What causes numbness in the tongue?

Causes of Tongue Numbness

Tongue numbness results from either peripheral nerve injury (most commonly lingual nerve trauma from dental procedures), central nervous system lesions (particularly thalamic stroke), or neuropathic conditions (including burning mouth syndrome, post-traumatic trigeminal neuropathy, and diabetic neuropathy). 1

Primary Peripheral Nerve Causes

Lingual nerve injury is the most common cause of tongue numbness, typically occurring during:

• Lower third molar extractions - the most frequent iatrogenic cause 2
• Other oral surgical procedures that place the lingual nerve at risk 2
• Salivary stone (sialolithiasis) causing intermittent compression of the lingual nerve, presenting with episodic unilateral tongue numbness 3

The numbness is typically unilateral and may be accompanied by altered sensation or complete anesthesia of the affected hemitongue. 2

Central Nervous System Causes

Thalamic stroke involving the ventroposteromedial (VPM) nucleus can cause isolated numbness of the tongue tip and lower lip:

• Small hemorrhages in the medial part of the thalamus, particularly within the VPM nucleus, can present with severe numbness restricted to the tip of the tongue and ipsilateral lower lip 4
• The somatosensory impulse from the tongue travels via the lingual nerve to the contralateral medial VPM proper through the trigeminal spinal nucleus 4
• Central neurological involvement should not be overlooked when sensory disturbance is restricted to the tongue tip and lip 4

Neck-tongue syndrome presents with neck/head pain accompanied by ipsilateral tongue dysesthesia with sudden head rotation, caused by C2 nerve root compression or inferior oblique muscle hypertrophy. 5

Neuropathic Pain Conditions

Post-traumatic trigeminal neuropathic pain develops within 3-6 months following dental procedures or facial trauma:

• Presents as continuous burning, tingling sensations 1
• Associated with history of dental procedure or trauma 1
• May include allodynia or other sensory changes 1
• Managed with neuropathic pain medications 1

Burning mouth syndrome (BMS) commonly affects the tongue, particularly the tip bilaterally:

• Characterized by burning, stinging, or itchy sensations with normal-appearing oral mucosa 1, 6
• Predominantly affects peri- and post-menopausal women 1, 6
• Secondary causes include oral candidiasis, haematological disorders, autoimmune disorders, and pharmacological side-effects 1
• In diabetic patients, BMS is significantly associated with peripheral neuropathy and female gender 7

Post-herpetic neuralgia following herpes zoster can cause continuous burning, tingling, or numbness at the site of previous infection in the oral cavity. 1, 6

Systemic and Metabolic Causes

Diabetic peripheral neuropathy can manifest as tongue numbness or burning:

• Type 1 diabetes patients with BMS are significantly more likely to have diabetic peripheral neuropathy 7
• The neuropathic process underlying diabetic peripheral neuropathy may be the source of oral symptoms 7

Haematological disorders, autoimmune disorders, and nutritional deficiencies (particularly vitamin B12, iron) can cause secondary tongue numbness or burning sensations. 1, 6

Red Flags Requiring Urgent Evaluation

Malignancy must be considered when tongue numbness is accompanied by:

• New numbness in the oral cavity or cheek with intraoral swelling or ulceration 1
• Unilateral symptoms with induration or non-healing lesions 8
• Palpable neck mass or lymphadenopathy 1, 8
• History of tobacco/alcohol use in patients over 40 years 8

Giant cell arteritis should be considered in patients over 50 with facial/tongue symptoms, as tongue artery involvement can cause cyanosis of the tongue and requires high-dose steroids within 2 weeks to prevent vision loss. 1

Diagnostic Approach

For acute unilateral tongue numbness:

• Assess for recent dental procedures or oral trauma 1
• Examine for visible mucosal lesions, ulcerations, or masses 1, 6
• Palpate the floor of mouth and submandibular area for stones or masses 1, 8
• Consider thalamic stroke if accompanied by other neurological symptoms 4

For chronic bilateral burning or numbness:

• Perform laboratory testing including CBC with differential, iron studies, vitamin B12, fasting glucose/HbA1c, vitamin D, and thyroid function tests 6
• Exclude secondary causes including candidiasis, nutritional deficiencies, and medication side-effects 1, 6
• Consider tongue biopsy if suspicious lesions are present 6