[How I explore ... a lichenoid drug reaction]

Lichenoid drug reactions are specific unwanted cutaneous side-effects related to some drugs. The clinical presentation of the lesions often suggests the diagnosis, but the distinction with idiopathic lichen planus remains difficult. The diagnosis is firmly established by the dermatopathological assessment of a cutaneous biopsy. The anamnestic search is focused on drug imputability based on well defined criteria. Biologic evaluations and various in vitro tests are little contributive and even may prove to be irrelevant.