Sir, leukoplakia is a common lesion observed in clinical practice and the term is familiar to the majority of dentists. But a review of the literature reveals that there is considerable ambiguity in the interpretation and use of the term leukoplakia.

In 1978, a World Health Organization (WHO) group defined oral leukoplakia as: 'A white patch or plaque that cannot be characterised, clinically or pathologically as any other disease.' The accompanying text emphasised that the term leukoplakia should carry no histological connotation and should be used only in a descriptive clinical sense. In addition, it was also mentioned that this proposed definition is rather a negative definition and the need for revision and refinement of this definition should be done in the future with increasing knowledge1.

At the international seminar held in 1983, the outcome of which was published in 19842 a new definition was proposed as 'Leukoplakia is a whitish patch or plaque that cannot be characterised clinically or pathologically as any other disease and it is not associated with any physical or chemical causative agent except the use of tobacco.'

Another new definition of leukoplakia was proposed at the International Symposium in Sweden 19943 as 'A predominantly white lesion of the oral mucosa that cannot be characterised as any other definable lesion, some oral leukoplakias will transform into cancer'. The rationale for proposing this new definition was made on the basis of following difficulties in interpretation of previous definitions by WHO in 1978 and Axell in 1984.

The word 'pathologically' in the description of leukoplakia is sometimes interpreted to imply that the diagnosis cannot be made without a biopsy.

Even after careful clinical and histopathological examination, there are some white lesions for which doubt remains as to whether they fall into the category of leukoplakia or any other. Also, the extent to which it is possible to apply adjunctive tests to biopsy material to exclude other diseases varies from laboratory to laboratory. An association with physical or chemical causative agents is difficult to assess and the possibility of a coincidental association cannot readily be eliminated.

Several tobacco-induced lesions, such as leukokeratosis nicotina palatinae, palatal keratosis in reverse smokers and 'snuff dipper's lesion,' are not traditionally described as leukoplakias even though they are partly white and associated with the use of tobacco.

Difficulty was experienced because of the subjective nature of the degree of whiteness of the mucosa required before a diagnosis of leukoplakia should be made. Some authors attempted to overcome this by defining certain lesions as 'pre-leukoplakia.' The condition described as 'leukoedema' may also present problems in this respect. The lesion described as having leukoplakia and associated with immunocompromised patient, particularly those who are HIV positive, has introduced a complication in terminology. It could now be classified as a diagnosable disease and as such, the use of the word 'leukoplakia' in its title is confusing.

Many reports in the literature do not specify whether a diagnosis of leukoplakia has been reached on the basis of a clinical examination alone or after the histopathological report on a biopsy.

Earlier definitions of leukoplakia included the criteria in relation to size (> 5 mm) which does not have any significance. In spite of identification of these difficulties recent text books4,5 still advocate the use of the WHO definition of 1978 while journals advocate use of new definitions. This ambiguity poses a risk of misinterpretation of the patient's record and publications. Therefore, I believe there is a need for standardisation of the definition for better clarity and understanding to avoid confusion.