A 65-year-old man comes to the office due to skin lesions on his back. He first noted the spots 5 years ago and says they are becoming more numerous. The lesions are occasionally pruritic but are otherwise asymptomatic. The patient did not come for evaluation previously because he "did not care about them," but made an appointment now at his wife's insistence. Medical history is notable for hypertension, hyperlipidemia, and type 2 diabetes mellitus. On examination, there are numerous pigmented plaques, as shown in the image below. Which of the following is the most likely diagnosis?

Question

A 65-year-old man comes to the office due to skin lesions on his back.  He first noted the spots 5 years ago and says they are becoming more numerous.  The lesions are occasionally pruritic but are otherwise asymptomatic.  The patient did not come for evaluation previously because he "did not care about them," but made an appointment now at his wife's insistence.  Medical history is notable for hypertension, hyperlipidemia, and type 2 diabetes mellitus.  On examination, there are numerous pigmented plaques, as shown in the image below.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

Seborrheic keratosis (SK) (plural: keratoses) is a common, tan or brown, epidermal tumor occurring in middle-aged or elderly individuals. It has a variable appearance from nearly flat macules to raised, wart-like lesions, ranging in size from a few millimeters to centimeters. SK typically has a velvety or greasy surface and well-demarcated border, and is often described as having a "stuck-on" appearance. On microscopic examination, the lesions of SK are composed of small cells resembling basal cells, with variable pigmentation, hyperkeratosis (thickening of the stratum corneum), and keratin-containing cysts. The etiology of SK is not fully understood; however, it is frequently associated with activating mutations of the fibroblast growth factor receptor 3. SK itself is benign, but rapid onset of numerous SKs (Leser-Trélat sign) is often associated with an internal malignancy (eg, gastric adenocarcinoma), possibly due to overproduction of insulin-like growth factor 1 and other cytokines. (Choice A) Acanthosis nigricans is characterized by hyperpigmented, velvety plaques at flexural areas (eg, axilla, posterior neck). It is associated with diabetes mellitus, obesity, visceral malignancy, and various endocrinopathies. (Choice B) Actinic keratosis presents with hyperkeratotic lesions in sun-exposed areas of the scalp, ears, face, and hands. These lesions are unpigmented and, despite the similar name, are unrelated to seborrheic keratosis. (Choice C) Lichen planus is characterized by the "5 Ps": polygonal, planar, pruritic, purplish plaques on the wrists, hands, trunk, and legs. Fine white lines (Wickham striae) may be present on the plaque surface. (Choice D) Melanoma characteristically presents as an asymmetric, pigmented lesion with an irregular border, variable coloration, and change in size and appearance over time. Multifocal development of monotonous, otherwise asymptomatic lesions is much more typical of SK. (Choice E) Psoriasis presents with scaly, nonpigmented plaques. Although it may occur on the trunk, it is more common on the extensor surfaces of the extremities. Educational objective: Seborrheic keratosis is a common epidermal tumor that presents as a tan or brown, round lesion with a well-demarcated border and "stuck-on" appearance. Microscopic examination shows small cells resembling basal cells, with pigmentation, hyperkeratosis, and keratin-containing cysts. Rapid onset of numerous lesions is often associated with internal malignancy (Leser-Trélat sign).

A 65-Year-Old Man Comes to the Office Due to Skin