Punch biopsy technique

Indications

• Inflammatory dermatoses: eczema, psoriasis, lichen planus, lupus erythematosus.
• Autoimmune blistering: bullous pemphigoid (lesional + perilesional for DIF).
• Granulomatous: sarcoidosis, granuloma annulare, necrobiosis lipoidica.
• Cutaneous lymphoma — multiple sites for diagnostic yield.
• Vasculitis.
• Connective tissue disease (morphoea, scleroderma, dermatomyositis).
• Small to medium tumours (BCC, melanocytic naevus, neurofibroma) — diagnostic only.
• Suspected pigmented lesions if clear margin assessment not required (full excision generally preferred for suspected melanoma; refer below).
• Mucosal biopsies (oral, genital).

Technique

1. Pre-procedure: explain, consent, mark site / orientation, photograph.
2. Local anaesthesia: lidocaine 1-2% ± adrenaline (avoid in digital end-arteries unless using established adrenaline-safe protocol).
3. Antiseptic prep: chlorhexidine 0.5-2% or povidone-iodine; sterile drape.
4. Select trephine size:
   • 2-3 mm: diagnostic biopsy where minimal scarring required.
   • 4 mm: standard inflammatory / tumour diagnostic.
   • 5-6 mm: larger lesions, deeper tumours, where adequate dermis needed.
   • 8 mm: deeper biopsy (subcutaneous panniculitis, dense infiltrates).
5. Skin tension: stretch skin perpendicular to RSTL → final wound becomes oval.
6. Rotation: hold trephine perpendicular to skin; rotate with downward pressure through full epidermis + dermis until subcutaneous fat is reached.
7. Lift gently with fine-tooth forceps or skin hook; avoid crushing.
8. Cut base with iris scissors at subcutaneous level.
9. Place in fixative: 10% buffered formalin for routine; Michel medium / saline for DIF; PBS / fresh for molecular / electron microscopy.
10. Closure:
    • Small punches: secondary intention or simple primary closure.
    • Intermediate punches: simple interrupted closure where needed.
    • Larger punches: layered closure where depth or tension requires it.

Pitfalls and limitations

• Inadequate depth in panniculitis (need deep wedge or excisional rather than punch).
• Crush artefact with rough handling — distorts pathology.
• Pigmented lesions: punch biopsy may sample a non-representative area; complete excisional biopsy preferred for suspected melanoma (NICE NG14).
• Lower-leg / shin biopsies: high risk of poor healing; counsel.
• Bleeding risk: appropriate haemostasis (ferric sulphate, electrocautery).
• Wrong site: photograph and mark; specimen-mapping for multiple biopsies.
• Inadequate IHC: send for indicated specialist markers (e.g. TCR rearrangement for CTCL).

Aftercare

• If sutures used, typically removed at 7-14 days depending on site.
• Emollient use when dressings no longer required; sun protection.
• Counsel about scar formation; photograph at follow-up.
• Communicate biopsy result via timely pathway (2-week-wait or routine).