Real-time LC-OCT monitoring of scalp hypertrophic actinic keratosis clearance following cryotherapy, laser, and 5-fluorouracil therapy.

INTRODUCTION: Assessment of treatment response in hypertrophic actinic keratoses (hAKs) remains largely dependent on clinical examination and dermoscopy, although apparent clearance may not reflect complete resolution of imaging features associated with residual disease. Line-field confocal optical coherence tomography (LC-OCT) enables non-invasive, longitudinal visualization of epidermal, dermal-epidermal junction, and superficial dermal changes at near-cellular resolution. OBJECTIVE: To characterize LC-OCT response patterns in scalp hAKs treated with ablative CO2 laser, cryotherapy, or topical 0.5% 5-fluorouracil/10% salicylic acid, and to evaluate the potential role of LC-OCT in identifying persistent imaging features suggestive of incomplete treatment response requiring retreatment or treatment escalation. METHODS: This retrospective study included 150 scalp hAKs classified at baseline as KIN 2-3 and PRO II-III, allocated to CO2 laser, cryotherapy, or topical 5-FU/SA groups. LC-OCT images acquired during routine follow-up were evaluated at baseline and post-treatment time points for stratum corneum thickness, epidermal thickness, keratinocyte atypia, PRO score, dermal-epidermal junction undulation index, intercellular edema, vascular pattern, and modality-specific structural changes. Treatment response was assessed according to LC-OCT-defined imaging criteria rather than histopathological confirmation. RESULTS: Cryotherapy produced early sub-epidermal blistering, followed by partial imaging response requiring repeated sessions in 40% of lesions. CO2 laser induced immediate epidermal ablation, rapid re-epithelialization, and complete response after retreatment in residual cases, with long-term LC-OCT evidence of dermal collagen remodeling. Topical 5-FU/SA showed heterogeneous responses; 65% of lesions, mainly KIN 3/PRO III, required escalation to a physical modality. CONCLUSION: LC-OCT enables non-invasive monitoring of treatment-related hAKs modifications and may identify persistent imaging abnormalities despite apparent clinical resolution, supporting individualized sequential treatment strategies.