Histological Reaction Patterns

A. Superficial perivascular dermatitis: Nearly all the common inflammatory diseases of the skin (eczema, psoriasis, lichen planus) affect the vessels of the superficial vascular platex, which is situated in the upper reticular dermis.

1. Eczematous tissue reaction (spongiotic dermatitis) The prototype of this reaction pattern is the sequence of events that follow applications of irritants or contact allergens to the skin surface. The changes are characteristically epidermal and include intercellular edema, acanthosis, spongiosis, and parakeratosis, all in focal distribution. In subacute or acute eczema, these changes extend and lead to intraepidermal vesicles, which sometimes contain cells. The dermal changes are entirely secondary to the epidermal changes and consist of edema of the papillary dermis and a lymphohistiocytic infiltrate around the venules of the superficial papillary plexus.

2. Psoriasiform tissue reactions the principal teatures of psoriasiform reaction are suprapapillary exudates and focal parakeratosis. The suprapapillary exudates stimulates epidermal mitosis. In chronic psoriasis, this leads to prominent psoriasiform hyperplasia. Psoriasiform tissue reaction occur in psoriasis, seborrheic dermatitis, perioral dermatitis, nummular eczema, and Reiter’s diseases. In psoriasis, there is early acanthosis which later becomes psoriasis. The suprapapillary areas become thinned, and the surface is covered by a lamellated scale with alternating layers of orthokeratotic and parakeratotic stratum corneum. Accumulation of pyknotic polymorphonuclear leukocytes are typically also found in the horny layer (Munro microabscesses).

3. Interface dermatitis – can be subdivided according to whether vacuolar alteration or a cellular infiltrate.

a. Vacuolar type – there is little inflammatory infiltrate present. The major entity of this type is erythema multiforme, in which there is vacuolar alteration of the basal layer of the epidermis. Associated with formation of necrotic keratinocytes and confluent epidermal necrosis.

b. Lichenoid type there is dense bandlike infiltrate in the papillary dermis that tends to “hug” the rete ridges. The major entity of this type is lichen planus, in which the changes of liquefactive degeneration of the basal epidermal layer excite a vigorous lymphohistiocytic inflammatory response. Pink-staining homogeneous globs called colloid bodies occur focally or in clumps. There are degeneration dead keratinocytes. The granular layer becomes irregularly thickened, and there is uniform hyperkeratosis.

Дата добавления: 2015-08-03