A patient, aged 37 years, presented with complaints of a scaly spot on his scrotum. The patient reported the spot had been present his whole life.
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Porokeratosis is a disorder of keratinization clinically characterized by hyperkeratotic atrophic plaques that are surrounded by a distinctive raised thin ridgelike border or cornoid lamella.
Several variants of porokeratosis have been described, and all forms present with the characteristic raised edge of the cornoid lamella. The formation of the cornoid lamella is due to the clonal proliferation of keratinocytes.1 All porokeratosis variants (with the exception of the punctate form) are associated with malignant epithelial neoplasms, most commonly squamous cell carcinoma.
Risk factors for porokeratosis include ultraviolet radiation and immunosuppression. The disorder is classified as a genetically heterogeneous as genetic inheritance has been found to play a large role in most of the variants; several chromosomal loci have been discovered, and most forms of the disorder can be inherited in an autosomal dominant pattern.
Porokeratosis of Mibelli is the classic form and the second most common form of porokeratosis. It is seen in about a third of cases.1 Often appearing in childhood, it presents as skin-colored or brown papular lesion with a distinct raised border; the center of the lesion can be variable and can appear hyperpigmented, hypopigmented, scaly and atrophic, anhydrotic, and hairless.
Classically, a thin furrow can be seen running along the center of the ridge surrounding the lesion. The lesions are asymptomatic or mildly pruritic.
Although most commonly found on the extremities, lesions can occur anywhere, including the palms, soles, genitalia, or mucous membranes.1 An autosomal dominant pattern of inheritance is a common etiology.
Disseminated superficial actinic porokeratosis (DSAP) is the most common form of porokeratosis and accounts for half of all cases.1 Lesions in DSAP are characterized as small, uniform, circular papules that are symmetrically distributed and more widespread than other variants of porokeratosis, though the palms, soles, and mucous membranes are spared.
The characteristic raised border of porokeratosis surrounds the lesions, but is more subtle in DSAP compared to porokeratosis of Mibelli. The lesions are found in the areas of greatest sun exposure.
A genetic etiology is common with inheritance following an autosomal dominant pattern and becoming fully penetrant in the third or fourth decade of life.1 Women are affected more so than men.
Linear porokeratosis is a less common variant and is characterized as a mosaic or segmental form of porokeratosis.1,2
Porokeratosis palmaris et plantaris disseminata is characterized by small uniform lesions distributed symmetrically that initially develop on the palms and soles. Compared to other forms of porokeratosis, the lesions tend to be more keratotic and the raised ridge surrounding the lesions more pronounced.
Typically presenting in early adulthood, the lesions may spread and take on a more generalized distribution over time. An autosomal dominant pattern of genetic inheritance is often found and males are more likely to be affected than females.
Treatment of porokeratosis is often unnecessary; the lesions are usually slowly progressing and often asymptomatic or mildly pruritic. However for more serious presentations or for cosmetic reasons, topical retinoids, topical steroids, or keratolytics can be used and ablative measures taken to prevent recurrence.
Surveillance for malignancy is key – especially in patients with giant lesions or linear lesions.
Nrithya Sundararamanis a medical student at Baylor College of Medicine.
Adam Rees, MD, a graduate of the David Geffen School of Medicine at UCLA, practices dermatology in Los Angeles.
- Spencer, L. Porokeratosis. 26 October 2012. Medscape. Retrieved from http://emedicine.medscape.com/article/1059123-overview#a0104
- O’Regan GM, Alan D. I. Chapter 52. Porokeratosis. In: Goldsmith LA, Katz SI, Gilchrest BA, Paller AS, Leffell DJ, Wolff K. eds. Fitzpatrick’s Dermatology in General Medicine, 8e. New York, NY: McGraw-Hill; 2012.
All electronic resources were accessed March 5, 2015