What causes numbness on the right side of the tongue?

Unilateral Tongue Numbness: Diagnostic Approach

Numbness on the right side of the tongue requires urgent evaluation to exclude central nervous system pathology, particularly stroke involving the thalamus or sensory cortex, as well as hypoglossal nerve (CN XII) compression along its course from the brainstem to the tongue. 1

Immediate Diagnostic Priorities

Rule Out Central Nervous System Causes

• Thalamic stroke involving the ventroposteromedial (VPM) nucleus can present with isolated numbness of the tongue tip and lower lip on the same side, even without other neurological deficits 2
• Cortical infarction at the postcentral gyrus of the contralateral parietal lobe can cause isolated tongue numbness without other symptoms 3
• Central causes must not be overlooked when sensory disturbance is restricted to the tongue, as these can present without obvious accompanying neurological signs 2, 3

Assess for Hypoglossal Nerve (CN XII) Pathology

• Hypoglossal nerve palsy presents with dysarthria and tongue deviation toward the affected side upon protrusion, though isolated sensory symptoms are less common 1
• The hypoglossal nerve can be injured anywhere along its course: brainstem nucleus, premedullary cistern, hypoglossal canal, carotid space, or sublingual space 1
• Most common causes of isolated CN XII palsy include neoplasms involving the hypoglossal canal, malignant tumors in the carotid or sublingual space, and internal carotid artery dissection 1

Essential Clinical Assessment

Key History Elements

• Onset characteristics: Sudden onset suggests vascular etiology (stroke, dissection), while gradual onset suggests compressive lesion 1, 2
• Associated symptoms: Dysarthria, tongue weakness, headache, or other cranial nerve involvement 1, 4
• Risk factors: Hypertension, diabetes, tobacco use, alcohol consumption, prior trauma, or recent dental procedures 1, 2

Physical Examination Findings

• Observe tongue position at rest and during protrusion for deviation (indicates motor involvement) 1
• Assess for tongue atrophy or fasciculations (suggests chronic nerve injury) 1
• Palpate neck for masses and assess for lymphadenopathy 5
• Complete head and neck examination including visualization of oral mucosa for lesions 5

Imaging Algorithm

First-Line Imaging

• MRI brain with contrast is the initial study of choice to evaluate for thalamic or cortical stroke, as well as to directly image the brainstem and intracranial segments of CN XII 1, 2, 3
• MRI provides excellent soft tissue contrast to characterize nerve sheath tumors, neuritis, and carotid space pathology 1

Complementary Imaging

• CT neck with contrast provides complementary information, characterizing osseous integrity of the hypoglossal canal and surrounding skull base 1
• Thin-cut high-resolution bone windows through the posterior skull base are essential 1
• MR or CT angiography should be obtained if vascular causes (dissection, vascular compression) are suspected 4

Peripheral Nerve Considerations

Lingual Nerve Compression

• Sialolithiasis (salivary stones) can cause intermittent compression of the lingual nerve, presenting with episodic unilateral tongue numbness 6
• This is a benign, treatable cause that should be considered, particularly if symptoms are intermittent 6
• Removal of the obstruction typically relieves symptoms 6

Post-Traumatic Causes

• Recent head trauma can cause traction injury to the hypoglossal nerve at the skull base 7
• Dental procedures or facial trauma within 3-6 months can lead to post-traumatic trigeminal neuropathic pain with burning or tingling 8

Critical Pitfalls to Avoid

• Do not dismiss unilateral tongue numbness as benign without neuroimaging, as central causes (stroke) can present with isolated sensory symptoms 2, 3
• Do not delay imaging in patients with sudden onset, hypertension, or vascular risk factors 2
• Consider malignancy in patients with progressive symptoms, particularly those with tobacco/alcohol use or unilateral pain with visible lesions 5
• Assess for carotid dissection if there is associated headache, neck pain, or Horner syndrome 1

When to Refer

• Immediate neurology consultation for suspected acute stroke 2, 3
• Neurosurgery consultation if imaging reveals compressive lesion or vascular anomaly 1, 4
• Otolaryngology referral for suspected malignancy or if biopsy of oral lesions is needed 5