What is the differential diagnosis for a tongue ulcer?

Aphthous Ulcer: This is the most common cause of tongue ulcers, characterized by recurrent, painful, and self-limiting lesions. The high prevalence and typical presentation make it the single most likely diagnosis.

Traumatic Ulcer: Often caused by accidental biting of the tongue or other mechanical injuries, these ulcers are common and can be painful.
Oral Candidiasis: Fungal infection that can cause ulcers on the tongue, especially in immunocompromised individuals or those with poor oral hygiene.
Herpes Simplex Virus (HSV) Infection: Can cause painful ulcers on the tongue, particularly in individuals with a history of HSV infections.
Nutritional Deficiencies: Deficiencies in vitamins like B12, iron, or folate can lead to oral changes, including ulcers on the tongue.

Squamous Cell Carcinoma: Although rare, this is a potentially deadly diagnosis if missed. Ulcers that are persistent, large, or have irregular borders should raise suspicion for oral cancer.
Tuberculosis: Oral tuberculosis can present with ulcers on the tongue, and given its potential severity and the importance of early treatment, it should not be missed.
Syphilis: The secondary stage of syphilis can cause oral ulcers, including on the tongue. Given the potential for severe complications if untreated, syphilis should be considered.

Behçet's Disease: A rare condition characterized by recurrent ulcers in the mouth, including on the tongue, along with genital ulcers and eye inflammation.
Pemphigus Vulgaris: An autoimmune disease that can cause blistering of the skin and mucous membranes, including the tongue, leading to ulcers.
Erythema Multiforme: A skin condition that can also affect the mucous membranes, causing ulcers, including on the tongue, often in response to infections or medications.
Lichen Planus: An inflammatory condition that can affect the skin and mucous membranes, leading to ulcers on the tongue in some cases.