Page 869 - Robbins Basic Pathology by Vinay Kumar, Abul K. Abbas, Jon C. Aster

Chronic Inflammatory Dermatoses 855

AB

Figure 23–3 Psoriasis. A, Chronic plaques of psoriasis show silvery-white scale on the surface of erythematous plaques. B, Microscopic examination
reveals marked epidermal hyperplasia, uniform downward extension of rete ridges (psoriasiform hyperplasia), and prominent parakeratotic scale that
is focally infiltrated by neutrophils.

it can be widespread and severe. The clinical subtypes are A
defined by pattern of involvement and severity. Treatment
is aimed at preventing the release or actions of inflamma-
tory mediators. Depending upon the disease severity,
NSAIDS, immunosuppressive agents such as cyclosporin,
and TNF antagonists are used. Newer agents that inhibit
TH1 and TH17 immune responses are also being tested.

Lichen Planus

“Pruritic, purple, polygonal, planar papules, and plaques”
are the tongue-twisting Ps that describe this disorder of
skin and squamous mucosa. The lesions may result from a
CD8+ T cell–mediated cytotoxic immune response against
antigens in the basal cell layer and the dermoepidermal
junction that are produced by unknown mechanisms,
perhaps as a consequence of a viral infection or drug
exposure.

MORPHOLOGY B

Cutaneous lesions of lichen planus consist of pruritic, vio- Figure 23–4 Lichen planus. A, This flat-topped pink-purple polygonal
laceous, flat-topped papules, which may coalesce focally papule has white lacelike markings referred to as Wickham striae.
to form plaques (Fig. 23–4, A). These papules are often high- B, Microscopic features include a bandlike infiltrate of lymphocytes along
lighted by white dots or lines called Wickham striae. the dermoepidermal junction, hyperkeratosis, hypergranulosis, and
Hyperpigmentation may result from melanin loss into the pointed rete ridges (“sawtoothing”), which results from chronic injury of
dermis from damaged keratinocytes. Microscopically, lichen the basal cell layer.
planus is a prototypical interface dermatitis, so called
because the lesions are concentrated at the interface of the
squamous epithelium and papillary dermis. There is a dense,
continuous infiltrate of lymphocytes along the dermoepider-
mal junction (Fig. 23–4, B). The lymphocytes are intimately
associated with basal keratinocytes, which often atrophy or
become necrotic. Perhaps as a response to damage, the
basal cells take on the appearance of the more mature cells
of the stratum spinosum (squamatization). This pattern of
inflammation causes the dermoepidermal interface to assume
an angulated, zigzag contour (“sawtoothing”). Anucleate,
necrotic basal cells are seen in the inflamed papillary dermis
and are referred to as colloid bodies or Civatte bodies.