Oral Mucosa Lesions: Differential Diagnosis

How to distinguish lichen planus, leukoplakia and other white lesions of the oral cavity, and why the WHO classification of potentially malignant disorders changes the clinical approach.

White lesions of the oral mucosa are among the most common diagnostic challenges in everyday practice, because very different conditions — from simple frictional keratosis to disorders with genuine malignant transformation potential — can present with a similar clinical appearance. The correct diagnostic path always starts by ruling out known causes: mechanical frictional keratosis, smoker's keratosis, leukoedema, white sponge nevus, candidiasis. Only after ruling out these entities, by removing any identifiable causal factor or through histological examination, can a diagnosis of leukoplakia or lichen planus be made.

Oral lichen planus presents in several clinical forms, of which the reticular form is the most common: an interlacing pattern of whitish keratotic striae, called Wickham's striae, typically bilateral and located on the buccal mucosa. Other forms include the plaque form — which can resemble leukoplakia but is distinguished by multifocal distribution — and the atrophic-erosive, symptomatic forms, which present with erythematous, ulcerated areas surrounded by reticular striae and can be mistaken for other vesiculo-erosive conditions such as mucous membrane pemphigoid or pemphigus vulgaris.

Leukoplakia, by definition, is a white thickening of the mucosa not attributable to any known identifiable cause — a diagnosis of exclusion, not a positive diagnosis based on specific features. Macroscopically it's distinguished into homogeneous forms, more common, smooth and uniform, generally asymptomatic, and non-homogeneous forms (verrucous, nodular, erythroleukoplakic), which carry a significantly higher malignant transformation risk and therefore require closer follow-up or referral to a specialist.

In 2005 the World Health Organization grouped these conditions into a category called "potentially malignant disorders", recognizing that oral cavity carcinoma is often, though not always, preceded by mucosal changes that can precede actual neoplastic transformation by years. For oral lichen planus, the most recent meta-analyses report an average malignant transformation rate between 0.5% and 2%, with an estimated annual rate between 0.3% and 0.6% — a non-negligible risk that justifies periodic follow-up even in asymptomatic forms, especially in the presence of aggravating factors like smoking, alcohol, and HPV or HCV infection.

On Oralzon you'll find diagnostic instrumentation for examining the oral mucosa and materials for biopsy sampling, essential for accurate differential diagnosis of oral mucosal lesions.