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.
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