Leukokeratosis vs. Leukoplakia

Differential Diagnosis

Leukokeratosis Leukoplakia 1. Orthokeratosis with few parakeratotic cells 1. Parakeratosis with few orthokeratotic cells 2. Hypergranulosis 2. Few, if any, granular cells in a lesion that has not been rubbed persistently 3. Epithelium thickened slightly 3. Epithelium thickened considerably 4. No abnormal keratocytes 4. Abnormal keratocytes 5. No mitotic figures 5. Mitotic figures usually 6. No dyskeratotic cells 6. Many dyskeratotic cells 7. Slight perivascular infiltrate of mononuclear inflammatory cells 7. Moderately dense perivascular infiltrate of mononuclear inflammatory cells

Discussion

Leukokeratosis and leukoplakia are white, slightly elevated nonindurated lesions of the mucosae (especially of the mouth, but also of the vagina and other areas) that also have some attributes histopathologic in common, namely, hyperkeratosis, a thickened epithelium, and an infiltrate of mononuclear cells. The white color (leuko-) in both leukokeratosis and leukoplakia results from abnormal production and maceration of cornified cells. But the essential character of the two conditions is polar: leukokeratosis is lichen simplex chronicus, a result of rubbing persistent for many months and even years, whereas leukoplakia is squamous-cell carcinoma.

The main difference histopathologic between the two conditions lies in the nuclei of the keratocytes that compose them, those in leukokeratosis being "typical" and those in leukoplakia being decidedly "atypical," i.e., large, hyperchromatic, and pleomorphic, some of them often in mitosis. We advocate the use of the term leukoplakia for those white lesions on mucous membranes that are squamous-cell carcinoma, just as we are in accord with the designations "solar keratosis" and "Bowen's disease" for other types of squamous-cell carcinoma. Like solar keratosis and Bowen's disease, leukoplakia is simply a superficial squamous-cell carcinoma. The cause of oral leukoplakia is not identifiable in every instance, but smoking and chewing of tobacco surely are factors in many a patient. Another white lesion of mucous membranes that may present a problem of differential diagnosis clinically is candidiasis, but there the cornified layer teems with hyphae.

The importance of making a definite diagnosis of leukoplakia is that a neglected lesion may progress to become large enough and deep enough to be destructive locally and to metastasize.

In contrast, leukokeratosis oris is a wholly innocuous condition that may revert to normal mucous membrane when the cause of it is removed. The most common cause of leukokeratosis oris is persistent trauma or friction by dentures, maloccluded teeth, or habitual biting of the lips or buccal mucosa. In short, leukokeratosis is simply lichen simplex chronicus on mucous membranes.

The abnormal nuclei in leukoplakia, like those in its cutaneous analogues, i.e., solar keratosis arsenical keratosis, radiation keratosis, reside mostly in the lower portion of the epithelium. In contradistinction to the squamous-cell carcinoma of erythroplasia of Queyrat, (Bowen's disease), abnormal nuclei of keratocytes are present throughout most or all of the thickened epithelium. As long as the abnormal keratocytes are confined an epithelium of mucous membranes and of epidermis that is superficial, as they are in leukoplakia, solar keratosis, radiation keratosis, arsenical keratosis, erythroplasia, and Bowen's disease, the process is benign biologically, i.e., it cannot and does not metastasize. Nevertheless, each of those proliferations of abnormal keratocytes should be removed completely in order to prevent eventuation in a deep squamous-cell carcinoma with capability for metastasis. No clinician and no histopathologist, by signs morphologic alone, can predict which lesion uncommon of leukoplakia or solar keratosis will metastasize eventually.

Some lesions clinical of leukoplakia have red zones interspersed among white ones, and still other lesions are mostly red. The name erythroplakia has been given to those mostly red lesions on mucous membranes that, like leukoplakia, are nothing other than a superficial squamous-cell carcinoma and that, if left untreated, may progress to a conclusion fatal. In brief, leukoplakia, erythroplakia, and erythroplasia are squamous-cell carcinomas on mucous membranes. Just as solar keratoses may be mostly white or red clinically depending on the amount of cornification associated with them, so, too, their analogues on mucous membranes, for the same reason, may be mostly white (i.e., leukoplakia) or red (i.e., erythroplakia).

Parenthetically, when a lesion of leukoplakia is rubbed persistently, features of leukokeratosis are likely to be imposed on it. In those instances, abnormal keratocytes, a thickened epithelium, hypergranulosis, and both parakeratosis and compact orthokeratosis will be present together.

Ref:

Differential Diagnosis In Dermatopathology I, Ii, Iii, Iv.chm