Differentials
Malignant melanoma
SIGNS / SYMPTOMS
Malignant melanoma is the most important differential diagnosis of seborrhoeic keratosis. Sometimes differentiating between seborrhoeic keratosis and melanoma is a challenge. A key feature is that a melanoma tends to vary more in colour, such as brown, blue, black, grey, and red, whereas a seborrhoeic keratosis is usually limited to shades of brown and black.
Melanoma usually has a smooth surface that can vary in height, while seborrhoeic keratosis usually looks the same across the whole surface. Melanoma does not generally have the warty, 'stuck-on' appearance of seborrhoeic keratosis.[1][2][3][26]
Melanoma is less uniform and less symmetrical in colour and shape than seborrhoeic keratosis.
INVESTIGATIONS
Dermoscopy: dark pigmentations forming an asymmetrical ring around follicular openings, slate-grey dots and areas of irregular, broadened network. Also, biopsy and histopathological 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 grey-brown or flesh-coloured, while seborrhoeic keratosis can be tan, brown, or black.
Naevus
SIGNS / SYMPTOMS
Most nevi develop during the first 20 years of life; seborrhoeic keratoses usually develop in people older than 30 years and become more common with advancing age.
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.[2][27] Lesions commonly occur in older adults (fourth decade and older). Clinical characteristics vary with the histopathological 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.[2][27]
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's 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.
Gastrointestinal tract adenocarcinoma
SIGNS / SYMPTOMS
The Leser-Trélat sign is the appearance of a high number of seborrhoeic keratoses over a short time interval, especially on the torso.[3][5][6][7] It may be a paraneoplastic phenomenon associated with a gastrointestinal tract adenocarcinoma but this is debated in the literature.[8] It is often associated with metastatic spread of the primary tumour and with a poor prognostic outcome of the affected patients. Approximately 100 cases of Leser-Trélat have been reported in the literature. The seborrhoeic keratosis may precede, follow, or develop concurrently with the beginning of the symptoms of the cancer. Involution of the seborrhoeic keratoses after successful treatment of the cancer has been described.
INVESTIGATIONS
Tumours visible with imaging; tests for tumour markers.
Lymphoproliferative disorders
Benign neoplasias
SIGNS / SYMPTOMS
May be associated with a high number of seborrhoeic keratosis lesions.
INVESTIGATIONS
Tumours visible with imaging; tests for tumour markers.
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