A well-demarcated, rough, leathery rash on the right side of

A 23-year-old female comes to clinic complaining of a rash on the right side of her neck. She states that the rash constantly itches. On exam, there is a well-demarcated, rough, leathery rash on the right side of her neck with small, red papules. There are numerous scratch marks. What is the most likely diagnosis?

A. Lichen simplex chronicus

B. Lichen planus

C. Lichen sclerosus

D. Pityriasis rosea

E. Erysipelas

Choice (A) is the answer.

Lichen simplex chronicus, also known as neurodermatitis, results in lichenification of the skin secondary to constant itching and scratching. Commonly affected areas include the neck, wrists, ankles, forearms, and genitals. Repetitive itching and scratching results in a well-demarcated, rough, leathery area of skin with deep skin creases. There may be thick, scaly plaques and small red papules. Histologically, lichen simplex chronicus is characterized by hyperkeratosis, acanthosis and elongation of rete pegs. The dermal papillae are broad and elongated, and there are inflammatory cells in the fibrosed dermis.

Lichen planus (Choice B) is an inflammatory mucocutaneous condition that is characterized by pruritic, flat-topped, polygonal plaques and papules. Lesions have a white, lace-like, reticular pattern known as Wickham's striae. Lichen planus can be remembered by the 6 P's: pruritic, purple, polygonal, planar, papules, and plaques. Histologically, lichen planus is characterized by hyperkeratosis with irregular thickening of the epidermis that gives a saw-tooth-like appearance. There is a lymphocytic infiltrate at the dermal-epidermal border and apoptotic keratinocytes known as Civatte or colloid bodies can be seen in the basal layer. Lesions often affect the wrists and ankles, and there may be oral mucosal involvement. Lichen planus is associated with hepatitis C and a number of medications.

Lichen sclerosus (Choice C) is a chronic skin condition that typically affects the genitals and perianal area and occurs most often in post-menopausal women. Symptoms include vaginal itching, soreness, and pain during sexual intercourse. Lichen sclerosus is associated with characteristic white, shiny, smooth patches on the vulva. The labia become thin and atrophied resulting in bleeding and bruising. Scarring can lead to narrowing of the vagina and pain during sexual intercourse. Lichen sclerosus increases the risk of vulvar carcinoma, in particular squamous cell carcinoma. Histologically, lichen sclerosus is characterized by dermal and epidermal atrophy with loss of rete pegs. There is hyperkeratosis and dense fibrosis of the papillary dermis with perivascular inflammatory cells. Lichen sclerosus is treated with corticosteroids.

Pityriasis rosea (Choice D) is a benign rash that begins with an initial herald patch which is a 1-2 cm salmon-colored plaque with a darker, scaling periphery. The rash progresses to small, pink, oval to round scaling plaques and papules that look like small herald patches. The secondary rash is located along the lines of skin cleavage and appears in a Christmas tree distribution. Pityriasis rosea is self-limiting.

Erysipelas (Choice E) is a superficial skin infection with lymphatic involvement that is caused most often by group A beta-hemolytic streptococci. Group A beta-hemolytic streptococcus, known as Streptococcus pyogenes, is a gram positive, catalase negative cocci that is sensitive to bacitracin. Erysipelas may present initially with constitutional symptoms followed by the development of a painful, erythematous, raised, well-demarcated rash. The classic facial rash has a characteristic butterfly distribution with the bridge of the nose affected. Erysipelas is not, however, limited to the face. Children and the elderly are most commonly affected.