Porokeratosis of Mibelli on the sole

ARTICLE

A 17-year-old patient was referred to our Dermatology Clinic because of an asymptomatic lesion on the left foot. The lesion had appeared during childhood and had grown indolently. On examination, an erythematous, slightly scaly, well-demarcated plaque was observed on the plantar aspect of the left foot. The lesion had an irregular and elevated border and a longitudinal furrow (Fig. 1). Histology of the lesion is shown in Figure 2.

Porokeratosis of Mibelli on the sole

A biopsy of the edge of the lesion revealed a column of parakeratotic cells extending through the entire thickness of the surrounding orthokeratotic stratum corneum. The epidermis beneath this finding presented some dyskeratotic cells (Fig. 2). The clinical and histological picture was consistent with the diagnosis of porokeratosis of Mibelli. Our patient was treated locally with 5-fluorouracil, keratolytic agents and liquid nitrogen, and orally with etretinate for several weeks without significant improvement. The lesion was removed by total excision and skin graft.

Porokeratosis consists of a disorder of the keratinization process. The classical type of porokeratosis was originally described by Mibelli [1]. Although the etiology of this disease is unknown, Reed and Leone [2] suggested that it could be caused by a mutant clone of epidermal cells which induce the formation of a cornoid lamella. Since the lesion sometimes involves the sweat duct, the disease was termed porokeratosis [1]. The factors which have been reported to induce these lesions include: irradiation, photochemotherapy, immunosuppression and drug reaction to thiazides [1].

Five clinical variants of porokeratosis have been described: (1) classical porokeratosis of Mibelli, consisting of chronic, progressive, hyperkeratotic irregular plaques. They measure from a few mm to several cm, and are present usually in acral areas of the extremities [1]; (2) disseminated superficial porokeratosis, described by Chernosky [3] is characterized by numerous keratotic, ring-like papules confined to sun-exposed areas; (3) porokeratosis palmaris plantaris et disseminata, described by Guss et al. [4] where the lesions are similar to the previous variants, but they are also located in non-exposed areas; (4) linear porokeratosis. In this variant the lesions are similar to the classical form of porokeratosis, but the lesions are grouped in a linear systematized form, similar to linear verrucous epidermal nevus [5]; (5) punctate porokeratosis, consisting of multiple, discrete, hyperkeratotic lesions surrounded by delicate raised margins, on palms and soles [6].

The differential diagnosis in the plaque type of porokeratosis includes elastosis perforans serpinginosa, the superficial disseminated form may resemble solar keratosis, stucco keratosis, flat seborrheic keratosis and flat vurruca [1].

Several treatments have been used including 5-fluorouracil, cryotherapy and electrodissication in the disseminated forms of porokeratosis, but since malignancies such as Bowen's disease and basal cell carcinoma have developed in the plaque type of porokeratosis, total excision of the lesion is recommended.

REFERENCES

1. Wolff-Schreiner EC. Porokeratosis. In: Fitzpatrick TB, Eisen AZ, Wolff K, Freedberg IM, Austen K, eds. Dermatology in general medicine. New York: McGraw-Hill, Inc., 1993 : 565-71.

2. Reed RJ, Leone P. Porokeratosis ­ a mutant clonal keratosis of the epidermis. Arch Dermatol 1970; 101: 340-7.

3. Chenorsky ME. Porokeratosis: report of twelve patients with multiple superficial lesions. South Med J 1966; 59: 289-94.

4. Guss SB, Osbourn RA, Lutzner MA. Porokeratosis plantaris, palmaris et disseminata: a third type of porokeratosis. Arch Dermatol 1971; 104: 366-73.

5. Eyre WG, Carson WE. Linear porokeratosis of Mibelli. Arch Dermatol 1972; 105: 426-9.

6. Rahbari HR, Cordero AA, Mehregan AH. Punctate porokeratosis. A clinical variant of porokeratosis of Mibelli. J Cutan Pathol 1977; 4: 338-41.