What is the most likely diagnosis for a patient with left leg numbness, difficulty urinating, and a history of transient visual loss, presenting with decreased strength and sensation in the left lower extremity, bilateral lower extremity hyperreflexia, and urinary retention?

Multiple Sclerosis

The most likely diagnosis is multiple sclerosis (MS), given the combination of left leg numbness with weakness, bilateral lower extremity hyperreflexia, urinary retention (700 mL postvoid residual), and a prior episode of transient visual loss that resolved spontaneously—this clinical pattern demonstrates dissemination in both space (optic nerve and spinal cord) and time (separate episodes months apart). 1, 2

Clinical Reasoning for MS Diagnosis

Dissemination in Space (Multiple CNS Locations)

• The patient has involvement of at least two distinct anatomical regions of the central nervous system: the optic nerve (prior visual loss episode) and the spinal cord (current left leg symptoms with bilateral hyperreflexia and urinary retention) 3, 2
• The bilateral lower extremity hyperreflexia indicates upper motor neuron involvement, localizing the lesion to the spinal cord rather than peripheral nerves 1
• Urinary retention with 700 mL postvoid residual reflects autonomic dysfunction from spinal cord involvement, a common MS manifestation 2

Dissemination in Time (Separate Episodes)

• The prior episode of visual loss that resolved spontaneously several months ago represents a distinct clinical attack, likely optic neuritis 4, 2
• The current presentation with leg numbness, weakness, and urinary dysfunction represents a second, separate clinical event 1
• This temporal separation of attacks fulfills the dissemination in time criterion for MS diagnosis 5

Characteristic MS Features Present

• Young adult with no prior medical history fits the typical MS demographic (disease of young adults with female predominance) 2
• Optic neuritis is one of the most common presenting symptoms of MS, affecting the optic nerve and causing transient visual loss that typically resolves 2, 5
• Spinal cord involvement causing sensory symptoms, motor weakness, and bladder dysfunction is a classic MS presentation 1, 2
• The relapsing-remitting pattern (attack with resolution, followed by new attack) is the most common MS presentation at onset 2

Why Other Diagnoses Are Less Likely

Anterior Cerebral Artery Stroke - Excluded

• Stroke would not explain the prior episode of visual loss months ago 1
• Stroke presents acutely (minutes to hours), not over 2 days 1
• Bilateral hyperreflexia with unilateral leg weakness is atypical for anterior cerebral artery territory 1
• No vascular risk factors mentioned in this young patient with no medical history 2

Cauda Equina Syndrome - Excluded

• Cauda equina affects peripheral nerves (lower motor neurons), causing hyporeflexia or areflexia, not the bilateral hyperreflexia seen here 6
• Would not explain the prior episode of visual loss 6
• Typically presents with severe back pain, which this patient explicitly denies 6
• The pattern of hyperreflexia indicates upper motor neuron (spinal cord) rather than lower motor neuron (cauda equina) pathology 7

Functional Neurological Disorder - Excluded

• Would not produce objective findings like bilateral hyperreflexia and measurable urinary retention (700 mL postvoid residual) 1
• The prior episode of visual loss with spontaneous resolution followed by a separate neurological event is highly specific for organic demyelinating disease 4, 2
• Functional disorders do not cause consistent, reproducible upper motor neuron signs 1

Recommended Next Steps

Immediate Diagnostic Workup

• MRI of brain and spinal cord with and without contrast is essential to demonstrate dissemination in space by identifying typical demyelinating lesions in multiple CNS locations (periventricular, juxtacortical/cortical, infratentorial, spinal cord, and optic nerve regions) 3, 5
• Fat-saturated sequences should be included for detection of optic nerve lesions corresponding to the prior visual loss episode 3
• Lumbar puncture for cerebrospinal fluid analysis to detect oligoclonal bands and elevated IgG index, which support inflammatory demyelinating disease 1, 2

Application of 2024 McDonald Criteria

• The diagnosis can be confirmed when MRI demonstrates typical lesions in at least four of five anatomical locations (periventricular, juxtacortical/cortical, infratentorial, spinal cord, optic nerve) without requiring additional evidence of dissemination in time, given the clinical history of two separate attacks 3
• If MRI shows lesions in fewer than four locations, additional evidence of dissemination in time through new lesions on follow-up imaging or new clinical attacks would be needed 3, 5

Critical Management Considerations

• Early diagnosis and treatment with disease-modifying immunomodulatory agents is crucial because axonal loss occurs early in MS, and patients who begin treatment earlier have significantly better outcomes than those who start later 4
• The combination of a clinically isolated syndrome (the prior visual loss) with MRI lesions is highly predictive of developing definite MS, making early intervention particularly important 4
• Urgent neurology referral is warranted for definitive diagnosis and initiation of disease-modifying therapy 4, 2

Common Pitfalls to Avoid

• Do not delay MRI imaging waiting for additional clinical attacks—early imaging can establish the diagnosis and enable prompt treatment 4, 3
• Do not attribute urinary retention solely to a peripheral cause without considering spinal cord pathology, especially with hyperreflexia present 1
• Do not dismiss the prior visual loss episode as unrelated—this represents a critical piece of evidence for dissemination in time 2, 5
• Ensure the differential diagnosis excludes other inflammatory CNS disorders (neuromyelitis optica, systemic lupus erythematosus with neuropsychiatric manifestations) through appropriate serological testing if MRI findings are atypical 7, 1