Itchy skin lesions

A 47-year-old woman is seen in the dermatology clinic with a 5-month history of itchy eruption consisting of lesions mainly on her feet but also scattered on her legs. The rest of her skin is unaffected. She does not complain of any symptoms in her mouth or involving the genital area. On direct questioning she had noticed that some of her nails have become slightly brittle and are liable to splitting. No one else in the family is currently affected, although she thinks her mother had suffered with a similar skin eruption some years previously. She is otherwise well and not taking any regular medication. 

Examination 

There are multiple, discrete, purplish, shiny flat-topped papules over the dorsum of her feet; some of the lesions have a lacy white pattern over their surface. Further similar lesions are seen scattered on her lower legs; some of the papules are clustered in a linear fashion demonstrating Koebner’s phenomenon. A number of her fingernails have longitudinal ridges on them with ‘V-shaped’ nicks. Her mouth, genital region and scalp are all normal.