Actinic keratosis — SAQ

Stem

A 68-year-old retired fisherman with a bald scalp and fair skin presents with multiple rough, scaly, erythematous macules on his scalp and forehead. The lesions are easier felt than seen. One lesion on the vertex scalp has become thicker and tender over the past 6 weeks.

Questions

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

b) What is the underlying pathophysiology, and how does this explain the presence of multiple lesions? (2 marks)

c) Outline your management plan for the scalp and facial lesions, including the lesion that has thickened. (3 marks)

^[4]d) What preventive measures and follow-up would you advise? (3 marks)

Model answer

^[4]a) Diagnosis and supporting features (2 marks)

• Actinic keratosis (AK) on a background of field cancerization.
• Supporting features: elderly, fair-skinned, outdoor occupation (fisherman), bald scalp, sun-exposed distribution, rough gritty scaly erythematous macules, easier felt than seen.
• The thickened, tender lesion raises concern for progression to invasive squamous cell carcinoma and requires biopsy.

^[3]b) Pathophysiology and explanation for multiple lesions (2 marks)

• Cumulative UV-induced DNA damage, particularly p53 mutations (UV signature C→T and CC→TT transitions at dipyrimidine sites), in keratinocytes.
• Field cancerization: the surrounding sun-damaged skin contains multiple independent premalignant clones that are not yet clinically visible, explaining why multiple AKs arise in the same field.
• AK sits on a spectrum with SCC in situ (Bowen's disease) and invasive SCC.

^[2]c) Management plan (3 marks)

• Biopsy the thickened tender lesion (shave or punch) to exclude invasive SCC before any destructive treatment.
• Lesion-directed therapy for discrete thin lesions: cryotherapy with liquid nitrogen (5–10 second freeze-thaw) is the gold standard for isolated thin AKs.
• Field-directed therapy for multiple scalp/facial lesions: topical 5-fluorouracil 5% cream once or twice daily for 2–4 weeks; or imiquimod 5% 2–3 times per week for up to 16 weeks; or photodynamic therapy (ALA/MAL with red/blue light) for large fields.
• If biopsy confirms invasive SCC, arrange definitive excision with appropriate margins.

^[1]d) Prevention and follow-up (3 marks)

• Sun protection: broad-spectrum sunscreen, protective clothing, wide-brimmed hat, sun avoidance during peak hours.
• Chemoprevention: nicotinamide 500 mg twice daily reduces new AKs and NMSC in immunocompetent high-risk patients (ONTRAC trial); counsel that it is not effective in transplant recipients.
• Follow-up: dermatology review every 6–12 months for full skin examination and early detection of new AKs or invasive SCC; patient education on self-monitoring and red flags (thickening, bleeding, ulceration).

References4ShowHide

1. [1]Wang JY, Zeitouni N, Austin E, et al. Photodynamic therapy: Clinical applications in dermatology J Am Acad Dermatol, 2026.PMID 39986392
2. [2]Willenbrink TJ, Ruiz ES, Cornejo CM, et al. Field cancerization: Definition, epidemiology, risk factors, and outcomes J Am Acad Dermatol, 2020.PMID 32387665
3. [3]Dianzani C, Conforti C, Giuffrida R, et al. Current therapies for actinic keratosis Int J Dermatol, 2020.PMID 32012240
4. [4]Ferrándiz C, Malvehy J, Guillén C, et al. Precancerous Skin Lesions Actas Dermosifiliogr, 2017.PMID 27658688