20 | WHERE THE SUN DOESN'T SHINE, UV FLUORESCENCE DOES: DIAGNOSTIC AND THERAPEUTIC INSIGHTS OF UV-INDUCED FLUORESCENCE DERMOSCOPY IN SCROTAL POROKERATOSIS

Z. Fratton^1|2, M. Milani³, D. Strippoli⁴, A. Ponziani⁴, F. Fantini⁴, M. Andreassi⁴ | ¹Department of Medicine, Institute of Dermatology, University of Udine, Italy; ²Dermatology Unit, Ospedale San Bortolo, Vicenza, Italy; ³Department of Pathology, ASST Lecco, Alessandro Manzoni Hospital, Lecco, Italy; ⁴Dermatology Unit, ASST Lecco, Alessandro Manzoni Hospital, Lecco, Italy

Background. Porokeratosis is a clonal disorder of keratinization histologically characterized by the presence of cornoid lamella, a parakeratotic column overlying a small vertical zone of dyskeratotic and vacuolated cells within the epidermis. Scrotal involvement is rare and often presents a diagnostic challenge due to its subtle clinical appearance and potential overlap with other genital inflammatory and infectious conditions.
Case Presentation. A 62-year-old male presented with a several-month history of mildly pruritic, 1-cm annular lesions on the scrotum. Polarized light dermoscopy failed to clearly identify a peripheral keratotic border. However, 365 nm UV-induced fluorescence dermoscopy (UVFD) revealed a distinct cornoid lamella, appearing as a "double-track" sign. Notably, the lesions exhibited a bright pink fluorescence, suggestive of a Corynebacterium superinfection (protoporphyrin production). Initial histological examination reported "skin with hyperorthokeratosis and hyperparakeratosis, elongation of dermal papillae, consistent with post-inflammatory outcomes." Guided by the UVFD findings, a slide review was requested, which successfully identified the diagnostic parakeratotic column (cornoid lamella). The patient was managed with local disinfection and moisture control. At the one-month follow-up, the pruritus had completely resolved. Re-evaluation with UVFD confirmed the disappearance of the pink fluorescence, while the coronoid lamella remained visible. These findings suggest a link between the Corynebacterium infection and the pruritic symptoms.
Conclusions. This case highlights the rarity of scrotal porokeratosis and the innovative role of UV-induced fluorescence dermoscopy as a crucial diagnostic aid. The unexpected finding of pink fluorescence not only facilitated the diagnosis by enhancing the visualization of the cornoid lamella but also provided a rationale for the pruritic symptoms, which can cause severe discomfort in patients with scrotal porokeratosis. UV-induced fluorescence dermoscopy represents a valuable second-level tool to improve diagnostic accuracy and guide the pathologist in cases where standard dermoscopy and initial histology are inconclusive. Furthermore, UVFD can guide therapeutic choices, especially in cases where irritant topicals (e.g. tacalcitol, tacrolimus, topical retinoids) or physical modalities (e.g. cryotherapy) are less advisable.