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One of the most contagious of the oral papillary lesions is focal epithelial hyperplasia or Heck's disease, another HPV-induced epithelial proliferation first described in 1965 in Native Americans. The level of contagion is exemplified by the fact that in some isolated populations up to 40% of children have been affected. Today it is known to exist in numerous populations and ethnic groups and to be produced by one of the subtypes of the human papillomavirus, HPV-13, and possibly HPV-32. Where the infection is endemic among children, adults seem to have minimal evidence of residual oral lesions and so the lesions are presumed to eventually disappear on their own.
Focal epithelial hyperplasia is somewhat different from other HPV infections in that it is able to produce extreme acanthosis or hyperplasia of the prickle cell layer of the epithelium with minimal production of surface projections or induction of connective tissue proliferation. The mucosa may be 8-10 times thicker than normal.
Heck's disease primarily occurs in children, but lesions may occur in young and middle-aged adults. There is no gender predilection. Sites of greatest involvement include the labial, buccal and lingual mucosa, but gingival and tonsillar lesions have also been reported.
Individual lesions are broad based or so slightly elevated as to present as well demarcated plaques (Figure 1). Lesions are frequently papillary in nature (Figure 2), but relatively smooth-surfaced, flat-topped lesions are more commonly seen. Papules and plaques are usually the color of normal mucosa, but may be pale or, rarely, white. Hyperplastic lesions are small (0.3-1.0 cm.), discrete, and well-demarcated, but they frequently cluster so closely together that the entire mucosal area takes on a cobblestone or fissured appearance (Figure 3).
Pathology and Differential Diagnosis
Epithelial hyperplasia in this disease presents microscopically as an abrupt and sometimes considerable focal acanthosis of the oral epithelium. The thickened mucosa extends upward, not down into underlying connective tissues, hence, the lesional rete ridges are at the same depth as the adjacent normal rete ridges. The ridges themselves are widened, often confluent and sometimes club-shaped; they are not long and thin as in psoriasis and other diseases. Some superficial keratinocytes show a koilocytic change similar to that seen in other HPV infections, while occasional others demonstrate a collapsed nucleus which resembles a mitotic figure (mitosoid cell). These presumably result from viral alteration of the cells. Virus-like particles have been noted ultrastructurally within both cytoplasm and nuclei of cells within the spinous layer, and this layer is positive for HPV antigen with in situ hybridization.
The lesion is usually easily differentiated from squamous papilloma, verruca vulgaris and condyloma by its lack of pronounced surface projections; the presence of mitosoid cells, and the lack of connective tissue cores in the surface projections, when present. The sessile nature of focal epithelial hyperplasia also serves to separate it from the former two lesions, although this is not a guaranteed distinction.
Focal epithelial hyperplasia also tends to lack the pronounced elongation of thin rete ridges seen in keratoacanthoma and pseudoepitheliomatous hyperplasia, and it lacks the central keratin-filled core of the keratoacanthoma. It also lacks the subepithelial foamy or granular histiocyte-like cells required for the diagnosis of verruciform xanthoma.
Treatment and Prognosis
Conservative excisional biopsy may be required to establish the proper diagnosis, but additional treatment is unnecessary, except perhaps for esthetic reasons relating to visible labial lesions. Spontaneous regression has been reported after months or years, and the disease is rather rare in adults. No case of focal epithelial hyperplasia has been reported to transform into carcinoma. It should be remembered that focal epithelial hyperplasia may be an oral manifestation of AIDS.
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Viraben R, et al. Focal epithelial hyperplasia (Heck disease) associated with AIDS. Dermatology 1996; 193:261-262.
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