Lichen Planus (LP)
Prevalence of 0.5%. F>M, but males usually affected earlier.
Cause unknown – viewed as autoimmune (t-cell mediated attack at epidermal-dermal cell junction) or a hypersensitivity reaction. Commonly associated with other autoimmune disorders (eg ulcerative colitis, diabetes mellitus)
Characterised by multiple severely pruritic flat topped violaceous or purple shiny papules with fine white lines (Wickham’s striae) and scales; 1-5mm; distributed over flexor surfaces, wrist, forearm, leg, ankles, oral mucosa, genitalia, nails and scalp. Can affect just palms and soles.
Five P’s are characteristic of skin lesions – Plentiful, Pruritic, Polygonal, Polished, Purple, Papular, Planar
Nails – affected in 10-15% - thinning, longitudinal ridging, distal splitting
Mostly runs a course of 6 – 12 months and resolves
generalised – widespread, affecting most parts of body
follicular (lichen planopilaris) – small keratotic lesions involving scalp
localised – may become thickened and hypertrophic at any site
palm and sole – difficult diagnostic challenge (especially if other sites not affected); can resemble palmopustular psoriasis or one of the hereditary keratodermas; lesions tend to be sheet like rather than discrete – often hyperkeratotic and yellowish.
10% have nail dystrophy (“20-nail dystrophy”) – also get ridging, irregular pitting, splitting, loss of nail, pterygium formation