Derm Cases · Dermatology / Laser Medicine
OSCE — dermatologic lasers: selective photothermolysis, chromophore matching, and safety
An 8-minute OSCE station on selective photothermolysis, matching laser/wavelength to chromophore (melanin, haemoglobin, water, ink), pre-treatment safety (isotretinoin, eye protection), and choosing modalities for hair, vessels, pigment and scars.
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NEET-PGINICETUSMLEPLABMRCP
Prompt
An 8-minute OSCE station on selective photothermolysis, matching laser/wavelength to chromophore (melanin, haemoglobin, water, ink), pre-treatment safety (isotretinoin, eye protection), and choosing modalities for hair, vessels, pigment and scars.
Brief (to candidate)
A 30-year-old Fitzpatrick IV woman wants laser hair reduction on the face and treatment of a port-wine stain on her cheek. She finished oral isotretinoin 1 month ago and tans weekly. You have 8 minutes to explain laser principles, choose appropriate devices, and counsel safety and realistic outcomes.
[9]Candidate instructions
- State the principle of selective photothermolysis.
- Match chromophores (melanin, haemoglobin, water, tattoo ink) to common lasers.
- Choose modalities for hair, vascular, pigment, resurfacing.
- List contraindications/cautions (recent isotretinoin, active infection, unrealistic goals, eye safety).
- Counsel skin of colour risks (PIH, burns).
Examiner checklist (mark each domain / 10)
| Domain | Key actions expected |
|---|---|
| Selective photothermolysis | Preferential thermal injury to target chromophore when wavelength, pulse duration ≤ thermal relaxation time, and fluence adequate — spares surrounding tissue if parameters correct[1] |
| Chromophore map | Melanin — hair reduction (e.g. alexandrite 755, diode ~800–810, Nd:YAG 1064 better deeper/darker skin); haemoglobin — PDL ~585–595 for vascular; water — ablative/fractional resurfacing (Er:YAG/CO₂); ink — Q-switched/picosecond multi-wavelength tattoo lasers[2][5][9][11] |
| Hair removal | Works best on dark terminal hair / lighter skin; multiple sessions; Nd:YAG preferred when higher epidermal melanin risk; not permanent “one session” cure[2] |
| Vascular / PWS | Pulsed dye laser first-line many port-wine stains; multiple treatments; counsel incomplete clearance possible; eye protection critical near orbit[9][14] |
| Safety / isotretinoin | Recent isotretinoin historically delayed ablative procedures due to scarring concerns — follow current cautious protocols; avoid treating tanned skin; test spots in skin of colour; mandatory wavelength-specific eyewear[8] |
| Complications | Burns, blistering, PIH/hypopigmentation, scarring, paradoxical hypertrichosis (hair lasers), ocular injury if inadequate protection |
| Communication | Consent: sessions needed, downtime, pigment risk in Fitzpatrick IV–VI, sun avoidance peri-procedure |
Model key actions
- Explain selective photothermolysis and pick Nd:YAG or appropriate hair laser carefully in skin of colour; PDL for port-wine stain.[1][2][9]
- Defer aggressive ablative resurfacing soon after isotretinoin per protocol; enforce eye safety and no active tan.[8]
- Counsel multi-session expectations and PIH risk.[10]
Common errors
- Claiming permanent complete hair removal in one session.
- Using short-wavelength lasers aggressively on tanned/dark skin without PIH counselling.
- No eye protection plan near facial treatments.
- Treating through active infection or unrealistic vascular clearance promises.
- Ignoring recent isotretinoin before ablative procedures.
References8ShowHide
- [1]Anderson RR, Parrish JA. Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation. Science, 1983.PMID 6836297
- [2]Gan SD, Graber EM. Laser hair removal: a review. Dermatologic surgery : official publication for American Society for Dermatologic Surgery [et al.], 2013.PMID 23332016
- [5]Gurnani P, Williams N, Al-Hetheli G, et al. Comparing the efficacy and safety of laser treatments in tattoo removal: A systematic review. Journal of the American Academy of Dermatology, 2022.PMID 32763326
- [8]Khatri KA, Iqbal N, Bhawan J. Laser skin resurfacing during isotretinoin therapy. Dermatologic surgery : official publication for American Society for Dermatologic Surgery [et al.], 2015.PMID 25993614
- [9]Shi MD, Yang K, Li SB, et al. Complication rates and safety of pulsed dye laser treatment for port-wine stain: a systematic review and meta-analysis. Lasers in medical science, 2023.PMID 38141129
- [10]Sowash M, Alster T. Review of Laser Treatments for Post-Inflammatory Hyperpigmentation in Skin of Color. American journal of clinical dermatology, 2023.PMID 36781686
- [11]Wu DC, Goldman MP, Wat H, et al. A Systematic Review of Picosecond Laser in Dermatology: Evidence and Recommendations. Lasers in surgery and medicine, 2021.PMID 32282094
- [14]Sebaratnam DF, Rodríguez Bandera AL, Wong LF, et al. Infantile hemangioma. Part 2: Management. Journal of the American Academy of Dermatology, 2021.PMID 34419523