Porokeratosis of the lower lip

ARTICLE

The porokeratoses are defined as specific disorders of keratinization that are histologically characterised by the presence of a dense, parakeratotic column, well-circumscribed from the rest of the corneocytes, known as the cornoid lamella. In this article, we report two cases of porokeratosis of the lower lip, drawing attention to the unusual site. We also emphasize the clinical appearance of these lesions, which may easily be misdiagnosed if not examined correctly. As a consequence of this misdiagnosis, the prevalence of these lesions is probably greater than at present estimated. Moreover, a good response to cryotherapy is shown.

Key words: lower lip, Mibelli's porokeratosis, porokeratosis.

The porokeratoses are specific disorders of keratinization. They are histologically characterised by the presence of a dense parakeratotic column, well-circumscribed from the rest of the corneocytes, and known as the cornoid lamella. These lesions are due to clones of cells which show varying degrees of dysplasia and may eventually evolve to neoplasia [1].

In this article we present two cases of porokeratosis of the lower lip, emphasizing two aspects: the site, which apart from being exceptional, poses problems of differential diagnosis with other fixed white patches or plaques, and a good response to cryotherapy.

Case reports

Case 1

A 50-year-old woman was referred to our department in 1993 complaining of an oval whitish plaque (2.3 cm by 1.3 cm), with an atrophic centre and slightly hyperkeratotic edge on her lower lip (Fig. 1). A biopsy of the edge of the lesion showed an atrophic epidermis with hyperkeratosis and a parakeratotic column at the periphery. In the dermis there was basophilic degeneration of the collagen fibres and slight inflammatory infiltration (Fig. 2). A histologic diagnosis of porokeratosis was made and the lesion was considered to be a single plaque of Mibelli's porokeratosis. Some months later numerous erythematous lesions appeared with a centrofacial distribution. They had a thin keratotic edge 2 to 3 mm in diameter, and were clinically diagnosed as actinic porokeratosis (Fig. 3). The patient had no other lesions on her body and no relevant family history. All the lesions were treated with cryotherapy with a good response. Some of the non-labial lesions relapsed.

Case 2

The second patient was seen in our department in November 2000. She was a 38-year-old woman with a history of relapsing herpes labialis. She complained of an asymptomatic lesion on her lower lip present for eight months. Examination revealed a 1.5 by 0.7 cm plaque, with a continuous linear keratotic edge, and an atrophic centre which was smooth and whitish-yellow (Fig. 4).

She had no other lesions on her skin or mucous membranes. There was no family history of skin diseases. Histological examination of the lesion was similar to that of the previous case, showing an atrophic epidermis with hyperkeratosis, the presence of a cornoid lamella (Fig. 5), no atypical cells and basophilic collagen degeneration in the dermis. All these findings were compatible with the diagnosis of porokeratosis. The patient is still being treated with cryotherapy, with good results.

Discussion

Porokeratosis is a not uncommon pathological disorder. The lesion of porokeratosis consists of an atrophic centre bordered by a peripheral grooved keratotic ridge. If the biopsy is taken from the periphery of the lesion, the typical features can be seen. These consist of a keratin-filled epidermal invagination with an angulated parakeratotic tier, the cornoid lamella. The epithelium below the tier is vacuolated and devoid of granular thin layer. Dyskeratotic cells may be present and epidermal dysplasia is occasionally a feature. There are various forms of porokeratosis. Disseminated superficial actinic porokeratosis is characterised by numerous small, dry shallow lesions arising on the sun-damaged skin of adults. It presents in the third and fourth decades and despite its relationship to sunlight rarely affects the face. The legs and forearms are most commonly affected. Disseminated superficial non-actinic porokeratosis is characterised by asymptomatic lesions with a tendency to involve the trunk, genitalia, palms and soles. In linear porokeratosis, the lesion is clinically reminiscent of an epidermal naevus and usually presents in infancy or early childhood. Punctate porokeratosis involves particularly the palms and soles. The classical form of Mibelli consists of a single plaque, or a small number of plaques, of variable size of up to a few centimetres. Although any part of the body may be affected, including the palms, soles and mucous membranes, it is usually seen on the limbs and genitalia. A solitary plaque of porokeratosis is exceptionally seen on the lips. Only three such cases have been reported in the past forty years [2, 3]. There is a reported case of bilateral, symmetrical involvement of the labial commissures [4]. The lesions of labial porokeratosis in our two patients were very similar. Their aspect was that of porokeratosis of Mibelli at an unusual site. However, the presence of lesions at other sites on the face of one of our patients suggests a diagnosis of actinic porokeratosis, which leads to problems of terminology. Nevertheless, co-existence of various types of porokeratosis in the same patient have been described previously [1, 5].

At the time of examination, we must pay attention to detect a delicate, but well-defined hyperkeratotic edge delimiting the lesion. Also, this rare presentation of a single lesion should lead to a clinical differential diagnosis especially with atrophic annular lichen planus and actinic cheilitis. Skin biopsies will help to make the diagnosis, because the histology is pathognomonic. However, if careful clinical examination is not made, the hyperkeratotic edge may be overlooked and biopsies may be performed inappropriately from the centre of the lesion and the diagnosis may be missed.

Cryotherapy worked in our two patients, and as this treatment has already been proved successful [6], we think that cryotherapy may be useful in similar cases.

We consider that if this location of the lesion is kept in mind, more cases of the disorder may be found and it may be proved to be more common than is currently thought.

References

1. Lucker GP, Steiljen PM. The coexistence of linear and giant porokeratosis associated with Bowen's disease. Dermatology 1994; 189: 78-80.

2. Dupre A, Christol B. Mibelli's porokeratosis of the lips. Arch Dermatol 1978; 114: 1841-2.

3. Schnitzler L, Verret JL, Baudoux C. Porokératose de Mibelli de la lèvre. Ann Dermatol Venereol 1978; 105: 749-50.

4. Kanitakis C, Ktenides M, Tsoitis G. Porokératose de Mibelli des lèvres bilatérale et symétrique. Dermatologica 1981; 163: 1-4.

5. Shimamoto Y, Shimamoto H. Differentiation of disseminated superficial actinic porokeratosis from the superficial disseminated eruptive form of porokeratosis of Mibelli. Cutis 1988; 42: 345-8.

6. Bhushan M, Craven NM, Beck MH, Chalmers RJ. Linear porokeratosis of Mibelli: successful treatment with cryotherapy. Br J Dermatol 1999; 121: 389.