A Case of Naevoid Blaschkoid Psoriasis in a Two-Year-Old Child.

Psoriasis is a chronic, immune-mediated skin disorder characterised by well-demarcated erythematous plaque with micaceous scale. Naevoid Blaschkoid psoriasis is an unusual subtype that occurs along Blaschko lines. A two-year-old boy presented with erythematous scaly lesions distributed along the lines of Blaschko over the bilateral upper limb, the front of the chest, back, and the right lower limb. The lesions appeared four months ago and slowly progressed. There was no history of trauma, no skin lesions in other parts of the body, and no significant family history. Nail and mucosa were normal. Histopathology showed psoriasiform dermatitis with characteristics of psoriasis. The child was treated with topical clobetasol propionate 0.05% cream. Naevoid Blaschkoid psoriasis, in the absence of psoriatic lesion elsewhere on the body, is a rare manifestation. It has striking similarity with inflammatory linear verrucous epidermal nevus (ILVEN), both clinically and histologically. Naevoid psoriasis usually presents late, is asymptomatic or mildly pruritic, progresses rapidly, and responds favourably to antipsoriatic treatment. In contrast, ILVEN presents early, is intensely pruritic, slowly progressive, and is usually refractory to antipsoriatic treatment. Histologically, ILVEN demonstrates abruptly alternating areas of hypergranulosis with orthokeratosis, and parakeratosis with agranulosis. An inflammatory infiltrate is present in the upper dermis. Psoriasis presents with papillomatosis, acanthosis, and parakeratosis with absent or minimal granular layer. Immunohistochemical staining can be done in such doubtful cases. Involucrin would be detectable in psoriasis, but it is absent in ILVEN. Pathogenesis of linear psoriasis is unknown but might be explained by the concept of genetic mosaicism. Although rare, there have been a few reported cases of linear psoriasis occurring in early childhood.