Derm Cases · Dermatology / Paediatrics / Genetics / Dermato-oncology
OSCE — Blaschkoid warty plaque and scalp naevus sebaceous: mosaicism and Schimmelpenning
An 8-minute OSCE station on epidermal naevi along Blaschko lines, naevus sebaceous natural history and secondary tumour risk, conservative modern management, and epidermal naevus syndrome red flags.
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Study tools
Target exams
NEET-PGINICETUSMLEPLABMRCP
Prompt
An 8-minute OSCE station on epidermal naevi along Blaschko lines, naevus sebaceous natural history and secondary tumour risk, conservative modern management, and epidermal naevus syndrome red flags.
Brief (to candidate)
Parents present two children: (A) a linear warty Blaschkoid plaque on the limb present since infancy; (B) a yellow-orange hairless scalp plaque that is becoming thicker at puberty. They were told all naevus sebaceous must be excised in infancy for cancer. You have 8 minutes to classify, counsel true risks, and screen for epidermal naevus syndrome.
Candidate instructions
- Explain epidermal naevi as mosaic hamartomas along Blaschko lines.
- Distinguish keratinocytic EN vs naevus sebaceous.
- Update secondary neoplasm risk and modern conservative care for NS.
- Flag Schimmelpenning / ENS extracutaneous disease.
- Manage new nodules within NS.
Examiner checklist (mark each domain / 10)
| Domain | Key actions expected |
|---|---|
| Concept | Congenital/early hamartomas from postzygotic mosaicism following Blaschko lines (not dermatomes)[6] |
| Keratinocytic EN | Linear verrucous/warty plaques; ILVEN pruritic psoriasiform variant; treatment cosmetic/symptomatic (topicals, laser, excision) with recurrence possible after superficial destruction[5][6] |
| Naevus sebaceous | Yellow-orange alopecic scalp/face plaque; thickens/verrucous at puberty; HRAS/KRAS mosaic pathway classically; secondary tumours (trichoblastoma, syringocystadenoma, less commonly BCC) possible — biopsy changing nodules[6][9] |
| Management myth | Routine prophylactic infant excision of all NS not mandatory in modern practice for low absolute cancer risk — surveillance ± elective excision for cosmesis/change; shared decision with parents |
| ENS / Schimmelpenning | Extensive head/neck NS or EN + seizures, developmental delay, ocular/skeletal anomalies, hypophosphataemic rickets → multidisciplinary genetics/neuro/ortho/ophth work-up[3][6] |
| Genetics counselling pearl | Epidermolytic EN (KRT1/10) may imply gonadal mosaicism risk of generalised epidermolytic ichthyosis in offspring — specialised counselling |
| Communication | Correct "must cut out every NS at birth for cancer" absolute myth while not dismissing nodule change |
Model key actions
- Diagnose Blaschkoid epidermal naevus and naevus sebaceous correctly.[6]
- Prefer surveillance for uncomplicated NS; biopsy new nodules.[6]
- Screen ENS when neurologic/skeletal/ocular features coexist.[3]
Common errors
- Mandatory infant excision of all NS "to prevent cancer."[9]
- Ignoring seizures/developmental delay as ENS clues.
- Confusing Blaschko lines with dermatomes (zoster).
- Missing secondary neoplasm when a nodule appears in adult NS.
References4ShowHide
- [5]Khan W, Ibrahim A, Alvaro A, et al. Laser treatment of verrucous epidermal naevi: a systematic review. Journal of cutaneous medicine and surgery, 2022.PMID 35603930
- [6]Waldman AR, Garzon MC, Morel KD Epidermal nevi: what is new. Dermatologic clinics, 2022.PMID 34799036
- [3]Olivares JL, Ramos FJ, Carapeto FJ, et al. Epidermal naevus syndrome and hypophosphataemic rickets: description of a patient with central nervous system anomalies and review of the literature. European journal of pediatrics, 1999.PMID 10048604
- [9]Groesser L, et al. Postzygotic HRAS and KRAS mutations cause nevus sebaceous and Schimmelpenning syndrome. Nat Genet, 2012.PMID 22683711