These HLA types are not associated with the pustular form of the disease. The lesions consist of erythematous papules that coalesce to form plaques with sharply demarcated, irregular borders. The Koebner, or isomorphic, response, in which new lesions appear at sites of trauma, is a valuable diagnostic feature. Scalp lesions may be confused with seborrheic dermatitis, atopic dermatitis, or tinea capitis. Small raindrop-like lesions on the face are moderately common.
Age is an important factor in determining the clinical pattern.
Psoriasis is rare in neonates but may be severe and recalcitrant and pose a diagnostic problem. The initial lesions may involve the diaper area and mimic seborrheic dermatitis, eczematous diaper dermatitis, perianal streptococcal disease, or candidosis. Biopsy or prolonged observation may be required for definitive diagnosis. Other rare forms include psoriatic erythroderma, localized or generalized pustular psoriasis, and linear psoriasis. Hospitalization may be required for severe forms of the disease.