Seborrheic keratosis can arise anywhere on the skin, sun-exposed or non-exposed, with the exception of palms and soles. Mostly they are papules or plaques that are few millimeters or centimeters wide. Their color may range from yellow to skin color to brown and black. They have a smooth, waxy warty appearance. They can be singly located or may appear in groups (Oakley 2017).
Dermoscopy: Irregular structure with carrying colors. Irregular crypts, fissure or ridges are seen. Blue-grey globules and finger-print like parallel structures can be seen.
Since non-polarized light penetrates the skin superficially it is preferred in looking at SK (Benvenuto-Andrade et al. 2007), (2017b).
Histopathology: acanthotic proliferations of keratinocytes without cytological atypia. Round Intralesional loose keratin cysts are present. String sign can be appreciated sometimes which is drawing of a horizontal line parallel to the epidermal surface underlying the lesion (Elwood 2017). There are 6 subtypes of SK. However mostly more than one are found in any lesion biopsied.
Differential diagnoses: Differential is almost always made by pathology however dermoscopy has helped in this regard and is point of the care differentiating tool (2017).
- Melanoma: ABCD is followed to diagnose. Melanomas are usually darkly pigmented lesions with asymmetric rings around follicular openings with irregular broadened network.
- Viral warts: Usually have a buried appearance rather than stuck on appearance. Mostly flesh colored as compared to SK’s tan, brown, black color.
- Nevus: Shows homogenous, reticular, globular or mixed pattern of pigmentation.
- Pigmented Basal Cell Carcinoma (BCC): well-circumscribed, pearly, pink or translucent papule with varying degreeing of pigmentation and telangiectasias.
- Squamous cell carcinoma (SCC): Superficially erosive, ulcerative and hyperkeratotic papules.
Benvenuto-Andrade et al. 2007. Differences Between Polarized Light Dermoscopy and Immersion Contact Dermoscopy for the Evaluation of Skin Lesions. Archives of Dermatology 143(3), pp. 329–338. doi: 10.1001/archderm.143.3.329.
Elwood 2017. Pathology Outlines – Seborrheic keratosis. Available at: http://www.pathologyoutlines.com/topic/skintumornonmelanocyticSK.html.
Oakley 2017. Seborrhoeic keratosis | DermNet New Zealand. Available at: https://www.dermnetnz.org/topics/seborrhoeic-keratosis/.
2017a. Dermoscopy for the Family Physician – American Family Physician. Available at: http://www.aafp.org/afp/2013/1001/p441.html.
2017b. Seborrheic keratosis Differential Diagnosis – Epocrates Online. Available at: https://online.epocrates.com/diseases/61735/Seborrheic-keratosis/Differential-Diagnosis.