Seborrhoeic Keratosis: A benign, warty spot that appears during adult life and is a common sign of skin aging. Some individuals may have hundreds of them.
Synonyms
Other Names: SK, basal cell papilloma, senile wart, brown wart, wisdom wart, barnacle.
Broader Term: Benign keratosis, which includes related scaly skin lesions:
Seborrhoeic keratosis
Solar lentigo (can be difficult to distinguish from flat seborrhoeic keratosis)
Lichen planus-like keratosis (arises from a seborrhoeic keratosis or a solar lentigo)
Prevalence
Commonality: Extremely common.
Estimates: Over 90% of adults over the age of 60 have one or more lesions.
Age of Onset: Typically begins in the 30s or 40s, uncommon under the age of 20.
Gender and Race: Occurs in both males and females of all races.
Causes
Unknown Cause: The precise cause of seborrhoeic keratoses is not known.
Misleading Name: Not limited to seborrhoeic distribution or related to sebaceous glands or sebum.
Degenerative Nature: They become more numerous with age.
Genetic Factors: Some people inherit a tendency to develop a large number of lesions.
Possible Triggers:
Sunburn or dermatitis can lead to eruptive seborrhoeic keratoses.
Skin friction may cause them to appear in body folds.
Viral cause (e.g., human papillomavirus) is unlikely.
Genetic mutations: Stable and clonal mutations or activation of FGFR3, PIK3CA, RAS, AKT1, and EGFR genes.
Associations:
Solar lentigo can evolve into seborrhoeic keratosis.
FGFR3 mutations also occur in solar lentigines, suggesting a role of UV radiation.
Not associated with tumor suppressor gene mutations.
Location: Can arise on any skin area except palms and soles. Not found on mucous membranes.
Appearance: Highly variable.
Size: From 1 mm to several cm in diameter.
Color: Skin-colored, yellow, grey, light brown, dark brown, black, or mixed.
Surface Texture: Smooth, waxy, or warty.
Distribution: Solitary or grouped, often found in the scalp, under the breasts, over the spine, or in the groin.
Adhesion: Appear to stick to the skin surface like barnacles.
Variants of Seborrhoeic Keratoses
Solar Lentigo: Flat, circumscribed pigmented patches in sun-exposed areas.
Dermatosis Papulosa Nigra: Small, pedunculated, heavily pigmented lesions, common on the head and neck of darker-skinned individuals.
Stucco Keratoses: Grey, white, or yellow papules, usually on the lower extremities.
Inverted Follicular Keratosis
Large Cell Acanthoma
Lichenoid Keratosis: An inflammatory phase preceding the involution of some seborrhoeic keratoses and solar lentigines.
Complications
Non-Premalignant: Seborrhoeic keratoses are not premalignant tumors.
Cancer Confusion: Skin cancers can be difficult to differentiate from seborrhoeic keratoses.
Rare Associations:
Eruptive seborrhoeic keratoses may rarely indicate an underlying internal malignancy (e.g., gastric adenocarcinoma), known as the sign of Leser-Trélat.
Eruptive lesions not associated with cancer may be termed pseudo-sign of Leser-Trélat.
Medications (e.g., adalimumab, vemurafenib, dabrafenib, 5-fluorouracil, chemotherapy drugs) can cause eruptive or irritated lesions.
Diagnosis
Typical Diagnosis: Often straightforward based on appearance.
Common Features: Stuck-on, well-demarcated warty plaques with other similar lesions.
Resemblance to Skin Cancer: May resemble basal cell carcinoma, squamous cell carcinoma, or melanoma.
Dermoscopy: Shows a disordered structure. Diagnostic clues include:
Multiple orange or brown clods (due to keratin)
White milia-like clods
Curved thick ridges and furrows forming a brain-like pattern
Biopsy: Partial shave or punch biopsy if diagnosis is uncertain.
Histopathology
Histopathological Features: May include:
Melanoacanthoma (deeply pigmented)
Acanthotic
Hyperkeratotic or papillomatous
Adenoid or reticulated
Clonal or nested
Adamantinoid or mucinous
Desmoplastic
Irritated
Treatment
Removal Indications: Unsightly appearance, itchiness, or catching on clothing.
Methods:
Cryotherapy (liquid nitrogen) for thinner lesions
Curettage and/or electrocautery
Ablative laser surgery
Shave biopsy (scalpel removal)
Focal chemical peel with trichloracetic acid
Disadvantages: Each method has potential drawbacks, including pigmentation loss, particularly in dark-skinned individuals.
Multiple Lesions: No easy method to remove multiple lesions simultaneously.
Prevention
Unknown: No known methods to prevent seborrhoeic keratoses.
Outlook
Persistence: Lesions tend to persist.
Remission: Individual or multiple lesions may remit spontaneously or via the lichenoid keratosis mechanism.
Dermatitis-Associated Regression: Lesions associated with dermatitis may regress after controlling dermatitis.
