Clinical lichenification is the condition of hyperkeratotic exaggerated skin markings.  Contact dermatitis, atopic dermatitis, and many other dermatitides which generate a cycle of chronic itching and chronic scratching and rubbing of a neurodermatitis-like nature can lead to the following histological changes of lichenification:

Epidermal hyperplasia (expressed in acanthosis, hypergranulosis, and parakeratotic or orthokeratotic hyperkeratosis), fibrosis of superficial dermis (including “wiry collagen”), with vertical collagen bundles, and thickening of the walls of small vessels.  Any inflammatory infiltrate is usually minor and may be absent¹. Dermal stellate fibroblast nuclei attest to chronic rubbing or manipulation of skin².

In contrast to psoriasis, the suprapapillary epidermis is not especially (though may seem so in any papillomatous areas) thin.  Recent exacerbation/activity may express itself with focal areas of hypo-granulosis, parakeratosis and edema.

This is also otherwise a sort of “dry” eczematous reaction to be contrasted with a more acute and ordinary definition of the histology of eczema as a reaction rich in superficial dermal edema and epidermal spongiosis¹. 

Psoriasiform tissue reactions, on the other hand, consist of epidermal hyperplasia plus some suprapapillary exudate and focal related parakeratosis². As below, lichenification can get superimposed on psoriasiform.

Lichenification is typified clinically by accentuation of normal skin markings, hyperpigmentation, and induration of variable extent, the classic constellation of the surface reaction, especially in the scalp, genitalia can be so extensive that at first glance the epidermis resembles that of normal palm or sole.  Lichenification can be produced in a neurodermatitic fashion or superimposed on a variety of chronic itchy disorders such as allergic contact dermatitis, atopic dermatitis, nummular dermatitis or even on a neoplastic process such as mycosis fungoides or leukemia cutis.  Dr. Ackerman has noted that the finding of “wiry collagen” can be a tip off to MF.  But, it may be seen in other instances such as a chronic eczematous lesion of the breast nipple (S09-14044) or allergic contact dermatitis or atopic contact dermatitis (S09-9799). 

References:

1. Pinkus H, 2nd edition, 1976, A guide to dermatohistopathology.
2. Ackerman AB, 3rd edition, 2005, “Histologic diagnosis of inflammatory skin diseases, an algorithmic method based on pattern analysis”.

(posted 11/29/09)