Derm Cases · Dermatology / Benign soft-tissue tumours
OSCE — firm brown leg papule: dermatofibroma dimple sign and DFSP mimic
An 8-minute OSCE station on classic dermatofibroma morphology, dimple sign, dermoscopy, when observation is safe, and red flags that force re-consideration of DFSP or atypical fibrous histiocytoma.
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Target exams
NEET-PGINICETUSMLEPLABMRCP
Prompt
An 8-minute OSCE station on classic dermatofibroma morphology, dimple sign, dermoscopy, when observation is safe, and red flags that force re-consideration of DFSP or atypical fibrous histiocytoma.
Brief (to candidate)
A 34-year-old woman has a firm 7 mm reddish-brown papule on the shin for 2 years after a supposed insect bite. Lateral compression produces central dimpling. She asks if it is melanoma or needs excision. You have 8 minutes to diagnose dermatofibroma, explain the dimple sign, outline options, and list red flags for DFSP / atypical DF.
Candidate instructions
- Recognise classic dermatofibroma (benign fibrous histiocytoma).
- Demonstrate / explain the dimple (Fitzpatrick) sign.
- Mention common dermoscopy patterns and aneurysmal/haemosiderotic mimics of melanoma.
- State observation is appropriate for typical stable lesions.
- List indications for excision / biopsy.
- Distinguish from DFSP using clinical and IHC concepts (CD34 vs Factor XIIIa).
Examiner checklist (mark each domain / 10)
| Domain | Key actions expected |
|---|---|
| Recognition | Firm 3–10 mm reddish-brown dermal papule, often lower legs of young/middle-aged women; may follow minor trauma/insect bite history; freely mobile over subcutis but tethered to dermis/epidermis[1][2] |
| Dimple sign | Lateral compression produces central dimpling — classic bedside clue for DF |
| Dermoscopy | Peripheral delicate pigment network with central white scar-like area common; aneurysmal/haemosiderotic DF can look blue-black and mimic melanoma → biopsy if uncertain[3] |
| Management | Reassure and observe if classic and stable; optional excision for pain, catch-on clothing, cosmetics, or diagnostic doubt; scar on pretibial skin may be cosmetically significant |
| Red flags | Size >2 cm, rapid growth, plaque-like, deep fixation, recurrence after “DF” excision → rethink DFSP or atypical fibrous histiocytoma; complete excision + IHC when atypical[1] |
| IHC concept | Classic DF often Factor XIIIa+ / CD34− (or only focal CD34 at periphery); DFSP diffuse CD34+ / Factor XIIIa− — useful when histology is ambiguous |
| Communication | Benign nature; self-monitor for change; photograph if patient anxious |
Model key actions
- Diagnose typical pretibial dermatofibroma with positive dimple sign and offer observation.[1][2]
- Biopsy/excise if melanocytic concern (aneurysmal pattern) or atypical growth.[3]
- Flag DFSP pathway for large/plaque/recurrent lesions with CD34 testing.[1]
Common errors
- Excising every DF without counselling pretibial scar risk.
- Missing melanoma-like aneurysmal DF presentation.
- Calling recurrent trunk plaque “DF” without considering DFSP.
- Partial sampling of atypical fibrohistiocytic lesions.
- Over-reassuring about rapidly enlarging firm plaques.
References6ShowHide
- [1]Wan L, Park A, Almatroud L, et al. Dermatofibroma: Reappraisal and Updated Review. Clinical, cosmetic and investigational dermatology, 2025.PMID 40785832
- [2]Wilson JL. Benign Skin Tumors. Primary Care, 2025.PMID 40835288
- [3]Zaballos P, Álvarez-Salafranca M, Llambrich À, et al. Dermoscopy of haemosiderotic/aneurysmal dermatofibroma: A morphological study of 110 cases. Journal of the European Academy of Dermatology and Venereology, 2023.PMID 36251407
- [4]Jordan C, Hodges W, Russell L, et al. Dermatofibroma Hypocellularity Is Associated With Patient Age: A Retrospective Study of 307 Cases. Journal of Cutaneous Pathology, 2026.PMID 42252143
- [5]Felty CC, Linos K. Epithelioid Fibrous Histiocytoma: A Concise Review. The American Journal of Dermatopathology, 2019.PMID 30289773
- [6]Stanoszek LM, Wang GY, Harms PW. Histologic Mimics of Basal Cell Carcinoma. Archives of Pathology and Laboratory Medicine, 2017.PMID 29072946