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Porokeratosis is a precancerous disorder of keratinization that classically presents as a papule or plaque with thread-like peripheral scale. There are at least five clinical variants, but all are defined histologically by the presence of cornoid lamellae. Subtypes include (1) Porokeratosis of Mibelli (considered the prototypical lesion, although it is rare), (2) Disseminated superficial porokeratosis and disseminated superficial actinic porokeratosis (a more common variant that typically affects the extremities in adults), (3) linear porokeratosis (which arises in infancy and childhood and follows lines of Blaschko), (4) punctate porokeratosis (affecting the palms and soles), and (5) porokeratosis palmaris et plantaris disseminata (which affects palms, soles, and other areas of the body). Treatment of porokeratosis is challenging and traditionally has focused on destroying the abnormal clone of keratinocytes thought to be responsible for the clinically observed lesion. Choice of treatment modality is dependent on the subtype, extent, and distribution of the lesions. The authors’ preference is for topical therapy with cholesterol and lovastatin for DSAP and topical 5-fluorouracil/calcipotriene in combination for Porokeratosis of Mibelli. Systemic therapy with retinoids is reserved for recalcitrant, highly symptomatic cases or cases with high risk of squamous cell carcinoma. See Table 37-1.
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