The patient's symptoms, medical history and findings on examination are largely enough for the treating physician to diagnose lichen planus. Yet, there may be cases in which the early lesions resemble those of psoriasis or atopic dermatitis (in skin affection); leucoplakia or candidiasis (in oral affection), etc. A punch biopsy may be required in such cases to confirm the diagnosis or to rule out another condition. The skin biopsy is examined under a microscope and the tell-tale appearance of the lesions confirms the diagnosis.
In cases of oral lichen planus, in order to distinguish it from whitish precancerous plaques called leukoplakia, a biopsy of the oral lesions can be very valuable.