Review Question - QID 102785

This patient has psoriasis and is describing the Koebner phenomenon- a psoriatic eruption at the site of recent skin trauma. Diagnosis can be made clinically and, in rare cases, biopsy can be used as a confirmatory tool.

Psoriasis is a chronic autoimmune skin condition that often manifests with additional systemic symptoms. Plaque psoriasis is the most common phenotype and presents with silvery skin lesions on an erythematous base, generally on the extensor surfaces of joints. Other findings may include: fingernail pitting, psoriatic arthritis, and Auspitz sign (pinpoint bleeding after removal of underlying skin).

Weigle et al. discuss epidemiology and diagnosis of psoriasis. Psoriasis affects approximately two percent of the population in the United States. It is commonly diagnosed between ages 15-30 years has a clinical course that is unpredictable. Those with psoriasis have an increased risk of lymphoma, cardiovascular disease, and depression. Plaque psoriasis is most common and is defined as well demarcated scaly plaques that are pruritic and sometimes painful.

Raychaudhuri et al. review the various clinical phenotypes of psoriasis. There are currently no diagnostic criteria for psoriasis; diagnosis is clinical and can be confirmed with biopsy. Beyond plaque psoriasis, other forms include: inverse psoriasis, erythrodermic psoriasis, guttate psoriasis, and pustular psoriasis. Biopsy of a psoriatic lesion reveals parakeratosis in the stratum corneum, lack of stratum granulosum, and elongated rete ridges.

Figure A demonstrates a circular, well demarcated scaly lesion superimposed on a mild abrasion. Figure B demonstrates nail pitting, a common manifestation in patients with psoriasis. Illustration A demonstrates lichen planus occurring after skin trauma.

Incorrect Answers:
Answer 1: Hypertrophic scars occur within the site of skin injury and manifest as deposits of excess collagen.
Answer 2: An abrasion is an area of scraped skin. It does not exhibit scaly, pearly plaques as does psoriasis.
Answer 4: Lichen planus presents as violaceous, flat-topped papules with a lace-like lines (Wickham's striae). It can also be associated with Koebner's phenomenon (Illustration A).
Answer 5: Seborrheic dermatitis presents as erythematous, flaky lesions that usually appear on the face or scalp in adults.