15 “P”s of Lichen Planus

In your medical school, you must have heard about the 5 “P”s of Lichen planus representing the gross morphology of Lichen Planus. This 15 P mnemonic encompasses morphology, drug and other associations and histology of lichen planus.

wickhams stria lichen planus
Wickham’s Stria
James, Candice, Mai [CC BY-SA 3.0], via Wikimedia Commons

Morphology:
Pruritic
Planar (Flat-topped)
Polygonal
Purple
Papules
Pattern of white lines on papules (Wickham’s stria)
Pterygium in nails
Phenomenon of Koebner (Prior trauma areas)
Phelxural surface (Flexural – forearm/wrist/ankle)

Histology:
Pink (Eosinophilic) civatte bodies in papillary dermis
Pointed rete Pegs (Saw-tooth rete ridges)

Causes:
Phlavivirus (Flavivirus – Hepatitis C virus association)
Pressure drugs (ACE inhibitors, Beta blockers, Thiazides)
Plasmodium killer (Chloroquine)
Penicillamine

Pigmentation after treatment

Sawtooth lichen planus
Sawtooth

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