Intralesional ALA-PDT for residual extramammary Paget's disease: a case report

Extramammary Paget's disease (EMPD) is a rare cutaneous malignancy often associated with positive surgical margins and high local recurrence rates. While wide local excision remains the standard treatment, re-excision may be impractical in anatomically sensitive areas. Topical photodynamic therapy (PDT) is frequently used for superficial lesions but its efficacy is limited by poor photosensitizer penetration, particularly when tumor cells invade deep into the dermis or adnexal structures.

An elderly male with scrotal EMPD underwent surgical excision, but postoperative pathology revealed positive margins with tumor infiltration into the subcutaneous fat. Further wide excision was deemed unfeasible due to functional and anatomical constraints. Pre-treatment high-frequency ultrasound demonstrated a lesion thickness of approximately 2.7 mm, exceeding the effective penetration depth of topical PDT. To overcome this barrier, intralesional 5-aminolevulinic acid photodynamic therapy (ALA-PDT) was administered monthly. A 10% ALA solution was injected directly into the residual plaque, followed by a 2-hour incubation and irradiation with 630 nm red light at a fluence of 120 J/cm². After three sessions, the indurated erythematous plaque showed marked thinning and fading; complete clinical regression was achieved after six sessions. The treatment was well-tolerated, with only mild pain and transient erythema. No recurrence was observed during the 6-month follow-up period.

Intralesional ALA-PDT is a highly effective, minimally invasive, and tissue-preserving treatment for residual EMPD with deep dermal invasion. By ensuring adequate photosensitizer delivery throughout the entire lesion, it overcomes the penetration limitations of topical PDT and represents a valuable option when surgery is not feasible.