SEBORRHEIC KERATOSIS

Seborrheic keratosis (SK) is the most common of all benign skin tumors. These lesions are neoplasms of epidermal cells that appear as scaling, “pasted on” papules or plaques. They occur most commonly on the head, neck, trunk, and extremities, while the palms and solesare typically spared. SKs are gradually acquired in middle age and grow slowly later in life, being present on the skin of most older adults. In some cases, SKs can be mistaken for other potentially malignant skin diseases, such as melanoma, basal cell carcinoma, and squamous cell carcinoma.^1-4

Pathophysiology

• SKs are regarded as a sign of aging, and their pathogenesis is not completely understood. One suggested theory is that these lesions result from the clonal expansion of a mutated epidermal keratinocyte.
  • Mutations in genes related to tumor development in epidermal skin cells have been found for both SK and squamous cell carcinoma. Molecularly, high expression and activity of fibroblast growth factor receptor-33 and Akt4 appears to be necessary for development of SK but not squamous cell carcinoma.^1,4
  • SKs are also believed to be an autosomal dominant inherited trait, with many patients reporting a family history. Ultraviolet radiation may also play a role in the development of some SKs, with recent suggestion that seborrheic keratoses may lie on a spectrum that includes solar lentigines.^1,2

Related Anatomy

• Dermis
• Epidermis
• Epidermal cells
• Keratin
• SKs can be classified into one of the following six subtypes: 
  • Hyperkeratotic type
  • Acanthotic type
  • Reticular/adenoid type
  • Clonal type
  • Irritated type
  • Melanoakanthoma¹

Incidence and Related Conditions

• SK ranks as one of the top five most common skin disorders seen by dermatologists.⁴
• SKs usually begin to appear in middle age and become more common in older age, with 80-100% of individuals aged ≥50 years having at least one SK lesion.^2,4
• Actinic keratosis
• Keratosis follicularis
• Stucco keratosis

Differential Diagnosis

• Basal cell carcinoma
• Melanoma
• Melanocytic nevus
• Squamous cell carcinoma 
• Wart 

A typical patient is an 86-year-old woman who recently came under the care of a new geriatrician. During her annual checkup, the geriatrician examined the woman’s skin and noticed a number of SKs in several locations, including the dorsum of both hands. The lesions were primarily tan-colored and ovular, only slightly elevated, and measured at ~1-2 cm each. When asked about the SKs, the woman reported first noticing them in her late 30s, and that the lesions had continued to grow in number and size since then, but had not caused her any issues.

• Irritation
• Bleeding
• Discomfort
• Sign of Leser-Trélat: sudden increase in size and number of SKs accompanied by pruritis; described as a paraneoplastic syndrome in patients with internal malignancy²

• In most cases SKs do not resolve (some will enlarge, many will not change)
• In a small trial that compared cryotherapy to curettage, patients preferred cryotherapy and physicians observed more redness and a tendency for hypopigmented scar formation at follow-ups with curettage.¹

• When typical SK characteristics are present (eg, light brown to brown nodule with a papillomatous and/or scaly surface), diagnosis through the skin examination is typically straightforward; however, variations in presentation can resemble the appearance of malignant tumors and complicate the diagnosis.³
• Plaques or papules^1-3
  • Range in color from flesh to tannish brown, skin colored, or occasionally black
  • Range in size from 2 mm to 4 cm
  • Slightly to markedly elevated
  • Oval to round in shape
  • Greasy-appearing
  • “Pasted on” or “stuck-on” appearance
  • Surface often appears verrucous or crumbly and may be punctuated with keratin-filled pits
• An excisional or deep-shave biopsy may be needed for lesions that are inflamed, bleeding, ulcerated, or sufficiently irritated, and/or if a malignancy is suspected.^1,2
• Dermoscopy is often helpful for distinguishing SK from other cutaneous neoplasms based on established characteristic findings.³
• Comedo-like openings, milia-like cysts, and fissures and ridges are also characteristic.¹
• Although most SKs have a maximum diameter of <4 cm, a giant lesion may develop in some patients. Other possible differential diagnoses—such as Buschke-Löwenstein tumors—may be considered in these cases.¹

Cited Articles

1. Wollina U. Seborrheic Keratoses - The Most Common Benign Skin Tumor of Humans. Clinical presentation and an update on pathogenesis and treatment options. Open Access Maced J Med Sci 2018;6(11):2270-2275.PMID: 30559899
2. Marks JG, Miller JJ. Lookingbill and Marks’ Principles of Dermatology. Fifth Ed. London, New York: Saunders Elsevier; 2013.
3. Minagawa A. Dermoscopy-pathology relationship in seborrheic keratosis. J Dermatol 2017;44(5):518-524.PMID: 28447350
4. Hartel A, Jung T, Sift Carter R. Artemether for topical use in patients with seborrhoeic keratosis. Br J Dermatol 2018;179(5):1225-1226.PMID: 29957837
5. James WD, Berger TG, Elston DM. Andrews’ Diseases of the Skin.12^thEd. Philadelphia, PA. Elsevier, 2016.

Review

1. Karadag AS, Parish LC. The status of the seborrheic keratosis. Clin Dermatol2018;36(2):275-277. PMID: 29566932