A 25-year-old woman comes to the office due to a 4-week history of a pruritic skin rash. The patient has no chronic medical conditions and takes no medication. Vital signs are normal. On examination, there are pink papules distributed symmetrically over the anterior surfaces of the shins and ankles. Shave biopsy reveals prominent hyperkeratosis along with a thickened granular layer. In addition, there is a bandlike infiltrate of mononuclear cells (predominantly lymphocytes) in the subjacent superficial dermis that involves the overlying epidermis. The rete ridges have a sharpened, sawtooth appearance. The basal layer of the epidermis is degenerated, with scattered colloid bodies. Which of the following is the most likely diagnosis?

Question

A 25-year-old woman comes to the office due to a 4-week history of a pruritic skin rash.  The patient has no chronic medical conditions and takes no medication.  Vital signs are normal.  On examination, there are pink papules distributed symmetrically over the anterior surfaces of the shins and ankles.  Shave biopsy reveals prominent hyperkeratosis along with a thickened granular layer.  In addition, there is a bandlike infiltrate of mononuclear cells (predominantly lymphocytes) in the subjacent superficial dermis that involves the overlying epidermis.  The rete ridges have a sharpened, sawtooth appearance.  The basal layer of the epidermis is degenerated, with scattered colloid bodies.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec160b_38fc_68ee_9249_55b8e55fd529_MD0001_00 This patient has a pruritic rash consistent with lichen planus (LP), an immunologically mediated skin disorder primarily affecting middle-aged adults. The skin lesions typically occur symmetrically on the flexural surfaces of the wrists and ankles but can also involve the nails, oral mucous membranes, and genitalia. The characteristic skin lesions are described by the 5 Ps: pruritic, purple/pink, polygonal papules and plaques and can form along lines of minor trauma (Koebner phenomenon). Chronic lesions often show white, lacy markings known as Wickham striae. Although the etiology of LP is unknown, it is characterized by a (CD8+) T cell-mediated response to the cells along the junction of the dermis and epidermis, resulting in the following characteristic histologic findings: (Choices A and B) Atopic dermatitis can cause a pruritic rash affecting the extremities, but it usually presents in childhood and most patients have a history of other atopic disorders (eg, allergic rhinitis, asthma). The lesions in contact dermatitis are also pruritic but occur in localized areas corresponding to the specific exposure (eg, waist with nickel belt buckle exposure). Biopsy in these conditions would show spongiosis (epidermal edema) in the acute phase and acanthosis (diffuse epidermal hyperplasia) in chronic disease. (Choice C) Erythema nodosum is a delayed-type hypersensitivity reaction that presents with tender inflammatory nodules in the subcutaneous fat, primarily on the shins. The characteristic histopathologic finding is septal panniculitis in the subcutaneous tissues, with a variable (lymphocytes, neutrophils, macrophages) infiltrate. (Choice E) Psoriasis is an immune-mediated inflammatory disease characterized by cytokine-driven keratinocyte hyperproliferation leading to acanthosis with clubbed rete ridges, parakeratosis (retention of nuclei in stratum corneum), and thinned stratum granulosum. It also demonstrates the Koebner phenomenon but usually presents with chronic erythematous plaques with silvery scales on the extensor surfaces of the knees and elbows, scalp, or neck. Educational objective: Lichen planus presents with pruritic, purple/pink, polygonal papules and plaques that can affect the flexural surfaces of the wrists and ankles, along with the nails, oral mucous membranes, and genitalia. Histologic findings include hyperkeratosis (thickening of stratum corneum), lymphocytic infiltrates at the dermoepidermal junction, hypergranulosis (prominent granular layer), sawtooth rete ridges, and scattered eosinophilic colloid bodies.

A 25-Year-Old Woman Comes to the Office Due to a 4-Week