Porokeratosis ptychotropica on the buttocks

A 63-year-old man presented with a 20-year history of itchy, reddish-brown, well-demarcated, bilateral and symmetrical hyperkeratotic plaques on the buttocks, along with peripheral discrete papules [Figure 1a]. There was no similar family history. He was a known diabetic for five years and denied the use of immunosuppressants. Dermoscopy showed well-circumscribed areas with central scar like structures, peripheral scaling, irregular punctate and globular vessels along with brown pigment granules on a reddish brown background [Figure 1b]. Skin biopsy showed parakeratotic columns intercalating epidermis in some areas, in which dyskeratotic cells could be seen, and a lymphocytic infiltrate in the upper dermis, confirming the diagnosis of porokeratosis ptychotropica. The cause of this, may be due to the frequent mechanical friction by long term farming. Porokeratosis ptychotropica is a rare variant of porokeratosis initially described in 1995. It is clinically characterized by a keratotic ridge with a central groove and histologically by cornoid lamella which is the key to differentiate it from neurodermatitis, chronic eczema, psoriasis and epidermal nevus. Though effective therapeutic strategies are lacking, early diagnosis of this condition is important as there is 7.5% to 11% risk of malignant transformation.

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Figure 1a:

Well-demarcated, reddish- brown, bilateral and symmetrical plaques with hyperkeratotic surface on the buttocks along with peripheral discrete papules

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Figure 1b:

Well-circumscribed areas with central scar-like structures, peripheral scaling, irregular punctate and globular vessels along with brown pigment granules on a reddish brown background

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