Psoriasis is usually associated with plaque formation. Some people (mostly children and young adults), however, explosively develop 50 to 100 small, nonconfluent papules over the trunk and proximal extremities. This phenomenon, known as guttate psoriasis, is particularly likely to be precipitated by a preceding streptococcal infection or by an episode of severe emotional stress. The Koebner phenomenon and nail pitting are often absent.The eruption of rubella (German measles) occurs after several days of upper respiratory symptoms. It consists of light led macules or very slightly elevated papules that
first appear on the face and neck but quickly spread to the trunk and extremities. Cervical, postauricular, and suboccipital lymphadenopathy is usually present. Strictly speaking, the lesions of rubella are not scaling, but at the time the patient is first examined, postinflammatory desquamation has usually started resulting in the appearance of a fine, pityriasis-like scale over the earliest lesions. Facial lesions often become confluent, but those elsewhere usually remain discrete.
The eruption rubeola (measles) occurs in association with marked fever, coryza, conjunctivitis, and cough. It consists of macules and barely palpable papules that first appear on the forehead and behind the ears. Lesions rapidly spread to the face, trunk, and limbs. Koplik spots (white dots with surrounding red rings) are usually present on the buccal surfaces opposite the molars. Here, too, postinflammatory desquamation leads to a minor amount of scale formation. Coalescence of lesions occurs on the face, but limb lesions remain discrete.