Oral Pathology and Oral Medicine
What the exam tests
Recognition of mucosal disease, correct use of the biopsy, and separation of harmless lesions from potentially malignant disorders and immune-mediated disease.
Core rules
- Leukoplakia is a clinical, exclusion diagnosis: a white patch that cannot be characterised as any other disease. It becomes a histological diagnosis only after biopsy, which is mandatory.
- Erythroplakia and speckled lesions carry a much higher risk of dysplasia or carcinoma than homogeneous leukoplakia; any ulcer persisting beyond two weeks with induration, fixation or bleeding needs biopsy.
- Recurrent aphthous stomatitis is painful, recurrent, non-keratinised-mucosa-only and heals in 7-14 days without scarring (major aphthae scar). Primary herpes occurs once, in children, with fever and generalised gingivostomatitis.
- Pemphigus vulgaris shows suprabasal acantholysis with intercellular IgG and a positive Nikolsky sign; mucous membrane pemphigoid is subepithelial with linear IgG/C3 at the basement membrane and causes scarring.
- Oral lichen planus shows Wickham striae and a band-like T-lymphocyte infiltrate; erosive forms need biopsy to exclude dysplasia.
- Pseudomembranous candidiasis wipes off leaving erythema; erythematous and hyperplastic forms do not. Predisposing factors: inhaled steroids, xerostomia, diabetes, dentures.
Worked example
A 62-year-old smoker has a 2 cm indurated, fixed ulcer on the floor of the mouth for five weeks. Reasoning: duration, induration, fixation and site (floor of mouth, lateral tongue) all point to squamous cell carcinoma, not aphthous ulceration. Incisional biopsy at the margin, imaging and urgent referral follow; a trial of steroids would delay diagnosis.
Traps that cost marks
- Calling a white patch leukoplakia before excluding frictional keratosis, candidiasis and lichen planus.
- Treating a chronic ulcer with antibiotics or antifungals instead of biopsying it.