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Leukoplakia (also termed leucoplakia, leukokeratosis,〔 leukoplasia,〔 idiopathic leukoplakia,〔 idiopathic keratosis,〔 or idiopathic white patch),〔 normally refers to a condition where areas of keratosis appear as firmly attached white patches on the mucous membranes of the oral cavity, although the term is sometimes used for white patches of other gastrointestinal tract mucosal sites, or mucosal surfaces of the urinary tract and genitals.〔Underwood. General and Systemic Pathology. 4th Edition. Edinburgh, London: Churchill Livingstone 2004〕 Leukoplakia in the mouth (oral leukoplakia), is defined as "a predominantly white lesion of the oral mucosa that cannot be characterized as any other definable lesion". However, this definition is inconsistently applied, and some refer to any oral white patch as "leukoplakia".〔 Leukoplakia is a descriptive clinical term that is only correctly used once all other possible causes have been ruled out (a diagnosis of exclusion). As such, leukoplakia is not a specific disease entity, and the clinical and histologic appearance are variable, i.e. the term has no specific histologic implications.〔 Leukoplakia may be confused with other common causes of white patches in the mouth, such as oral candidiasis or lichen planus. The lesions of leukoplakia cannot be rubbed off, as would be the case in pseudomembraneous candidiasis (oral thrush). Oral leukoplakia more commonly occurs in those who smoke,〔 but often the cause is unknown (hence the name idiopathic leukoplakia).〔 Chewing tobacco is also associated with this type of lesion. Leukoplakia is a premalignant lesion, i.e. "a morphologically altered tissue in which cancer is more likely to occur than in its apparently normal counterpart".〔 The chance of transformation into oral squamous cell carcinoma (OSCC, a type of oral cancer) varies from almost 0% to about 20%, and this may occur over 1 – 30 years.〔 The vast majority of oral leukoplakias will not turn malignant,〔 however some subtypes hold greater risk than others. No interventions have been proven to reduce the risk of cancer developing in an area of leukoplakia,〔 but people are generally advised to stop smoking and limit alcohol consumption to reduce their risk.〔 Sometimes the white patch will shrink and eventually disappear after stopping smoking,〔 but this may take up to a year.〔 In many cases, areas of leukoplakia will slowly expand, become more white and thicken if smoking is not stopped.〔 Management usually involves regular review of the lesion to detect any possible malignant change early, and thereby significantly improve the prognosis, which normally is relatively poor for OSCC.〔 ==Definition== The word leukoplakia means "white patch",〔 and is derived from the Greek words λευκός - "white" and πλάξ - "plate".〔Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press.〕 Leukoplakia is a diagnosis of exclusion, meaning that which lesions are included depends upon what diagnoses are currently considered acceptable.〔 Accepted definitions of leukoplakia have changed over time and are still controversial.〔 It is possible that the definition will be further revised as new knowledge becomes available.〔 In 1984 an international symposium agreed upon the following definition: "a whitish patch or plaque, which cannot be characterized clinically or pathologically as any other disease, and is not associated with any physical or chemical agent except the use of tobacco."〔 There were however problems and confusion in applying this definition.〔 At a second international symposium held in 1994 it was argued that whilst tobacco was a likely causative factor in the development of leukoplakia, some white patches could be linked directly to the local effects of tobacco by virtue of their disappearance following smoking cessation, suggesting that this kind of white patch represents a reactive lesion to local tissue irritation rather than a lesion caused by carcinogens in cigarette smoke, and could be better termed to reflect this etiology, e.g. smokers' keratosis.〔 The second international symposium therefore revised the definition of leukoplakia to: "a predominantly white lesion of the oral mucosa that cannot be characterized as any other definable lesion." This description is supported by the World Health Organization.〔 The term has been incorrectly used to describe white patches of any cause (rather than specifically referring to idiopathic white patches) and also to refer only to white patches which have a risk of malignant transformation.〔 It has been suggested that leukoplakia is an unhelpful term since there is so much inconsistency surrounding its use,〔 and some clinicians now avoid using it at all.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Leukoplakia」の詳細全文を読む スポンサード リンク
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