Fig. 5.1
Biopsy from a solitary plaque of LSC reveals compact orthohyperkeratosis, marked epidermal hyperplasia, and fibrosis of the superficial dermis along with a mild lymphocytic infiltrate
What Is Psoriasiform Dermatitis?
Psoriasiform dermatitis is a histological term that refers to a group of disorders that histologically mimic psoriasis. Chief among them in frequency are lichenified dermatitis or lichen simplex chronicus (LSC) , seborrheic dermatitis , and pityriasis rubra pilaris (PRP) . Secondary syphilis and mycosis fungoides (MF) may both reveal findings of psoriasiform dermatitis among their many histological presentations.
So What Are Those Findings?
For a biopsy specimen to be interpreted as psoriasiform dermatitis it must have the following findings, which are usually characteristic of plaque psoriasis, albeit to a lesser degree (otherwise they would represent psoriasis):
Epidermal hyperplasia that tends toward regular and favors the rete
Parakeratosis
No or at the best, mild spongiosis
Other findings may include neutrophils in the horny layer, exocytosis, and a superficial infiltrate.
It is primarily the regular epidermal hyperplasia that pathologists require for labeling a dermatitis psoriasiform . Some use the term psoriasiform as an adjective for the epidermal hyperplasia rather than for the dermatitis, speaking of psoriasiform epidermal hyperplasia to mean regular epidermal hyperplasia like in plaque psoriasis.
Clinical Disorders with Histological Findings of Psoriasiform Dermatitis
Disorders in this group include
