Histologic features in lichenoid drug eruption and lichen planus

Differential criteria	Lichen planus	Lichenoid drug eruption
Cornified layer	Compact hyperorthokeratosis, seldom a moderate degree of parakeratosis	Focal parakeratosis; cytoid bodies in the cornified layer
Epidermis	Thickened stratum granulosum at acrosyringia and acrotrichia, irregular saw-tooth-like acanthosis, necrotic keratinocytes in the lower epidermal layers	Thickened stratum granulosum possible, however, with focal interruption of the granular layer, cytoid bodies in the granular layer, necrotic keratinocytes scattered in all epidermal layers
Dermis	Mostly a superficial dermal inflammatory infiltrate; seldom eosinophils	More often a deep dermal inflammatory infiltrate (especially in non-photodistributed lichenoid drug eruption); admixture of eosinophils and plasma cells possible*

* Presence of plasma cell is a regular finding in biopsies from mucous membranes independently of the origin of dermatosis.

Graphic 83936 Version 1.0