Porokeratosis Workup

Updated: Oct 09, 2020
  • Author: Amarateedha Prak LeCourt, MD; Chief Editor: William D James, MD  more...
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Laboratory Studies

Generally, no laboratory studies are required. Screening for diseases causing immunosuppression (eg, HIV, hematologic malignancies) and/or renal failure is appropriate when new lesions of classic porokeratosis of Mibelli (PM) or disseminated superficial porokeratosis (DSP) are seen or when sudden exacerbation of any form of porokeratosis develops.


Histologic Findings

The cornoid lamella is the histopathologic hallmark of all forms of porokeratosis. It is essential that a biopsy specimen be taken from the peripheral, raised, hyperkeratotic ridge to demonstrate this finding.

The cornoid lamella consists of a thin column of tightly packed parakeratotic cells within a keratin-filled epidermal invagination. The parakeratotic column extends at an angle away from the center of the lesion and develops from the interfollicular epidermis, but it may involve the ostia of hair follicles or sweat ducts. Within the parakeratotic column, the horny cells appear homogeneous and possess deeply basophilic pyknotic nuclei. In the epidermis beneath the parakeratotic column, the keratinocytes are irregularly arranged and have pyknotic nuclei with perinuclear edema. No granular layer is seen within the parakeratotic column, while the keratin-filled invagination of the epidermis has a well-developed granular layer.

The papillary dermis beneath the cornoid lamella contains a moderately dense, lymphocytic infiltrate and dilated capillaries. Dermal amyloid deposits have been described in some cases of disseminated superficial actinic porokeratosis (DSAP). They have also been described in the intertriginous portion of porokeratosis ptychotropica, suggesting a role for friction in pathogenesis of this variant of PM. [65]

Specimens taken from the center of the lesion show atrophy, with areas of liquefaction degeneration in the basal layer, colloid-body formation, and flattening of rete ridges. The dermis may be edematous or fibrotic with telangiectasia. Amyloid deposition may be seen in the papillary dermis, both centrally and beneath the cornoid lamellae. The cornoid lamella is prominent in PM but less distinct in DSAP, DSP, and porokeratosis palmaris et plantaris disseminata (PPPD). At the ultrastructural level, vacuolization of keratinocytes, clumping of keratin filaments, and a paucity of lamellar bodies are found. Intercellular lamellar sheets are incompletely formed and may be responsible for defective desquamation.

Immunohistochemical studies show that keratinocytes beneath the cornoid lamella stain in a pattern similar to that observed in squamous cell carcinomas. The parakeratosis appears to be the result of faulty maturation of keratinocytes, rather than an increased rate of proliferation. [11] Keratinocytes central to the cornoid lamella stain in a pattern identical to that of premalignant lesions, such as actinic keratosis. Keratinocytes peripheral to the cornoid lamella stain normally.

Recent studies showing reduced bleomycin hydralase expression in porokeratosis lesions support the hypothesis that the pathogenesis of porokeratosis involves a defect in the late stage of epidermal differentiation. [12]