Differential Diagnosis for Rash Inside Mouth

• Single Most Likely Diagnosis
  • Aphthous ulcers (canker sores): These are the most common cause of a rash or ulcers inside the mouth, characterized by small, painful, and recurrent lesions.
• Other Likely Diagnoses
  • Oral lichen planus: An autoimmune condition that can cause white, lacy patches or red, inflamed tissues inside the mouth.
  • Oral thrush (candidiasis): A fungal infection that can cause white patches or redness inside the mouth, often associated with immunosuppression or antibiotic use.
  • Allergic contact stomatitis: An allergic reaction to substances like food, toothpaste, or mouthwash, which can cause redness, swelling, and ulcers.
• Do Not Miss Diagnoses
  • Oral cancer: Although less common, it's crucial to consider oral cancer, especially in patients with a history of tobacco or alcohol use, as it can present with non-healing ulcers or masses.
  • Primary herpetic gingivostomatitis: A viral infection caused by herpes simplex virus, which can lead to severe mouth pain, fever, and difficulty eating or drinking.
  • Stevens-Johnson syndrome: A rare but life-threatening condition characterized by severe skin and mucous membrane lesions, often triggered by medications or infections.
• Rare Diagnoses
  • Pemphigus vulgaris: A rare autoimmune disease that causes blistering of the skin and mucous membranes, including the mouth.
  • Erythema multiforme: A rare skin condition that can affect the mouth, characterized by target-shaped lesions and often associated with infections or medications.
  • Behçet's disease: A rare condition that causes inflammation of blood vessels, which can lead to oral ulcers, genital ulcers, and eye inflammation.