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Lichen Planus — SCE Dermatology MCQ

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EasyInflammatory DermatosesLichen PlanusSCE Dermatology

A 50-year-old man has lichen planus. His dermatologist explains that LP is characterised by the 6 Ps. What are the 6 Ps?

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Correct answer: A — Purple, Polygonal, Planar, Pruritic, Papules, Plaques

The 6 Ps of lichen planus are a classic mnemonic: Purple (violaceous colour), Polygonal (angular/geometric outline), Planar (flat-topped), Pruritic (intensely itchy), Papules, and Plaques. These describe the characteristic morphology of cutaneous LP affecting the flexor wrists, shins, lower back, and ankles. The distribution and morphology help distinguish LP from psoriasis (silvery scale, extensor surfaces), drug eruption (more widespread, less polygonal), and secondary syphilis (painless, palmoplantar involvement). Wickham striae (fine white lines on the surface of LP papules) are an additional diagnostic feature seen with dermoscopy or magnification.

Reference: BAD 2019 LP Guidelines