Lichen planus is not a common skin disease but it does have
a very characteristic purple colour which helps in making the diagnosis. The
itchy purple polygonal papules can be seen individually on the volar wrist or
joined up as plaques like this on the shins. Here chronic rubbing can make them
thicken into purplish nodules which can be mistaken for squamous cell
carcinomas both clinically and surprisingly histologically because of the
pseudoepitheliomatous thickening of the epidermis. Usually small white lines
called Wickham’s striae can be seen on the plaque surface in lichen planus and
lesions may show some hyperpigmentation when partially healing but it is that
purple colour which is so distinctive. Always check the buccal surface of the
cheek for the typical white net like pattern of mucosal thickening seen in some
cases particularly due to drugs such as thiazide diuretics. Many cases though
are idiopathic possibly autoimmune but respond to strong topical steroids or
intralesional steroids for nodules on the shins.
