Porokeratoses – chronic cornification disorder of the epidermis

Clinically, porokeratoses are characterized by a keratinization disorder. Several porokeratosis variants are distinguished. A common histologic feature of all porokeratoses is corneal lamellae in the marginal ridge area. Due to the risk of malignant degeneration, consistent sun protection and regular clinical controls are recommended.

The cornification disorder in the context of porokeratosis is accompanied by scaly or nodular skin changes of the epidermis. The corneal lamella seen in histopathology (Fig. 1) corresponds clinically to the hyperkeratotic margin of porokeratosis [1]. More specifically, it is a slit-shaped hyperkeratotic horny ridge embedded in the epidermis in marginal zones of the lesions [2]. The classification of the different porokeratoses is based on features of the clinical morphology, due to the topography of the morphs and the age of manifestation, among other factors [2].

What are the most common forms?

The best known is the so-called porokeratosis mibelli, which usually occurs in childhood and adolescence, but sometimes only in older adulthood. If the hands are affected, the nails close to the heart may be affected (nail dystrophy with longitudinal rippling of the nail plate). Porokeratosis linearis also usually manifests in childhood. Characteristic are multiple smaller, isolated standing or confluent foci of hyperkeratotic papules in linear or zosteriform arrangement predominantly on one side of the distal extremities [3]. In disseminated superficial porokeratosis , itchy, flat, often anular papules and plaques are found, often actinically triggered (porokeratosis superficialis disseminata actinica) [4]. Porokeratosis superficialis disseminata actinica typically manifests as numerous disseminated lesions in light-exposed areas, especially on the dorsum of the hand, the extensor sides of the forearm, but also on the face. Mostly women of higher age are affected. [3]. Furthermore, there are some rarer special forms of porokeratoses.

Porokeratoses are considered to be premalignant skin lesions

Case reports, case series, and reviews have described an association of porokeratoses with malignancies [5]. Consequently, squamous cell carcinoma (SCC) forms most frequently, while basal cell carcinoma is less common. A registry study published in JEADV in 2023 collected epidemiologic data on porokeratoses and skin cancer risks [5] (box). The frequency with which malignant transformation and non-melanocytic skin cancer develops from porokeratoses is reported in the literature to be 6.9-30% [6–8]. Pathophysiological explanations for the observed association between porokeratoses and skin cancer incidences are not yet known [5].

What treatment options are known?

Several approaches exist for the treatment of porokeratoses, including topical, systemic, and surgical therapeutic options. However, due to the lack of randomized-controlled trials, there are no international treatment guidelines to date [9].

• In porokeratosis mibelli , the use of imiquimod cream has proven most successful.
• Porokeratosis linearis shows a good response to both topical and systemic retinoids [9].
• The most promising therapeutic option for disseminated superficial porokeratosis is topical vitamin D3 derivatives [9].

Surgical intervention or cryotherapy may be considered for areas not suitable for topical treatment [9]. The use of laser-based procedures is another treatment option [10]. Topical steroids, retinoids, and topical diclofenac can relieve symptoms [6]. However, no sustained therapeutic effect is expected [6]. Furthermore, topical lovastatin improved symptoms in a small study [11].

Literature:

1. Wikiderm, https://www.wikiderm.de/Kompendium/Porokeratosis,(last accessed May 27, 2023).
2. Kowalzick L, et al: Dermatology from case to case. Chapter 11 – Nevi, nevoid lesions, and benign tumors. Porokeratosis linearis unilateralis. Thieme 2013. DOI: 10.1055/b-0034-57887
3. Hereditary keratinization disorders of the skin, www.springermedizin.de/emedpedia/histopathologie-der-haut/hereditaere-verhornungsstoerungen-und-epidermale-fehlbildungen?epediaDoi=10.1007%2F978-3-662-44367-5_20,(last accessed May 27, 2023).
4. Porokeratosis mibelli, www.altmeyers.org/de/dermatologie/porokeratosis-mibelli-3173,(last accessed May 27, 2023).
5. Inci R, et al: Porokeratosis is one of the most common genodermatoses and is associated with an increased risk of keratinocyte cancer and melanoma. JEADV 2023; 37(2): 420-427.
6. Joshi R, Minni K: Genitogluteal porokeratosis: a clinical review. Clin Cosmet Investig Dermatol 2018; 11: 219-229.
7. Leow YH, Soon YH, Tham SN: A report of 31 cases of porokeratosis at the National Skin Centre. Ann Acad Med Singap 1996; 25(6): 837-841.
8. Ahmed A, Hivnor C: A case of genital porokeratosis and review of literature. Indian J Dermatol 2015; 60(2): 217.
9. Weidner T, et al: Treatment of Porokeratosis: A Systematic Review. Am J Clin Dermatol 2017; 18(4): 435-449.
10. Le C, Bedocs PM: StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 8, 2022. Disseminated Superficial Actinic Porokeratosis.
11. Atzmony L, et al: Topical cholesterol/lovastatin for the treatment of porokeratosis: A pathogenesis-directed therapy. JAAD 2020; 82(1): 123-131.

DERMATOLOGIE PRAXIS 2023; 33(3): 36