What factor deficiencies are associated with a sore red tongue, specifically vitamin B12 (cobalamin) deficiency, iron deficiency, or vitamin C deficiency?

Sore Red Tongue and Nutritional Deficiencies

All three deficiencies—vitamin B12, iron, and vitamin C—can cause a sore red tongue (glossitis), but vitamin B12 deficiency is the most commonly associated and clinically significant cause, particularly because oral manifestations often appear before hematological changes and can signal impending irreversible neurological damage. 1

Vitamin B12 Deficiency and Glossitis

Glossitis is a recognized symptom of vitamin B12 deficiency and may appear before anemia develops. 1 The oral manifestations are particularly important because:

• Oral signs can precede systemic markers of deficiency by months or years, making early recognition crucial to prevent irreversible neurological damage 2, 3
• Patients present with glossitis, glossodynia (painful tongue), papillary atrophy, erythematous areas, burning sensations, dysgeusia, and lingual paresthesia 4, 3
• The tongue may appear swollen with surface ulceration and atrophic changes 5
• Neurological damage from B12 deficiency is reversible only when replacement therapy is initiated early, before permanent spinal cord degeneration occurs 2, 6

Clinical Significance

The British Medical Journal guidelines emphasize that up to 50% of patients with "normal" serum B12 levels have metabolic deficiency when measured by methylmalonic acid, meaning standard testing can miss functional deficiency 1 This is particularly problematic because:

• Neurological symptoms often appear before hematological changes in one-third of cases 1, 6
• Subacute combined degeneration of the spinal cord can progress despite normal serum B12 levels 1
• Macrocytosis without anemia may be the only laboratory finding when oral symptoms first appear 2

Iron Deficiency and Glossitis

Iron deficiency also causes glossitis and should be included in the differential diagnosis. 5 The mechanism involves:

• Impaired cellular turnover in rapidly dividing oral epithelial cells 5
• Similar presentation with papillary atrophy and tongue inflammation 5
• Often coexists with other nutritional deficiencies, complicating the clinical picture 5

Vitamin C Deficiency and Oral Manifestations

Vitamin C deficiency (scurvy) causes oral manifestations, though glossitis is less prominent than gingival changes. 5 The primary oral features include:

• Gingival inflammation and bleeding more prominent than tongue changes 5
• Surface ulceration can occur but is not the primary presentation 5

Diagnostic Approach

When a patient presents with a sore red tongue, perform hematologic screening including complete blood count, serum iron, vitamin B12, and folate levels. 5 The algorithm should be:

1. Order initial testing: CBC with MCV, serum B12, iron studies, and folate 5
2. If B12 <180 pg/mL (<150 pmol/L): diagnose deficiency and treat immediately 7
3. If B12 180-350 pg/mL (indeterminate range): measure methylmalonic acid (MMA) 7
4. If MMA >271 nmol/L: confirms functional B12 deficiency despite "normal" serum levels 7
5. Check for macrocytosis on CBC, which may be present even without anemia 1, 2

Critical Pitfall to Avoid

Never administer folic acid before treating B12 deficiency, as it may mask anemia while allowing irreversible neurological damage to progress. 1, 8 This is particularly dangerous because:

• Folic acid can correct the megaloblastic anemia 1
• Neurological deterioration continues unchecked, leading to permanent spinal cord damage 1
• Subacute combined degeneration becomes irreversible if treatment is delayed 1

Treatment Priorities

For confirmed B12 deficiency with oral manifestations, initiate hydroxocobalamin 1 mg intramuscularly immediately. 1 The specific protocol depends on neurological involvement:

• Without neurological symptoms: hydroxocobalamin 1 mg IM three times weekly for 2 weeks, then 1 mg IM every 2-3 months for life 1
• With neurological symptoms: hydroxocobalamin 1 mg IM on alternate days until no further improvement, then 1 mg IM every 2 months 1
• Oral symptoms typically regress within one month of replacement therapy 2, 4

The key clinical message is that glossitis and oral manifestations should prompt immediate investigation for vitamin B12 deficiency, as these signs can appear before irreversible neurological damage occurs and represent a critical window for intervention. 2, 3