Differentials
Malignant melanoma
SIGNS / SYMPTOMS
Malignant melanoma is the most important differential diagnosis of seborrheic keratosis. Sometimes differentiating between seborrheic keratosis and melanoma is a challenge. A key feature is that a melanoma tends to vary more in color, such as brown, blue, black, gray, and red, whereas a seborrheic keratosis usually is limited to shades of tan, brown and black.
Melanoma usually has a smooth surface that can vary in height, while seborrheic keratosis usually looks the same across the whole surface. Melanoma does not generally have the warty, "stuck-on" appearance of seborrheic keratosis.[1][31]
Melanoma is less uniform and less symmetrical in color and shape than seborrheic keratosis.
INVESTIGATIONS
Dermoscopy: dark pigmentations forming an asymmetric ring around follicular openings, slate-gray dots and areas of irregular, broadened network. Also, biopsy and histopathologic examination are used to differentiate.
Viral warts
SIGNS / SYMPTOMS
More commonly located on hands and feet.
INVESTIGATIONS
Dermoscopy: warts appear to be embedded in the skin, rather than "pasted on," and are gray-brown or flesh-colored, while seborrheic keratosis can be tan, brown, or black.
Nevus
SIGNS / SYMPTOMS
Most nevi develop during the first 20 years of life; seborrheic keratoses usually develop in people older than 30 years and become more common with advancing age.[9]
INVESTIGATIONS
Dermoscopy may show a homogeneous or reticular or globular pattern, or a combination of these patterns.
Pigmented basal cell carcinoma
SIGNS / SYMPTOMS
Arise on sun-exposed areas of light-skinned individuals, most frequently on the head and neck.[32] Lesions commonly occur in older adults (fourth decade and older). Clinical characteristics vary with the histopathologic subtypes. The most common type of basal cell carcinoma is the nodular basal cell carcinoma. Characteristic symptoms of nodular basal cell carcinoma are bleeding and crusting.
The second most frequent subtype of basal cell carcinoma is the superficial basal cell carcinoma. Morpheaform/infiltrative/sclerosing basal cell carcinomas are more infrequent than the other subtypes but more aggressive and locally destructive. They have a depressed, whitish scar-like appearance.[32]
INVESTIGATIONS
Dermoscopy, biopsy. Nodular basal cell carcinoma appears as well-circumscribed pearly pink or translucent papule with varying degree of pigmentation. Often well-demarcated telangiectatic vessels are seen on the surface.
Superficial basal cell carcinoma appears as an erythematous scaly plaque or patch, most commonly found on the torso.
Squamous cell carcinoma and Bowen disease
SIGNS / SYMPTOMS
Squamous cell carcinoma appears as hyperkeratotic, superficially erosive or ulcerated plaques or papules on severe sun-damaged skin.
INVESTIGATIONS
Dermoscopy: appears as hyperkeratotic, superficially erosive or ulcerated plaques or papules.
Benign neoplasias
SIGNS / SYMPTOMS
May be associated with a high number of seborrheic keratosis lesions.
INVESTIGATIONS
Tumors visible with imaging; tests for tumor markers.
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