Derm Cases · Dermatology / Pigmented lesions
OSCE — two-step dermoscopy algorithm: melanocytic vs non-melanocytic and melanoma clues
An 8-minute OSCE station on dermatoscope use, the two-step algorithm, vessel and pattern lexicon, acral/facial/nail special-site rules, and biopsy thresholds when dermoscopy is high-risk.
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Target exams
NEET-PGINICETUSMLEPLABMRCP
Prompt
An 8-minute OSCE station on dermatoscope use, the two-step algorithm, vessel and pattern lexicon, acral/facial/nail special-site rules, and biopsy thresholds when dermoscopy is high-risk.
Brief (to candidate)
You are given a handheld dermatoscope and clinical photos of: (A) a facial pigmented macule, (B) a plantar pigmented macule, (C) a pearly facial papule, and (D) a changing trunk naevus with blue-white structures. You have 8 minutes to demonstrate the two-step approach, name key patterns, and decide management for each.
[13]Candidate instructions
- Explain polarised vs non-polarised contact dermoscopy basics.
- Apply Step 1: melanocytic vs non-melanocytic criteria.
- Apply Step 2 melanoma-specific clues / checklist concepts.
- State special-site rules (acral ridge vs furrow; facial lentigo maligna structures; nail micro-Hutchinson).
- Map classic patterns to BCC, SK, Bowen vessels.
- Decide biopsy vs monitor safely.
Examiner checklist (mark each domain / 10)
| Domain | Key actions expected |
|---|---|
| Instrumentation | Contact dermoscopy ~10×; non-polarised needs immersion fluid to reduce glare; polarised helps vessels/collagen; both used in practice[4] |
| Two-step algorithm | Step 1: pigment network / aggregated globules / streaks / homogeneous blue / parallel pattern → melanocytic; else non-melanocytic algorithms; Step 2: melanoma vs naevus using chaos and clues or checklists (Menzies, 7-point, ABCD dermoscopy)[4][7][8] |
| Melanoma clues | Atypical network, blue-white veil, regression, irregular streaks/dots, polymorphous vessels, multicomponent chaos — biopsy rather than indefinite observation[4][8] |
| Non-melanocytic classics | BCC: arborising vessels, blue-grey ovoid nests, leaf-like/spoke-wheel; SK: milia-like cysts, comedo-like openings, cerebriform; Bowen: glomerular vessels; vessels lexicon high-yield for exams[5][4] |
| Special sites | Acral: parallel ridge = melanoma until proven otherwise; furrow/lattice/fibrillar usually benign; face: asymmetric pigmented follicular openings, rhomboids → lentigo maligna pathway; nail: micro-Hutchinson + single-digit melanonychia → matrix biopsy pathway[11][12] |
| Beyond tumours | Inflammoscopy (e.g. psoriasis dotted/glomerular vessels) and trichoscopy/entomodermoscopy extend technique; AI aids but does not replace clinicopathologic judgement[10][9] |
| Safety | Any high-risk dermoscopic pattern or ugly-duckling evolution → histology; do not reassure on pattern alone if clinical suspicion high |
Model key actions
- Demonstrate two-step reasoning lesion-by-lesion with correct special-site rules.[4][11][12]
- Flag parallel ridge, polymorphous vessels, blue-white veil, facial LM structures as biopsy triggers.[8]
- Assign arborising vessels to BCC pathway rather than melanocytic overcall.[5]
Common errors
- Calling acral ridge pattern benign.
- Observing chaos/blue-white structures indefinitely.
- Confusing BCC arborising vessels with "just telangiectasia" of rosacea without context.
- Using only ABCDE clinical rules and never dermatoscope in a pigmented-lesion station.
- Over-trusting AI or a single benign feature while ignoring evolution.
References9ShowHide
- [4]Yélamos O, Braun RP, Liopyris K, et al. Dermoscopy and dermatopathology correlates of cutaneous neoplasms. Journal of the American Academy of Dermatology, 2019.PMID 30321581
- [5]Heath MS, Bar A. Basal Cell Carcinoma. Dermatologic Clinics, 2023.PMID 36410973
- [7]Nachbar F, Stolz W, Merkle T, et al. ABCD rule of dermatoscopy: high prospective value in the diagnosis of doubtful melanocytic skin lesions. Journal of the American Academy of Dermatology, 1994.PMID 8157780
- [8]Carrera C, Marchetti MA, Dusza SW, et al. Validity and Reliability of Dermoscopic Criteria Used to Differentiate Nevi From Melanoma: A Web-Based International Dermoscopy Society Study. JAMA Dermatology, 2016.PMID 27074267
- [9]Esteva A, Kuprel B, Novoa RA, et al. Dermatologist-level classification of skin cancer with deep neural networks. Nature, 2017.PMID 28117445
- [10]Sgouros D, Apalla Z, Ioannides D, et al. Dermoscopy of Common Inflammatory Disorders. Dermatologic Clinics, 2018.PMID 30201145
- [11]Koga H, Saida T. Key points in dermoscopic differentiation between early acral melanoma and acral nevus. Journal of Dermatology, 2011.PMID 21175752
- [12]Thomas L, Phan A, Pralong P, et al. Special locations dermoscopy: facial, acral, and nail. Dermatologic Clinics, 2013.PMID 24075549
- [13]Feuerman H, Atzmony L, Glick M, et al. Pigmented demodicidosis - an under-recognized cause of facial hyperpigmentation Int J Dermatol, 2022.PMID 34897670