Diagnostic Considerations
The clinical differential diagnosis of seborrheic keratoses includes malignant melanoma, melanocytic nevus, verruca vulgaris, condyloma acuminatum, fibroepithelial polyp, epidermal nevus, actinic keratoses, pigmented basal cell carcinomas, and squamous cell carcinomas.
Melanoma can clinically resemble seborrheic keratosis. A retrospective review of 9204 consecutive pathology reports from the Massachusetts General Hospital containing a clinical diagnosis of seborrheic keratosis revealed that 61 of these specimens (0.66%) were malignant melanoma. The submitted clinical differential diagnosis was seborrheic keratosis versus melanoma (31 cases, 51%), melanocytic nevus (17 cases, 28%), basal cell carcinoma (7 cases, 12%), squamous proliferation (3 cases, 5%), and no other differential diagnosis (3 cases, 5%).
Distinguishing superficial seborrheic keratoses from lentigo maligna and pigmented actinic keratoses may be difficult. The pigmented domed variety of acanthotic seborrheic keratoses may closely resemble a melanocytic nevus, but the surface is less lustrous and the follicular orifices are plugged.
Some seborrheic keratoses have a verrucous architecture that can produce a clinical and histologic appearance similar to an aging viral wart. Routine histopathologic examination may not reliably make this distinction, and special studies to look for evidence of papillomavirus DNA may be needed.
An inflamed seborrheic keratosis may be confused with a malignant melanoma or a squamous cell carcinoma.
Pigmented basal cell carcinomas usually are rather irregular with a rolled edge, a thin shiny epidermis with telangiectases, and a depressed or ulcerated center.
Inflammatory eruptions (eg, psoriasis, [24] pemphigus erythematosus [25] ) have been confused with seborrheic keratoses.
The use of topical products to achieve a "sunless tan" is increasing. Approximately 15% of women aged 18-24 years use sunless tanners. These topical products contain the active ingredient dihydroxyacetone (DHA). The artificial tan can alter the appearance of a skin lesion. More than one patient has been referred to a skin cancer clinic with a history of a change in the appearance of a pigmented lesion from which the use of sunless tanners was revealed after inquiry. [26]
Differential Diagnoses
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Sharply circumscribed elevated seborrheic keratoses.
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Closer view of multiple seborrheic keratoses in an autosomally dominant mode of inheritance.
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Seborrheic keratoses projecting above the level of the epidermis. Cysts represent sections of hyperkeratotic follicles.
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Seborrheic keratosis showing lackluster surface and appearance of being stuck on the skin surface.
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This is an autosomal dominant form of multiple seborrheic keratoses. This man's daughter is developing a similar distribution and quantity of seborrheic keratoses.
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The back of this same patient as in the image above with multiple seborrheic keratoses. His face had a similar number of seborrheic keratoses.
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Acanthotic type of seborrheic keratosis.
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Higher-power view of the cells in an acanthotic seborrheic keratosis.
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Hyperkeratotic type of seborrheic keratosis.
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Reticulated (or adenoid) type of seborrheic keratosis.
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This is a reticulated (or adenoid) seborrheic keratosis with abundant pigment.
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Seborrheic keratosis with inflammation in the dermis.
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This seborrheic keratosis was a pedunculated lesion in an axillary fold. Clinically, it had some resemblance to a skin tag.
