OSCE — safe cutaneous cryotherapy: indications, technique, freeze times, and complications

Brief (to candidate)

A 55-year-old outdoor worker has multiple facial actinic keratoses and a separate common wart on the hand. He asks for “freezing treatment today.” He has darker skin phototype and a history of cold-induced whitening of fingers. You have 8 minutes to select appropriate lesions, explain technique and risks, and plan freeze parameters.

Candidate instructions

1. State indications (AK, warts, seborrhoeic keratosis, selected benign lesions) and when not to freeze.
2. Describe liquid nitrogen technique (spray/probe, freeze–thaw cycles).
3. Give approximate freeze times by lesion type.
4. Counsel expected sequelae (blister, hypopigmentation) and complications.
5. Identify contraindications/cautions (uncertain diagnosis, melanoma suspicion, cold injury risk).

Examiner checklist (mark each domain / 10)

Model key actions

• Freeze only lesions with confident benign/AK diagnosis; biopsy first if doubt.^[1][4]
• Use LN2 freeze–thaw with margin ice-ball; match freeze intensity to lesion (AK vs wart).^[2][3]
• Counsel blister and pigment change; caution in dark phototypes and cold-sensitive patients.^[9]

Common errors

• Freezing a pigmented lesion of uncertain diagnosis.
• Using cryotherapy as definitive therapy for high-risk skin cancer without oncology pathway.
• No warning about permanent hypopigmentation.
• Over-freezing digits/periungual without nerve risk discussion.
• Treating Raynaud-severe patient without caution.