Seborrhoeic keratosis
SK; seborrhoeic wart; basal cell papilloma (older British term); senile wart; "stuck-on" wart
The seborrhoeic keratosis is by a wide margin the commonest benign cutaneous tumour seen by dermatologists, plastic surgeons and primary-care clinicians, and is the single most clinically important mimic of melanoma, dysplastic naevus and pigmented basal cell carcinoma in skin oncology practice. The classical lesion is a well-circumscribed, "stuck-on" pink-tan to brown to black papule or plaque with a verrucous, waxy, cerebriform or smooth surface, occurring in essentially all adults from age 40 onwards on sun-exposed and occluded skin. Dermoscopy is highly diagnostic — milia-like cysts, comedo-like openings, fissures and ridges, hairpin vessels and a sharp circumscription distinguish almost all seborrhoeic keratoses from melanocytic and basal-cell tumours. The sign of Leser-Trélat — abrupt eruption of many new SKs with pruritus — is a rare and debated paraneoplastic association, reported most often with gastrointestinal adenocarcinoma and strengthened by co-existing malignant acanthosis nigricans, tripe palms or constitutional symptoms. Treatment is generally cosmetic and unnecessary; histology is mandatory whenever there is any clinical or dermoscopic uncertainty.
Clinical features
- Well-circumscribed, "stuck-on" papule or plaque, 0.5–3 cm, sometimes pedunculated.
- Surface — waxy, verrucous, cerebriform, friable; occasionally smooth.
- Colour — flesh-pink to tan, brown, very dark brown or black (the latter is the most common diagnostic confusion with melanoma).
- Distribution — face, trunk, extremities; absent on palms and soles.
- Often multiple, frequently dozens to hundreds in older adults.
- Onset typically from the fourth decade; almost universal by the seventh.
- Variants — stucco keratosis (small white plaques on shins), dermatosis papulosa nigra (small black papules on the face of patients with darker skin), inverted follicular keratosis (face, related entity), melanoacanthoma (heavily pigmented variant).
Dermoscopy (the discriminator)
- Milia-like cysts — small white round structures (intra-epidermal keratin pseudocysts).
- Comedo-like openings — yellow-brown round structures (keratin-filled invaginations).
- Fissures and ridges — "brain-like" / cerebriform / mountain-and-valley pattern.
- Hairpin vessels with hyperkeratotic surrounding halo.
- Sharp demarcation from surrounding skin — well-defined "moth-eaten" border.
- Absent — pigment network, streaks, blue-white veil, irregular dots/globules (features of melanoma).
- Caveat — irritated or traumatised SKs may show vascular and reactive features, increasing the difficulty of differentiating from melanoma; biopsy if uncertain.
Critical differential diagnosis
- Melanoma — particularly nodular and pigmented superficial spreading subtypes; the single most important miss. Always biopsy if any clinical or dermoscopic doubt.
- Pigmented basal cell carcinoma — leaf-like areas, blue-grey ovoid nests, arborising vessels.
- Dysplastic naevus — symmetrical pigment network, regular dots/globules.
- Solar lentigo — flat, no surface scale; close cousin and may co-exist (lentigo → reticulated SK transition).
- Pigmented Bowen's disease — slow-growing scaly plaque, often lower limb.
- Melanoma in situ on chronically sun-damaged skin (lentigo maligna) — facial pigmentation often misdiagnosed as facial SKs.
Sign of Leser-Trélat
- Sudden eruption of multiple new seborrhoeic keratoses with associated pruritus, in a patient who has not previously had many SKs.
- Rare and debated paraneoplastic association — reported most often with adenocarcinoma of the gastrointestinal tract (gastric, colorectal, pancreatic), less often breast or genitourinary cancer or lymphoma.
- The index of suspicion is higher when eruption is truly abrupt, the patient is younger than expected, or there are co-existing paraneoplastic signs such as malignant acanthosis nigricans, tripe palms, weight loss or unexplained systemic symptoms.
- Investigation — full history and examination, FBC, U&E, LFT, age-appropriate cancer screening (mammography, FOB / colonoscopy, CT chest/abdomen/pelvis if symptoms or red flags).
- Counsel and reassure — most patients with apparent Leser-Trélat have idiopathic eruptive SKs without underlying malignancy; a balanced workup is appropriate.
Management
- Reassurance — no treatment required for the great majority of asymptomatic lesions.
- Indications for treatment: cosmetic distress, irritation, friction, bleeding, recurrent inflammation, diagnostic uncertainty.
- Modalities:
- Cryotherapy (liquid nitrogen) — quick, effective; risk of post-inflammatory hypopigmentation.
- Curettage and cautery — provides histology, good cosmesis.
- Shave excision — provides histology.
- Excision — for diagnostic concern or large lesions.
- Laser or electrodesiccation. Topical hydrogen peroxide 40% (Eskata) was a US product and is discontinued / not a routine UK option.
- Always submit for histology if any clinical or dermoscopic doubt about the diagnosis.
- Counsel patients about photoprotection (although SK is not directly UV-driven, accompanying actinic damage often warrants management).
References
- Hafner C, Vogt T. Seborrheic keratosis. J Dtsch Dermatol Ges; 2008.
- Heidenheim M, Jemec GB. Sign of Leser-Trélat — review. J Am Acad Dermatol; 1990.
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