Pityriasis lichenoides in a 9-month-old boy.

Pityriasis lichenoides (PL) is a skin disease of unknown origin that is characterized by scaling papules. It is relatively common in childhood but very rare in the first year of life, with just 9 cases described in the literature. We report the case of a 9-month-old boy with no personal or family history of interest who was seen in our department for generalized skin lesions that had been present for a week. The patient was afebrile and had no other symptoms or known history of prior infection. Physical examination revealed papular scaling, erythematous-brownish lenticular lesions on the trunk and proximal extremities (Fig. 1). There was no mucosal involvement and the physical examination was otherwise normal. Histology showed a deep, perivascular lymphohistiocytic inflammatory infiltrate, with fibrinoid necrosis in the vessel walls and involvement of the dermal-epidermal junction. In the epidermis there was diffuse parakeratosis, focal exocytosis, isolated necrotic keratinocytes, and small foci of necrosis (Fig. 2). Immunohistochemical staining with anti-S100 protein and CD1 antibodies was negative. Based on the clinical and histologic findings, we diagnosed PL and prescribed topical corticosteroid therapy (methylprednisolone aceponate), which resulted in slight improvement of the lesions. The condition improved spontaneously over the following months, leaving residual postinflammatory hypopigmented macules.