What is the appropriate workup for a healthy 22-year-old with left-sided numbness?

Workup for Left-Sided Numbness in a Healthy 22-Year-Old

In a healthy 22-year-old with left-sided numbness, immediately obtain brain MRI with and without contrast to rule out stroke, demyelinating disease, or mass lesion, as unilateral sensory symptoms in a young adult warrant urgent neuroimaging regardless of apparent health status. 1

Immediate Assessment and Red Flags

Critical History Elements

• Onset and progression: Sudden onset (<24 hours) suggests stroke or transient ischemic attack, while subacute progression (days to weeks) suggests demyelinating disease, tumor, or inflammatory process 1
• Distribution pattern: Determine if numbness involves face, arm, and leg together (suggesting cortical or subcortical lesion) versus isolated limb involvement (suggesting peripheral or spinal cord pathology) 1
• Associated symptoms requiring immediate action:
  • Visual changes, diplopia, or vision loss (suggests posterior circulation stroke, demyelinating disease, or mass effect) 1, 2
  • Headache with numbness (raises concern for stroke, venous thrombosis, or mass lesion) 1
  • Weakness accompanying numbness (increases stroke probability significantly) 1
  • Ataxia, vertigo, or dizziness (suggests posterior fossa pathology) 3, 4
  • Seizure activity (suggests cortical involvement) 1

Physical Examination Priorities

• Sensory testing: Map exact distribution of numbness using pinprick and light touch to distinguish cortical (hemibody), brainstem (crossed findings), or peripheral patterns 1
• Motor examination: Test for subtle weakness that patient may not report, particularly facial asymmetry, arm drift, and leg strength 1
• Cranial nerve screening: Specifically assess for pupillary asymmetry, extraocular movements, facial sensation, and other cranial neuropathies 1, 2
• Cerebellar testing: Finger-to-nose, heel-to-shin, and gait assessment to detect posterior fossa lesions 1, 3
• NIH Stroke Scale: Document baseline severity even in young patients, as this standardizes assessment 1

Diagnostic Imaging Algorithm

First-Line Imaging

• Brain MRI with and without gadolinium contrast is mandatory as the initial imaging study, as it detects acute stroke (diffusion-weighted imaging), demyelinating plaques, tumors, vascular malformations, and venous thrombosis that CT misses 1
• MR venography (MRV) should be added if headache accompanies numbness, as isolated cortical vein thrombosis presents with focal deficits and is easily missed on routine MRI 1
• CT brain is insufficient as the sole imaging modality in a young patient with isolated numbness, though it may be obtained emergently if MRI is unavailable and stroke is suspected 1

Additional Vascular Imaging

• MR angiography (MRA) of head and neck should be obtained if MRI shows acute infarction or if clinical suspicion for arterial dissection exists (particularly with neck pain or trauma history) 1
• CT angiography (CTA) is an acceptable alternative if MRA is contraindicated 1

Laboratory Evaluation

Essential Initial Labs

• Complete blood count with differential: Evaluate for thrombocytosis, polycythemia, or leukemia that can cause vascular events 3
• Comprehensive metabolic panel: Rule out metabolic causes and assess renal function before contrast imaging 1
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP): Screen for vasculitis, though giant cell arteritis is exceedingly rare under age 50 5
• Hemoglobin A1c and fasting glucose: Diabetes is uncommon at age 22 but can cause vascular events 2

Hypercoagulability Workup (if stroke confirmed)

• Antiphospholipid antibodies, protein C, protein S, antithrombin III, factor V Leiden, prothrombin gene mutation should be sent if imaging confirms stroke in a young patient without obvious risk factors 1
• Homocysteine level as elevated levels increase stroke risk in young adults 1

Additional Testing Based on Clinical Context

• Lumbar puncture with CSF analysis (glucose, protein, cell count, oligoclonal bands, cytology) if MRI suggests demyelinating disease, infection, or leptomeningeal process 1, 4
• Infectious serologies (Lyme, syphilis, HIV) if inflammatory or infectious etiology suspected 1

Differential Diagnosis Priorities in Young Adults

Most Likely Etiologies

• Demyelinating disease (multiple sclerosis): Most common cause of focal neurologic deficits in young adults, presents with subacute sensory symptoms, often with MRI showing periventricular white matter lesions 1
• Migraine with aura: Can cause transient unilateral numbness lasting minutes to hours, but diagnosis of exclusion requiring normal imaging 1
• Functional neurological disorder: Increasingly recognized cause of sensory symptoms in young adults, but requires positive functional signs on examination and normal imaging 1
• Arterial dissection: Particularly carotid or vertebral artery dissection from minor trauma, presents with acute numbness and may have associated neck pain 1

Cannot-Miss Diagnoses

• Stroke from paradoxical embolism: Patent foramen ovale with venous thromboembolism causing arterial stroke in young patients 1
• Cerebral venous thrombosis: Particularly in women on oral contraceptives, presents with headache and focal deficits 1
• Brain tumor or vascular malformation: Can present with isolated sensory symptoms before other manifestations 1, 3
• Numb chin syndrome: If numbness isolated to chin/lower lip, strongly associated with malignancy (breast cancer, lymphoma) even in young patients and requires immediate oncologic workup 6, 7

Critical Pitfalls to Avoid

• Never attribute unilateral numbness to anxiety or stress without neuroimaging, as functional disorders are diagnoses of exclusion requiring normal imaging and positive functional signs 1
• Do not delay MRI for days or weeks while pursuing outpatient workup, as acute stroke in young adults requires urgent evaluation even if symptoms are mild 1
• Do not assume "healthy" status excludes serious pathology, as young adults can have undiagnosed hypercoagulable states, cardiac abnormalities, or malignancies 1, 7
• Do not miss bilateral symptoms or progression, as these significantly increase likelihood of serious pathology requiring urgent intervention 1, 2

Timeframe for Evaluation

• Same-day emergency department evaluation if symptoms are acute (<24 hours), progressive, or associated with headache, weakness, or visual changes 1
• Urgent outpatient MRI within 24-48 hours if symptoms are stable, isolated sensory changes without red flags, but patient should be instructed to return immediately if symptoms worsen 1
• Neurology consultation within 1 week after imaging is obtained to interpret results and guide further workup 1