Atopic Dermatitis and Psoriasis Overlap Syndrome: New entity or under-recognize variant?

Psoriasis (PsO) and atopic dermatitis (AD) have distinct features. However, lesions with both AD and PsO characteristics, or typical dermatitis patches present along with typical psoriasis plaques have been described and labelled as psoriasis dermatitis or PsEma, or psoriasiform dermatitis. Diseases grouped as psoriasiform dermatoses include lichen simplex chronicus, prurigo nodularis, pityriasis rubra pilaris, secondary syphilis and Reiter syndrome. How are these diseases related?
The immunopathogenesis and phenotypes of PsO with AD features, AD with PsO features, coexisting AD and PsO, development of AD-like dermatitis during PsO or AD treatment and development of PSO during AD treatment will be discussed.