if urethral injury is suspected in trauma patients, as this increases injury severity 7
• Do not rely on symptoms alone to predict elevated post-void residual volume; objective measurement is essential as symptoms are unreliable predictors 2
• Recognize that patients may have subtle abnormalities dating back to early childhood (slow athletically, chronic constipation, late toilet training, orthopedic deformities) that suggest chronic tethered cord 1