Scraping of this scale may result in pinpoint bleeding. This is known as the Auspitz sign. New rash patches often break out at sites of trauma to the skin. This is a valuable sign for diagnosis, called the Koebner phenomenon. The scalp, knees, elbows, umbilicus, buttocks creases, and genitals are the most common areas of rash.
Nail involvement is common and valuable for making the diagnosis.
While psoriasis is rare in newborns, it can be a great mimic and resist diagnosis at first. When the first outbreak is in the diaper area, it can mimic seborrheic dermatitis, eczematous diaper dermatitis, perianal streptococcal disease, or yeast infection. Guttate psoriasis is a variant that occurs predominantly in children. It is marked by a dramatic eruption of many small, oval or round lesions that morphologically are identical to the larger plaques of psoriasis over the trunk, face, and upper limbs. This eruption often occurs after a streptococcal infection.