Derm Cases · Dermatology / Benign tumours
OSCE — stuck-on waxy plaques: seborrhoeic keratosis, dermoscopy and Leser-Trélat
An 8-minute OSCE station on seborrhoeic keratosis recognition, dermoscopic criteria, melanoma mimics, cosmetic options, and the Sign of Leser-Trélat.
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Target exams
NEET-PGINICETUSMLEPLABMRCP
Prompt
An 8-minute OSCE station on seborrhoeic keratosis recognition, dermoscopic criteria, melanoma mimics, cosmetic options, and the Sign of Leser-Trélat.
Brief (to candidate)
A 64-year-old woman is worried about multiple tan–brown “stuck-on” waxy plaques on her trunk and face. One dark irregular lesion worries her after a friend had melanoma. Separately she reports a sudden crop of dozens of new itchy lesions over 2 months with weight loss. You have 8 minutes to diagnose typical SK, use dermoscopy concepts, plan management, and recognise Leser-Trélat.
Candidate instructions
- Describe classic seborrhoeic keratosis morphology (“stuck-on”, waxy/verrucous).
- List key dermoscopy features and how they differ from melanoma.
- State that SK is benign / not premalignant.
- Outline cosmetic options (cryotherapy, curettage, shave, topical options).
- Explain Sign of Leser-Trélat and appropriate malignancy work-up.
- When to biopsy despite a clinical SK label.
Examiner checklist (mark each domain / 10)
| Domain | Key actions expected |
|---|---|
| Recognition | Well-demarcated oval stuck-on waxy/verrucous tan–brown–black plaques — “barnacles of ageing”; commonest benign epidermal tumour[1][3][4] |
| Dermoscopy | Milia-like cysts, comedo-like openings, fissures/ridges (cerebriform/brain-like), fingerprint structures, sharp border; no melanocytic pigment network / no arborising vessels of BCC — but acknowledges dermoscopy limitations and false security[1][6] |
| Biology / counsel | Benign clonal keratinocyte proliferation (FGFR3-associated in many); not premalignant; leave alone if asymptomatic and confident diagnosis[1][3] |
| Treatment options | Cryotherapy, curettage, shave excision, laser; topical hydrogen peroxide 40% / other topicals for selected cosmetic cases; set scar/pigment expectations[2][4] |
| Leser-Trélat | Sudden eruption of numerous pruritic SKs ± acanthosis nigricans → paraneoplastic association (classically gastric adenocarcinoma / haematologic malignancy) → systemic evaluation and GI work-up as indicated[5] |
| Biopsy triggers | Dark, irregular, evolving, bleeding, ulcerated, or diagnostically uncertain lesions — biopsy to exclude melanoma / SCC; never “assume SK” for ugly pigmented lesions[6] |
| Communication | Reassure about typical stable SK; escalate urgent work-up for eruptive/pruritic crop with constitutional symptoms |
Model key actions
- Diagnose typical trunk/face seborrhoeic keratoses and offer observation vs cosmetic removal.[1][4]
- Use dermoscopy language but biopsy the irregular dark lesion if any doubt.[6]
- Flag Leser-Trélat for the sudden pruritic crop + weight loss and arrange malignancy screen.[5]
Common errors
- Labeling every brown plaque SK without dermoscopy/biopsy when irregular.
- Calling SK “pre-cancer” and causing unnecessary anxiety.
- Missing Leser-Trélat as a paraneoplastic signal.
- Over-treating asymptomatic lesions with high risk of pigment change.
- Confusing pigmented SK with melanoma and delaying specialist referral.
References6ShowHide
- [1]Barthelmann S, Butsch F, Lang BM, et al. Seborrheic keratosis. Journal der Deutschen Dermatologischen Gesellschaft = Journal of the German Society of Dermatology : JDDG, 2023.PMID 36892019
- [2]Natarelli N, Krenitsky A, Hennessy K, et al. Efficacy and safety of topical treatments for seborrheic keratoses: a systematic review. The Journal of dermatological treatment, 2023.PMID 36215682
- [3]Hafner C, Vogt T. Seborrheic keratosis. Journal der Deutschen Dermatologischen Gesellschaft = Journal of the German Society of Dermatology : JDDG, 2008.PMID 18801147
- [4]Wilson JL. Benign Skin Tumors. Primary Care, 2025.PMID 40835288
- [5]Rowe B, Yosipovitch G. Paraneoplastic Itch Management. Current problems in dermatology, 2016.PMID 27578084
- [6]Papageorgiou V, Apalla Z, Sotiriou E, et al. The limitations of dermoscopy: false-positive and false-negative tumours. Journal of the European Academy of Dermatology and Venereology : JEADV, 2018.PMID 29314288