Porokeratosis of Mibelli - Not So Rare in Coloured Skin.

Sir,

The reported clinical presentations[1] including the current one dispel the traditional belief that porokeratosis of Mibelli (PM) is rare in colored people[2] as compared to Caucasians.

A 41-year-old man presented with multiple raised annular plaques that started in childhood over the left lower limb including the thigh, leg, buttock, and later the sole associated with moderate itching. Over time they enlarged, became gyrate, and appeared on the nail, face, back, and glans penis. They were bordered by a serpentine keratotic ridge with a distinct central furrow, appreciable even in small lesions. The central area was slightly atrophic and hypopigmented. His grandmother, father, and aunt were affected and had appeared in his 24-year-old son in childhood [Figure 1a] Dermoscopy revealed a white rim corresponding to the central furrow enclosing whitish brown dots, the furrow being well appreciated in the sole lesion. Thinning and a broad longitudinal split were seen in the middle of right thumbnail with the lesion extending to paronychium [Figure 1b]. Histopathology revealed the characteristic cornoid lamella composed of stacked parakeratotic layers arising from a notch extending deeply at an angle into the epidermis where granular layer was absent and dyskeratotic cells were present. The dermis showed an aggregate of lymphocytes and dilated vessels [Figure 2].

Figure 1

Porokeratosis showing (a) serpentine borders on thigh & son with circular lesion below ear, and (b) central nail dystrophy with paronychial involvement

Figure 2

Cornoid lamella with dyskeratotic cells at base surrounded by a dermal infiltrate of lymphocytes (HE ×20)

An autosomal dominantly inherited genodermatosis of incomplete penetrance, PM is classic among the five well-known morphological presentations of porokeratosis. All are characterized histopathologically by the proliferation of an abnormal clone of keratinocytes forming the cornoid lamella. Best appreciated in PM, it is picturesquely described clinically to resemble the “Great wall of China.” PM appears in childhood and predominantly affects males, characterized by slowly enlarging plaques often appearing on one limb and spreading later to other areas including mucosa and uncommonly the nails. Visualizing the furrow within the keratotic border by noninvasive techniques like dermoscopy and other high-resolution imaging procedures helps in distinguishing it from other dermatoses, yet biopsy is needed for confirmation.[3] The presentation in our patient, appearing unilaterally and later disseminating, is similar to that first described by Mibelli in 1893, which has been reinterpreted as an early example of type 2 segmental manifestation of an inherited dermatosis.[4] Sporadic cases arising from somatic mutations have also been seen. A wide range of nail changes from splitting to dystrophy, shedding, and pterygium have been rarely reported.[5] The etiology of PM remains unclear. The dominant hypothesis is of an abnormal clone of mutant keratinocytes, supported by the finding of aneuploid DNA, giving rise to the cornoid lamella and the increased expression of oncoproteins by the keratinocytes close to the cornoid lamella. Nevertheless, the course of the disease is benign and malignant transformation to squamous cell carcinoma has been rarely reported in giant forms.[3] There being no well-set recommendations, treatments have focused on topical or systemic drugs modifying keratinization, altering the immune response, antiproliferative agents, and irritants to provoke inflammation. Destructive procedures like surgical excision, laser, and cryosurgery have also been used. Usually, a combination of these monitored by the outcome remains the best option.[23]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.