Derm Cases · Dermatology / Procedural skills / Dermatopathology interface
OSCE — choose the right skin biopsy: technique, site, and fixative
An 8-minute OSCE station on selecting punch, shave, excisional, or incisional biopsy by indication; never shaving suspected melanoma; site selection at the active edge; and correct fixatives (formalin H&E vs Michel's medium for DIF).
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Study tools
Target exams
NEET-PGINICETUSMLEPLABMRCP
Prompt
An 8-minute OSCE station on selecting punch, shave, excisional, or incisional biopsy by indication; never shaving suspected melanoma; site selection at the active edge; and correct fixatives (formalin H&E vs Michel's medium for DIF).
Brief (to candidate)
You are in a procedure room with three patients scheduled: (A) suspected melanoma on the calf, (B) bullous rash needing DIF, (C) chronic inflammatory plaque on the trunk. A junior asks which biopsy and which bottle for each. You have 8 minutes to choose technique, site, and fixative correctly and prevent unfixable errors.
[1]Candidate instructions
- Match punch / shave / excisional / incisional to indication.
- State why shave is forbidden for suspected melanoma.
- Choose site (active edge, ulcer edge, fresh blister, not ulcer centre).
- Assign 10% formalin vs Michel's medium for DIF.
- Outline basic procedural safety (tension lines, crush artefact, labelling).
Examiner checklist (mark each domain / 10)
| Domain | Key actions expected |
|---|---|
| Technique map | Punch 3–4 mm full-thickness = inflammatory / alopecia / blistering (paired DIF); shave/saucerisation = raised benign / superficial BCC only; excisional ellipse 1–3 mm clinical margin = suspected melanoma; incisional = large lesions or deep processes (panniculitis)[1][2] |
| Melanoma rule | Never shave suspected melanoma — loses Breslow depth, staging, and margin planning; prefer full-thickness excisional biopsy with narrow clinical margin[3] |
| Site selection | Active edge of rash; edge of ulcer (not necrotic centre); fresh blister for DIF; alopecia often paired/comparison samples as local protocol[1] |
| Fixatives | 10% neutral buffered formalin for H&E; Michel's medium (not formalin) for DIF — formalin destroys immunoreactants and wastes the test[1][6] |
| Orientation / handling | Ellipse along resting skin tension lines; avoid forceps crush; ink/orient when margin mapping needed; correct labelling of multiple pots |
| What not to do | Curettage ± electrodesiccation is therapeutic for selected low-risk BCC — not a diagnostic substitute for high-risk facial NMSC or melanoma |
| Communication | Explain scarring, suture care, when results return, and need for possible definitive WLE after melanoma histology |
Model key actions
- Melanoma → excisional full-thickness, not shave.[3]
- Inflammatory/blistering → punch ± second sample in Michel's for DIF.[1][6]
- Never put DIF tissue in formalin.[6]
Common errors
- Shave biopsy of a pigmented lesion “to save time.”
- Biopsying ulcer centre only (slough, non-diagnostic).
- Sending DIF in formalin.
- Punch too shallow for panniculitis (misses subcutis).
- No consent discussion about scar and need for further surgery after melanoma path.
References4ShowHide
- [1]Greenwood JD, Merry SP, Boswell CL. Skin Biopsy Techniques. Primary Care, 2022.PMID 35125151
- [2]Pickett H. Shave and punch biopsy for skin lesions. American Family Physician, 2011.PMID 22046939
- [3]Ng JC, Swain S, Dowling JP, et al. The impact of partial biopsy on histopathologic diagnosis of cutaneous melanoma: a review of 218 cases. Archives of Dermatology, 2010.PMID 20231492
- [6]Kumudhini S, Pai S, Rao C, et al. A comparative study of Michel's medium versus honey as a transport medium for skin biopsy specimens for direct immunofluorescence. Journal of Cutaneous Pathology, 2019.PMID 31087406