What are the causes of burning tongue (burning mouth syndrome)?

Causes of Burning Tongue

Primary vs Secondary Classification

Burning tongue (burning mouth syndrome) should be classified as either primary (idiopathic/neuropathic) or secondary (caused by identifiable local, systemic, or pharmacological factors), with secondary causes requiring systematic exclusion before diagnosing primary BMS. 1

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Secondary Causes (Must Be Excluded First)

Local Oral Factors

• Oral candidiasis (fungal infection) diagnosed by scraping and KOH preparation 1
• Mucosal lesions including traumatic ulceration from sharp edges of residual tooth roots/crowns, ill-fitting dentures, thermal burns, or chemical injury 1, 2
• Xerostomia (dry mouth) from various causes 3
• Denture-related lesions and hypersensitivity reactions 4

Hematological and Nutritional Deficiencies

• Anemia (iron deficiency) - check complete blood count with differential, ferritin, serum iron, and TIBC 1
• Vitamin B12 deficiency - a well-established cause requiring serum B12 testing 1
• Riboflavin (vitamin B2) deficiency manifesting with glossitis, cheilosis, and angular stomatitis 1
• Pyridoxine (vitamin B6) deficiency causing glossitis and seborrheic dermatitis with cheilosis 1
• Zinc deficiency leading to glossitis, taste alterations, and hair loss 1

Autoimmune and Endocrine Disorders

• Sjögren's syndrome and sicca syndrome presenting with oral burning 1
• Thyroid disorders, particularly hyperthyroidism causing tongue erythema and burning - check TSH and free T4 1, 2
• Diabetes mellitus - check fasting glucose and HbA1c 2, 4

Neuropathic Causes

• Post-herpetic neuralgia following herpes zoster causing continuous burning, tingling, or itchy sensations at the site of previous infection 2
• Post-traumatic trigeminal neuropathic pain developing within 3-6 months following dental procedures or facial trauma 1, 2

Pharmacological Side Effects

• Various medications can cause oral burning and must be reviewed in the medication history 5, 1, 2

Infectious Causes

• Scarlet fever and Kawasaki disease can present with oral burning symptoms 1

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Primary Burning Mouth Syndrome

Primary BMS is a disorder of peripheral nerve fibers with central nervous system changes, confirmed through neurophysiological testing, biopsies, and functional MRI. 1

Pathophysiology

• Small fiber neuropathy with significantly lower density of epithelial nerve fibers in tongue biopsies compared to controls 1, 6
• Altered sensory processing with significantly higher sensory thresholds than controls 6
• Represents a neuropathic pain condition rather than a psychological disorder 4, 6

Clinical Characteristics

• Predominantly affects peri- and post-menopausal women, typically occurring within 3-12 years after menopause 1, 2, 6
• Continuous burning, stinging, or itchy sensation most commonly affecting the tongue tip bilaterally, lips, palate, and buccal mucosa 5, 1, 2
• Normal-appearing oral mucosa on examination with no visible mucosal alterations 1, 3
• Associated symptoms include dry mouth, abnormal (metallic) taste, depression, and poor quality of life 5, 1, 6
• Pain severity ranges from mild to severe and typically increases in intensity during evening and at night 5, 7

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Diagnostic Approach

Essential Clinical Evaluation

• Document onset timing, medication use, systemic diseases, and dental procedures in the clinical history 1
• Perform thorough oral examination to identify mucosal lesions, candidiasis, or traumatic factors 1, 2
• Assess for traumatic factors including sharp edges of residual tooth roots/crowns and ill-fitting dentures 2

Required Laboratory Workup

• Complete blood count with differential to identify anemia 1, 2
• Iron studies (ferritin, serum iron, TIBC) 1, 2
• Vitamin B12 level 1, 2
• Fasting glucose and HbA1c 2
• Thyroid function tests (TSH, free T4) 2
• Vitamin D 25(OH) 2

Additional Diagnostic Procedures

• Oral swabs if fungal or bacterial infection is suspected 8
• Tongue biopsy may be necessary to rule out malignancy, especially with unilateral pain, ulceration, or non-healing lesions 2
• Qualitative sensory testing if neuropathic etiology is suspected 5, 1

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Important Clinical Pitfalls

• Do not diagnose primary BMS until all secondary causes have been excluded - this is the most critical diagnostic principle 1, 3, 4
• Multiple concurrent causes may be present in more than one-third of patients 4
• Professional delay in diagnosis and referral occurs frequently 4
• Avoid ordering IgE levels routinely as they are nonspecific and should only be checked if specific allergic or parasitic conditions are suspected 1
• Unilateral pain, ulceration, or non-healing lesions warrant tongue biopsy to rule out malignancy 2