What are the possible causes of left-sided numbness in a patient?

Left-Sided Numbness: Differential Diagnosis and Evaluation

Left-sided numbness most commonly indicates a right hemisphere stroke (particularly right middle cerebral artery territory), but the specific pattern of involvement—whether face, arm, leg, or combinations thereof—is critical for localization and must be urgently evaluated with neuroimaging to rule out acute ischemic stroke. 1, 2

Critical Initial Distinction: Stroke vs. Other Etiologies

Acute Stroke Presentations

If left-sided numbness involves the face AND body (arm/leg) on the same side, this localizes to the contralateral (right) cerebral hemisphere, specifically the right middle cerebral artery (MCA) or right internal carotid artery (ICA) territory. 1, 2

• Face and arm involvement without leg weakness is classic for MCA territory stroke 1
• Right-sided sensory loss or paresthesias affecting the left side of the body indicates right hemisphere ischemia 2
• Every minute counts in acute stroke—immediate transfer to an emergency department with CT/MRI capability and tPA access is mandatory 1

Key distinguishing feature: Cortical lesions produce contralateral deficits only (left-sided symptoms = right hemisphere lesion). 3

Brainstem Stroke Pattern (Critical Pitfall)

If left-sided facial numbness occurs WITH right-sided body numbness (crossed pattern), this indicates brainstem localization, not cortical stroke. 3

• Ipsilateral facial involvement with contralateral body symptoms distinguishes brainstem infarction from hemispheric stroke 3
• Urgent MRI with diffusion-weighted imaging (DWI) is essential, as pontine infarcts can be as small as 4mm and easily missed on CT 3
• Associated symptoms may include vertigo, ataxia, diplopia, or dysmetria 4

Immediate Diagnostic Approach for Suspected Stroke

Imaging Protocol

Non-contrast CT head is the minimum required imaging to exclude intracranial hemorrhage before thrombolysis, but MRI with DWI is preferred if immediately available. 1, 2

• CT angiography from aortic arch to vertex must be completed within 24 hours to identify large vessel occlusion requiring endovascular thrombectomy 1, 2
• Establish exact time of symptom onset to determine eligibility for IV tPA (within 4.5 hours) or thrombectomy 1, 2

Critical Management Pitfall

Do not treat hypertension aggressively in acute stroke unless BP >185/110 mmHg for tPA candidates or >220/120 mmHg otherwise, as cerebral perfusion depends on elevated blood pressure. 1

Non-Stroke Causes of Left-Sided Numbness

Peripheral Neuropathy Patterns

Distal symmetric numbness affecting both feet (not unilateral) suggests polyneuropathy, which can be seen in diabetes, amyloidosis, or toxic/metabolic causes. 5

• Diabetic peripheral neuropathy typically causes bilateral distal sensory loss, not isolated left-sided symptoms 5
• Small-fiber neuropathy may not be detected by conventional nerve conduction studies and requires skin biopsy for epidermal nerve fiber density 5
• Amyloid polyneuropathy presents with distal sensory loss, reduced reflexes, and wide-based unsteady gait 5

Carpal Tunnel Syndrome and Radiculopathy

Carpal tunnel syndrome causes numbness in the median nerve distribution (thumb, index, middle fingers) and may be confused with polyneuropathy. 5

• Lumbar stenosis causes neurogenic claudication with numbness/pain in legs after walking, relieved by sitting—opposite pattern from polyneuropathy 5
• These syndromes are distinct from true hemispheric or brainstem lesions 5

Trigeminal Neuropathy

Progressive facial numbness, especially if isolated to the left face/chin, necessitates evaluation for malignancy or autoimmune disease. 6, 7

• Numb chin syndrome can be the earliest sign of leptomeningeal carcinomatosis or metastatic disease 6
• Facial or intraoral numbness requires periodic evaluation and vigilance, even years after presentation if no diagnosis is initially made 7
• MRI brain, CSF analysis, and systemic imaging may be required 6

Carotid Artery Stenosis

Hemispheric ischemia from carotid stenosis typically presents with contralateral weakness, paralysis, or numbness affecting the same side of the body. 5

• Duplex ultrasonography (DUS) is the first-line test to detect extracranial carotid artery stenosis 5
• Symptoms are usually caused by distal embolization rather than hypoperfusion 5

Red Flags Requiring Urgent Evaluation

• Acute onset (minutes to hours): Stroke until proven otherwise 1, 2
• Progressive symptoms over days to weeks: Consider structural lesion, malignancy, or inflammatory process 8, 6
• Crossed pattern (face on one side, body on other): Brainstem localization 3
• Associated cognitive decline or behavioral changes: Consider paraneoplastic syndrome, leptomeningeal disease, or rapidly progressive neuropathy 9, 6
• Daily falls with numbness: Suggests severe polyneuropathy or central lesion requiring hospitalization 9

Common Pitfalls to Avoid

• Do not assume bilateral symptoms are required for polyneuropathy—asymmetric presentations can occur early 8
• Do not delay neuroimaging for extensive vascular workup in acute stroke—non-contrast CT is sufficient to initiate thrombolysis 1
• Do not dismiss isolated facial numbness as benign—it may represent early malignancy or autoimmune disease 6, 7
• Do not confuse carpal tunnel syndrome or radiculopathy with central nervous system pathology—pattern recognition is key 5