Micro-organisms
Candida in its pathogenic hyphal form is occasionally seen in biopsies of idiopathic leukoplakia. It is debated whether candida infection is a primary cause of leukoplakia with or without dysplasia, or a superimposed (secondary) infection that occurs after the development of the lesion. It is known that Candida species thrive in altered tissues. Some leukoplakias with dysplasia reduce or disappear entirely following use of antifungal medication. Smoking, which as discussed above can lead to the development of leukoplakia, can also promote oral candidiasis. Candida in association with leukoplakia should not be confused with white patches which are primarily caused by candida infection, such as chronic hyperplastic candidiasis ("candidal leukoplakia").The involvement of viruses in the formation of some oral white lesions is well established, e.g. Epstein-Barr virus in oral hairy leukoplakia (which is not a true leukoplakia). Human papilloma virus (HPV), especially HPV 16 and 18, is sometimes found in areas of leukoplakia, however, since this virus can be coincidentally found on normal, healthy mucosal surfaces in the mouth, it is unknown if this virus is involved in the development of some leukoplakias. In vitro experimentation has demonstrated that HPV 16 is capable of inducing dysplastic changes in previously normal squamous epithelium. Epithelial atrophy
Leukoplakia is more likely to develop in areas of epithelial atrophy. Conditions associated with mucosal atrophy include iron deficiency, some vitamin deficiencies, oral submucous fibrosis, syphilis and sideropenic dysphagia. Trauma
Another very common cause of white patches in the mouth is frictional or irritational trauma leading to keratosis.
The degree of hyperkeratosis, epithelial thickness (acanthosis/atrophy), dysplasia and inflammatory cell infiltration in the underlying lamina propria are variable. In mucous membranes, hyperkeratosis can be defined as "an increase in the thickness of the keratin layer of the epithelium, or the presence of such a layer in a site where none would normally be expected." In leukoplakia, the hyperkeratosis varies in thickness and may be either ortho- or para-keratosis, (depending upon whether cell nuclei are lost or retained in the superficial layers respectively), or a mixture of both in different areas of the lesion.The epithelium may show hypertrophy (e.g. acanthosis) or atrophy. Red areas within leukoplakia represent atrophic or immature epithelium which has lost the ability to keratinize. The transition between the lesion and normal surrounding mucosa may be well-demarcated, or poorly defined. Melanin, a pigment naturally produced in oral mucosa, can leak from cells and give a grey color to some leukoplakia lesions.Hyperkeratosis and altered epithelial thickness may be the only histologic features of a leukoplakia lesion, but some show dysplasia. The word "dysplasia" generally means "abnormal growth", and specifically, in the context of oral red or white lesions, refers to microscopic changes ("cellular atypia") in the mucosa that indicate a risk of malignant transformation. When dysplasia is present, there is generally an inflammatory cell infiltration in the lamina propria. The following are commonly cited as being possible features of epithelial dysplasia in leukoplakia specimens:
Cellular pleomorphism, in which cells are of abnormal and different shapes.