LICHENOID REACTION
The lichenoid reaction is characterized by keratinocyte enlargement associated with Civatte body (colloid body) production. A superficial lymphocytic infiltrate that disrupts the dermoepidermal junction is present in the active phase of the lichenoid reaction. Hypergranulosis, hyperkeratosis, and 'saw tooth' acanthosis are variably present. This reaction is seen in a variety of clinical settings. Lichen planus is the prototype for which the reaction is named. The same reaction is seen in solitary lesions of more than 4 months duration (lichenoid keratosis), in lichenoid drug reactions, in some cases of graft versus host reaction, in some inflamed seborrheic keratoses, in some cases of lupus erythematosus, in lichen striatus, in active lesions of erythema dyschromicum perstans, in some lesions of mycosis fungoides, in the central part of some lesions of porokeratosis, in secondary lues, in some actinic keratoses, and as a component in other lesions.
Chronic scratching or rubbing may result in epidermal hyperplasia and fibrosis of the papillary dermis, particularly in lichen planus of the legs. This is characteristic of hypertrophic lichen planus. The basic pathology of lichen planus may be masked by these changes, and the pathology mistaken for lichen simplex chronicus.

 
Low power view showing transepidermal keratinocyte enlargement in the left side of the picture compared to keratinocytes of more normal size in the right side of the picture. A superficial lymphocytic infiltrate is also seen.
High power view of above. Arrows point to some of the Civatte bodies (colloid bodies).

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