Classical dermoscopy of porokeratosis

A 55-year-old male presented to the dermatology department with itchy blackish-raised lesions over the trunk and extremities for 2 months [Figure 1a]. On examination, the patient had multiple well-defined annular hyperpigmented plaques with peripherally raised thread-like hyperkeratotic borders over the back, trunk, and extremities [Figure 1b and c]. Dermoscopy (×26 magnification, polarized, both contact and non-contact using dino-lite edge) showed central brownish discoloration surrounded by white tracks with a prominent pigmented peripheral ridge [Figure 2a and b]. Based on clinical examination and dermoscopy, patient was diagnosed with porokeratosis. The patient was treated with a topical retinoid and the lesions resolved.

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Figure 1:

(a) Multiple annular hyperpigmented plaques present over the dorsum of the left hand and upper abdomen. (b) Well-defined annular hyperpigmented plaque with peripheral raised thread-like hyperkeratotic border present over the left clavicular area. (c) Well-defined annular hyperpigmented plaque with prominent border present over the abdomen (Closer view).

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Figure 2:

(a) Dermoscopy revealed central brownish discoloration surrounded by white tracks with a more prominent peripheral ridge (Non-contact, Polarized, ×26 magnification using dino-lite edge). (b) Dermoscopy revealed central brownish discoloration surrounded by white tracks with a more prominent pigmented peripheral ridge (Contact, Polarized ×26 magnification using dino-lite edge).

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Porokeratosis is a clonal keratinizing disorder with etiopathogenesis being doubtful and characteristic histopathology of cornoid lamella. Its response to treatment is also variable. It predominantly affects eccrine ostia with abnormality in the mevalonate kinase pathway, which is involved in cholesterol and steroid biosynthesis. It is known for its characteristic clinical manifestation of a prominent peripheral thread-like border, with histopathology showing cornoid lamella. Cornoid lamella is a tightly packed thin column of parakeratotic cells with a zone of focal hypogranulosis below it. Dermoscopy reveals central brownish discoloration with bluish-gray dots and a peripheral “white track.” After polyvinylpyrrolidone-iodine application, iodine absorption by the cornoid lamella makes the ridge and rim more prominent. Certain variants have malignant transformation.^[1]