Pityriasis rubra pilaris or follicular psoriasis?

Abstract

In this case we carried out a biopsy because the clinical lesions indicative of chronic-recurrent follicular psoriasis arose at the age of 5 months and were located mainly on the abdomen; other doubts about the diagnosis of psoriasis were due to the negative family history and the lack of involvement of the conventional areas. Histology did not favor the diagnosis of psoriasis: there was not an obvious parakeratosis, there was not thinning of the skin at the top of the dermal papillae, there were not widened epidermal ridges and isolated or grouped in microabscesses neutrophils lacked. The histology was more reminiscent of pityriasis rubra pilaris due to the lack of psoriatic findings, the presence of some areas of orthokeratosis and follicular keratinous plugs. This case confirms the difficulties of differential diagnosis between psoriasis and pityriasis rubra pilaris (1, 2).