Keratoacanthoma Arising Over Margin of Porokeratosis of Mibelli: A New Association?

Sir,

Keratoacanthoma is an epithelial tumor characterized by rapid growth with a relatively benign course. Though the exact pathogenesis is unknown, various inciting events and underlying dermatoses were described with the cases of keratoacanthoma.[1] On the other hand, porokeratosis is a disorder of keratinization with a low tendency to the secondary neoplasm.

A 70-year-old male, a farmer by occupation, presented to us with multiple asymptomatic nodules, rapidly arising over the left ankle joint for last 6 months. According to the patient, the lesion started over a plaque that was present since his childhood. On examination, a plaque of 12 cm × 15 cm size was present over the anterior and lateral aspect of left ankle joint. The lesion had an irregular keratotic border with longitudinal furrow and central flat, atrophic area, and beside that there were similar looking lesions over left hand also [Figure 1]. A few pink-colored, cup-shaped nodules with central craters were present on the posterolateral margin of the lesion over left foot [Figures 1 and 2]. In addition, there were multiple keratotic cutaneous horn-like nodules on the anterior side of the plaque [Figure 1]. The son accompanying the patient had similar flat plaques distributed all over the body. General survey, thorough systemic examination, and routine investigations did not reveal any abnormality. We performed an incisional biopsy of a crateriform nodule and a 4 mm punch biopsy each from the border of the porokeratotic plaques in the patient and his son. The histopathology of the nodule had marked hyperkeratosis with a central keratin-filled crater with buttressing of the edges of the crater, prominent acanthosis, and horn cyst [Figure 3a–d]. There was no atypia or other features of malignancy. The two punch biopsy specimens showed similar features with cornoid lamella and the absence of granular cell layer beneath the parakeratotic column [Figure 4]. On the basis of the benign course of the presenting lesion and clinicopathological features, the diagnosis of keratoacanthoma arising over the lesional margin of familial porokeratosis of Mibelli was made.

Figure 1

A porokeratotic plaque over left ankle joint with cutaneous horn-like structures at anterior side and keratoacanthoma at posterolateral margin, and another porokeratotic lesion on the left hand

Figure 2

Double-edged border of porokeratosis of Mibelli with keratoacanthoma at the margin

Figure 3

(a) Central keratin-filled crater is overlying an invaginating acanthotic epidermis (H and E, ×40). (b and c) Buttressing at the ends of the invagination (H and E, × 40). (d) Magnified view of the margin of a horn cyst (H and E, ×100)

Figure 4

Parakeratotic column (cornoid lamella) with the absence of underlying granular cell layer (H and E, ×100)

Keratoacanthomas are exoendophytic lesions with an invaginating mass of keratinizing, well-differentiated squamous epithelium present at the sides and bottom of the lesion. There is a central keratin-filled crater which enlarges with the maturation as well as the evolution of the lesion. Another diagnostic feature is the lipping or buttressing of the edges of the lesion which overlap the central crater, giving it a symmetrical appearance. Epithelial atypia and mitoses are not usual features. There may be a moderately heavy mixed infiltrate of inflammatory cells in the adjacent dermis, and this is often moderately heavy. Histological features which favor a diagnosis of keratoacanthoma over squamous cell carcinoma (SCC) include the characteristic low-power architecture with a flask-like configuration and central keratin plug, as well as the pattern of cell keratinization with large central cells with eosinophilic cytoplasm.[2]

The exact etiopathogenesis of keratoacanthoma is unclear; however, suspected inciting factors include ultraviolet light, genetic factors, immunosuppression, chemical carcinogens, viruses, various types of mechanical trauma, or it may arise secondary to other skin lesions such as psoriasis, discoid lupus erythematosus, herpes zoster, lichen planus, seborrheic dermatitis, pemphigus foliaceus, and others.[134]

Porokeratosis is a rare disorder of keratinization characterized clinically by a hyperkeratotic ridge on the border and histopathologically by a stack of parakeratosis (cornoid lamella) overlying an absent granular cell layer.[2] Porokeratosis of Mibelli usually begins during infancy or childhood. Inheritance is usually autosomal dominant. Hypertrophic, cutaneous horn-like lesions localized mostly to the periphery of a lesion in porokeratosis have been described.[5]

SCC is the most commonly reported malignancy in porokeratosis. Other associated neoplasms reported are Bowen's disease, basal cell carcinoma, diffuse large B-cell lymphoma, and others.[56] However, to the best of our knowledge, till date, no case of keratoacanthoma has been reported to appear over porokeratosis of Mibelli in the Medline journals. Hence, we would like to conclude that beside other neoplasms, keratoacanthoma can also occur as a secondary change on porokeratosis.

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Conflicts of interest

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