It has been shown that there is high degree of inter-observer variation and poor reproducibility in how dysplasia is graded. Severe dysplasia is synonymous with the term carcinoma in situ, denoting the presence of neoplastic cells which have not yet penetrated the basement membrane and invaded other tissues. Differential diagnosis
There are many known conditions that present with a white lesion of the oral mucosa, but the majority of oral white patches have no known cause. These are termed leukoplakia once other likely possibilities have been ruled out. There are also few recognized subtypes of leukoplakia, described according to the clinical appearance of the lesion. Almost all oral white patches are usually the result of keratosis. For this reason, oral white patches are sometimes generally described as keratoses, although a minority of oral white lesions are not related to hyperkeratosis, e.g. epithelial necrosis and ulceration caused by a chemical burn (see: Oral ulceration#Chemical injury). In keratosis, the thickened keratin layer absorbs water from saliva in the mouth and appears white in comparison with normal mucosa. Normal oral mucosa is a red-pink color due to the underlying vasculature in the lamina propria showing through the thin layer of epithelium. Melanin produced in the oral mucosa also influences the color, with a darker appearance being created by higher levels of melanin in the tissues (associated with racial/physiologic pigmentation, or with disorders causing melanin overproduction such as Addisons disease). Other endogenous pigments can be overproduced to influence the color, e.g.
History
The term leukoplakia was coined in 1861 by Karl Freiherr von Rokitansky, who used it to refer to white lesions of the urinary tract. In 1877, Schwimmer first used the term for an oral white lesion. It is now thought that this white lesion on the tongue represented syphilitic glossitis, a condition not included in the modern definitions of oral leukoplakia. Since then, the word leukoplakia has been incorporated into the names for several other oral lesions (e.g. candidal leukoplakia, now more usually termed hyperplastic candidiasis). In 1930, it was shown experimentally that leukoplakia could be induced in rabbits that were subjected to tobacco smoke for 3 minutes per day. According to one source from 1961, leukoplakia can occur on multiple different mucous membranes of the body, including in the urinary tract, rectum, vagina, uterus, vulva, paranasal sinuses, gallbladder, esophagus, eardrums, and pharynx. Generally, oral leukoplakia is the only context where the term is in common usage in modern medicine. In 1988, a case report used the term acquired dyskeratotic leukoplakia to refer to an acquired condition in a female where dyskeratotic cells were present in the epithelia of the mouth and genitalia. : 480 : 806

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