Lichen Planus Pigmentosus — SCE Dermatology MCQ

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HardInflammatory DermatosesLichen Planus PigmentosusSCE Dermatology

A 50-year-old woman has widespread lichen planus pigmentosus. She has diffuse brown-grey hyperpigmentation on her face and neck in a reticular pattern. What is the cause of the characteristic colour?

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Correct answer: E — Dermal melanin (melanin incontinence from basal layer damage dropping pigment into the papillary dermis — dermal melanophages give the grey-brown colour)

Lichen planus pigmentosus (LPP) shows grey-brown pigmentation because melanin from damaged basal layer keratinocytes drops into the papillary dermis (melanin incontinence) where it is phagocytosed by dermal melanophages. The dermal melanin gives the characteristic grey-blue hue (Tyndall effect — deeper melanin appears grey/blue). This is the same mechanism producing post-inflammatory hyperpigmentation in LP and other interface dermatitides. LPP is more common in darker skin types and is associated with frontal fibrosing alopecia. Treatment is challenging — sun protection, topical hydroquinone, topical tacrolimus, and azelaic acid may help but response is often slow and incomplete. The dermal pigment is particularly resistant to treatment.

Reference: BAD 2019 LP; Skin of Colour