Differential Diagnosis for Erythemic Lesions on the Roof of the Mouth and Buccal Mucosa

Single Most Likely Diagnosis

• Erythematous Oral Candidiasis: Given the patient's history of diabetes, which can predispose to candidal infections due to potential immune system compromise and higher glucose levels in the saliva, this diagnosis is highly plausible. The description of erythemic, painful, and itchy lesions on the roof of the mouth and buccal mucosa bilaterally aligns with the clinical presentation of erythematous oral candidiasis.

Other Likely Diagnoses

• Lichen Planus: This chronic inflammatory condition can present with erythematous and ulcerative lesions in the oral cavity, including the buccal mucosa and the roof of the mouth. It often causes discomfort and can be itchy.
• Oral Lichenoid Lesions: Similar to lichen planus, these can appear as erythematous and sometimes ulcerative lesions, often in response to allergens or irritants.
• Aphthous Ulcers: Although typically more localized and not always bilateral, aphthous ulcers can cause significant pain and may appear erythematous around the edges.

Do Not Miss Diagnoses

• Squamous Cell Carcinoma: Although less likely given the bilateral and symmetric nature of the lesions, oral cancer can present with erythematous or ulcerative lesions and must be considered, especially in patients with risk factors such as smoking or alcohol use.
• Infectious Mononucleosis (Glandular Fever): Caused by Epstein-Barr virus, this condition can lead to oral lesions and should be considered, especially if there are systemic symptoms like fever and lymphadenopathy.
• Autoimmune Disorders (e.g., Pemphigus, Pemphigoid): These conditions can cause blistering lesions that may appear erythematous and are painful, requiring prompt diagnosis and treatment to prevent serious complications.

Rare Diagnoses

• Histoplasmosis: A fungal infection that can cause oral lesions, particularly in immunocompromised patients.
• Kaposi's Sarcoma: A type of cancer that can cause oral lesions, more common in immunocompromised patients, such as those with HIV/AIDS.
• Erythema Multiforme: An immune-mediated condition that can cause oral and skin lesions, often in response to infections or medications.

Each of these diagnoses should be considered based on the patient's full clinical presentation, history, and additional diagnostic tests as necessary.