Cryotherapy (cryosurgery) — SAQ

Stem

A 28-year-old man presents to his general practitioner with a painful, firm, hyperkeratotic papule on the sole of his right foot that has been present for eight months and is interfering with walking. He has tried over-the-counter salicylic acid paint intermittently with no improvement. On examination there is a 7 mm verrucous nodule on the plantar surface with disruption of the skin lines and several black pinpoint dots within it. The GP proposes treatment with liquid nitrogen cryotherapy.

Questions

a) What is the most likely diagnosis and what clinical features support it? (2 marks)

b) Outline the mechanism by which liquid nitrogen destroys tissue. (3 marks)

^[1][4]c) Describe the correct cryotherapy technique for this lesion, including freeze time, number of cycles, ice-ball halo, and session interval. (3 marks)

d) What are the key complications and the aftercare advice you would give? (2 marks)

Model answer

a) Diagnosis (2 marks) — Plantar viral wart (common wart, verruca plantaris), caused by human papillomavirus (HPV) infection. Supporting features: firm hyperkeratotic verrucous nodule on the sole, disrupted skin lines, black thrombosed capillary dots within the lesion, pain on walking, and failure of intermittent salicylic acid.^[1]

^[1][3]b) Mechanism (3 marks) — Liquid nitrogen boils at -196 C; the lethal target temperature is approximately -20 to -30 C. Four mechanisms converge to kill the target cells: (1) extracellular ice formation raises extracellular osmolarity and draws water out of the cell, producing dehydration and solute-effect injury; (2) intracellular ice forms with rapid freezing and mechanically disrupts the cell membrane — the most lethal mechanism; (3) vascular stasis injures the microvasculature, producing thrombosis and ischaemic infarction; (4) apoptosis occurs at the sub-lethal periphery. A slow thaw allows ice-crystal recrystallisation that magnifies injury, and a second freeze-thaw cycle widens the zone of complete necrosis.

^[2]c) Technique (3 marks) — Pare the hyperkeratotic callus first so the lethal isotherm reaches the deeper wart tissue. Apply liquid nitrogen by open spray until a uniform ice ball extends 2-3 mm beyond the visible margin. Allow complete thaw to body temperature; this is one cycle. Use two cycles of 10-15 seconds each per session. Repeat sessions every 3-4 weeks for up to three or four sessions; combine with salicylic acid between sessions. Expected clearance is 50-70% after a course, with a 20-30% recurrence rate.

^[1]d) Complications and aftercare (2 marks) — Immediate: pain, erythema, oedema. Early (24-48 h): blister formation (may be haemorrhagic, expected — indicates adequate freeze depth; do not deroof, aspirate with a sterile needle if large and painful). Late: permanent hypopigmentation (melanocytes are more cold-sensitive than keratinocytes — the most important long-term complication), transient hyperpigmentation, scarring, recurrence. Aftercare: wash normally; apply white soft paraffin (Vaseline) if crusted; leave the blister intact; sun protection; return if spreading, recurrent, or darkening.

References4ShowHide

1. [1]Chanal J, Aubin F, Penso-Assathiany D, et al. A multicentre pragmatic randomized controlled trial comparing 50% salicylic acid, liquid nitrogen, 5% 5-fluorouracil cream, and 5% imiquimod cream in previously treated plantar warts. The VRAIE (VeRrues plAntaIres en villE) study Ann Dermatol Venereol, 2025.PMID 40743833
2. [2]Chanal J, Aubin F, Penso-Assathiany D, et al. A multicentre pragmatic randomized controlled trial comparing 50% salicylic acid, liquid nitrogen, 5% 5-fluorouracil cream, and 5% imiquimod cream in previously treated plantar warts. The VRAIE (VeRrues plAntaIres en villE) study Ann Dermatol Venereol, 2025.PMID 40743833
3. [3]Chanal J, Aubin F, Penso-Assathiany D, et al. A multicentre pragmatic randomized controlled trial comparing 50% salicylic acid, liquid nitrogen, 5% 5-fluorouracil cream, and 5% imiquimod cream in previously treated plantar warts. The VRAIE (VeRrues plAntaIres en villE) study Ann Dermatol Venereol, 2025.PMID 40743833
4. [4]Chanal J, Aubin F, Penso-Assathiany D, et al. A multicentre pragmatic randomized controlled trial comparing 50% salicylic acid, liquid nitrogen, 5% 5-fluorouracil cream, and 5% imiquimod cream in previously treated plantar warts. The VRAIE (VeRrues plAntaIres en villE) study Ann Dermatol Venereol, 2025.PMID 40743833