ARTICLE
A diagnosis of porokeratosis of Mibelli was made based on
the clinical appearance and histological examination of a biopsy specimen.
Histologically, the epidermis showed a slight acanthosis with invaginations
filled with columns of parakeratosis, forming the cornoid lamella, next
to the orthokeratotic stratum corneum of the adjacent epidermis (Fig.
3). Immunohistochemical staining of dermal inflammatory infiltrate
below the cornoid lamella (CD 3, CD 4, S-100 protein) showed that most
cells were helper T lymphocytes with some intermingled Langerhans cells.
The lesions regressed partially with lubrication and keratolytic
treatment but afterwards relapsed. No lesion suggesting malignant degeneration
was found.
Porokeratosis is a dermatosis which results from a specific
alteration of keratinization [1].
Five clinical types of porokeratosis are known:
1. Classic porokeratosis of Mibelli.
2. Disseminated superficial porokeratosis and disseminated
superficial actinic porokeratosis.
3. Porokeratosis palmaris et plantaris disseminata.
4. Linear porokeratosis.
5. Punctate porokeratosis.
It has been postulated that porokeratosis
results from proliferation of an abnormal cellular clone to which several
trigger factors have been suggested: irradiation, infective agents, trauma
and immunosuppression [2]. Mibelli's porokeratosis has occasionally been
described following immunosuppression [3]. Nevertheless, none of those
factors was apparently implicated in our clinical case. The aetiology
is still unknown but it has been suggested that the presence of helper
T cells and some Langerhans cells in Mibelli's porokeratosis, as in this
present case, is evidence for immunological mechanisms induced by antigen
presentation [4].
Porokeratosis of Mibelli (classic) is a rare disease, which
frequently appears at an early age. It can be inherited, as an autosomal
dominant character, or sporadic [2], with a higher incidence in males.
The usual clinical presentation of this disease is keratotic
papules of various sizes, which may coalesce in plaques with irregular
boundaries, characterised by a raised border with a well defined longitudinal
furrow. The lesions are generally unilateral, involving predominantly
the distal part of the limbs, thighs and perigenital region, although
they may also appear on other parts of the body [1]. In this case we had
some combination features of several porokeratosis types: the bilateral
distribution of porokeratosis palmaris et plantaris disseminata (without
hand involvement), a linear boundary on the sides of the feet suggests
linear porokeratosis and punctiform lesions on the soles are like punctate
porokeratosis.
Malignant transformation in porokeratosis lesions is more
frequent on non-exposed skin [2], over the extremities [5] and with an
average latency period of 36 years (shorter in porokeratosis of Mibelli)
[2]. In spite of those areas being affected in our patient and the long
duration of disease about 32 years no lesion suggesting
malignant degeneration was found in the follow up.
In accordance with the clinical aspects discussed above,
we suppose we are describing an unusual case of porokeratosis, with uncommon
characteristics when compared with those reported in the literature.
Article accepted on 22/5/00
REFERENCES
1. Elisabeth C, Wolff-Schreiner. Porokeratosis. In:
Fitzpatrick's Dermatology in General Medicine. 1999; fifth edition, McGraw
Hill, pp. 624-30.
2. Schamroth JM, Zlotogorski A, Gilead L: Porokeratosis
of Mibelli. Overview and review of the literature. Acta Derm Venereol
(Stockh) 1997; 77: 207-13.
3. Wilkinson SM, Cartwright PH, English JSC. Porokeratosis
of Mibelli and immunosuppression. Clinical and Experimental Dermatol
1991; 16: 61-2.
4. Jurecka W, Neumann RA, Knobler RM. Porokeratoses:
immunohistochemical, light and electron microscopic evaluation. J Am
Acad Dermatol 1991; 24: 96-101.
5. Mehregan AH, Khalili H, Fazel Z. Mibelli's porokeratosis
of the face. J Am Acad Dermatol 1980; 3: 394-6.
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