Seborrheic keratoses are common, benign epidermal tumors that present as well-demarcated, “stuck-on,” waxy papules or plaques with variable pigmentation. They arise in adulthood and increase with age. While asymptomatic, SKs can itch, become irritated, or cosmetically concerning. The primary clinical challenge is distinguishing SKs from malignant mimickers, especially melanoma and pigmented basal cell carcinoma. Diagnosis is clinical supported by dermoscopy; biopsy is reserved for atypical lesions. Treatments are elective for symptoms or cosmesis and include cryotherapy, curettage/shave removal, electrodessication, and topical hydrogen peroxide 40% solution for raised lesions.
Epidemiology and Risk Factors
- Very common after age 40; prevalence increases with age.
- Occur in all skin types; pigmentation pattern varies with skin tone.
- Genetics (FGFR3, PIK3CA mutations) implicated; sun exposure may contribute to distribution on photo-exposed sites.
Clinical Features
- “Stuck-on,” verrucous/waxy papules or plaques; colors range from light tan to dark brown/black.
- Surface features: keratin pseudocysts (milia-like cysts), fissures/ridges, crumbly/greasy scale.
- Locations: trunk, face, scalp, extremities; classically spare palms/soles.
- Variants: dermatosis papulosa nigra (multiple small dark facial SKs in skin of color), stucco keratoses (white-gray papules on lower legs/feet), irritated SK (erythematous, crusted), reticulated/adenoid types.
Differential Diagnosis
- Melanoma (especially flat, dark, irregular lesions), pigmented BCC, solar lentigo, warts, lichenoid keratosis, acanthosis nigricans, epidermal nevi.
- “Leser–Trélat sign”: sudden eruption of multiple pruritic SKs may rarely signal internal malignancy; evidence mixed—consider age-appropriate cancer screening and clinical context.
Diagnosis
- Clinical with dermoscopy: multiple milia-like cysts, comedo-like openings, fissures/ridges (cerebriform), moth-eaten borders, hairpin vessels with white halos in irritated lesions.
- Biopsy if atypical features: asymmetry, irregular pigment network, blue-black areas, ulceration, bleeding, rapid change, or if differentiation from melanoma/BCC is uncertain.
Management
- Observation: benign with no malignant potential.
- Symptomatic/cosmetic removal:
- Cryotherapy with liquid nitrogen (short freeze for flat/raised lesions; risk of hypopigmentation, particularly in darker skin).
- Curettage or tangential shave excision ± light electrodessication.
- Electrodessication alone for small lesions.
- Hydrogen peroxide 40% topical solution for raised SKs (multiple sessions; stinging/erythema common).
- Post-procedure care: petrolatum and gentle cleansing; counsel on PIH risk in skin of color and potential hypopigmentation after cryo.
Patient Counseling
- Benign nature; monitor for ABCDE changes.
- Sun protection and skin self-exams; return for evaluation of changing or symptomatic lesions.
References (recent guidelines and reviews)
- Dermoscopy of SK and melanoma mimics, 2021–2024.
- Procedural outcomes for SK removal and topical hydrogen peroxide 40% data, 2021–2024.