Microscopic Findings

Histopathological examination of a punch biopsy taken from the annular edge of one lesion from the left side of the nose showed mild hyperkeratosis of the stratum corneum, [Figure 2] and [Figure 4] with a parakeratotic column (cornoid lamella) overlying a follicular infundibulum [Figure 3] and [Figure 5]. The epidermis beneath the cornoid lamella exhibited agranulosis with an occasional apoptotic keratinocyte. There was a superficial perivascular and perifollicular infiltrate of lymphocytes and histiocytes. The basement membrane was uninvolved.

Figure 2: Column of parakeratosis (cornoid lamella) arising from the infundibulum of a hair follicle (H and E, ×100) Click here to view

Figure 3: A cornoid lamella tier arising from a follicular infundibulum (H and E, ×20) Click here to view

Figure 4: Low power view (×40a) Click here to view

Figure 5: Medium power view with more dermis seen (×100a) Click here to view

Diagnosis

Localized actinic porokeratosis.

Discussion

Porokeratosis is a group of epidermal keratinization disorders clinically characterized by an extending keratotic lesion with an atrophic centre bordered by a peripheral keratotic ridge. The hallmark histopathological feature is a parakeratotic column called the cornoid lamella. The two most common forms of porokeratosis are classic porokeratosis of Mibelli (PM) and disseminated superficial actinic porokeratosis (DSAP). Although facial lesions are seen in 15% of patients with DSAP, ^[1] exclusive facial porokeratosis is rare with 40 case reports in the literature.

Facial porokeratosis predominantly affects young women and from the single largest published series of facial porokeratosis (15 patients), ^[2] it was also noted that most of them had nasal or perinasal lesions which worsened with sunlight exposure. This might represent a distinct subset of PM related to actinic damage, and the term localized actinic nasal porokeratosis had been suggested. ^[3]

It was postulated that porokeratosis arises from a mutant clone of epidermal cell, but the exact pathogenesis is not understood. Some possible theories include faulty maturation, such as early keratinocyte apoptosis with dysregulation of terminal differentiation, and overexpression of p53. ^[4] This condition may be sporadic in onset or inherited in an autosomal dominant manner. Although the risk of malignant transformation of porokeratosis has been reported to be between 7.5% and 11%, ^[5] malignant degeneration has not been observed in facial porokeratosis.

Many different treatment modalities have been used to treat facial porokeratosis, including keratolytics, topical 5-fluorouracil, topical imiquimod, oral and topical retinoids, lasers, cryotherapy, and dermabrasion. However, response to treatment is variable and relapses have been observed after cessation of treatment.

Our patient was treated with topical imiquimod with minimal improvement. It has been thought that immunosuppression might favor the development of porokeratosis. Imiquimod activates the immune system through agonistic activity toward toll-like receptors 7 and 8, which then activates nuclear factor-kappa B, resulting in the induction of pro-inflammatory cytokines and chemokines, leading to activation of the innate immune system and mounting a T-helper 1 cellular immune response. ^[6] To date, there is no consensus on the management of this condition.

Learning Points

1. Porokeratosis is a group of epidermal keratinization disorders clinically characterized by an extending keratotic lesion, with an atrophic center bordered by a peripheral keratotic ridge.
2. The hallmark histopathological feature is a parakeratotic column called the cornoid lamella.
3. Most lesions are seen on the extremities of limbs and rarely on the face.