Erythema Dyschromicum Perstans Treated With a 1320-nm Nd:YAG Laser: Clinical Response and Histologic Differences Between Treated and Untreated Lesions

Background and Objective: Erythema dyschromicum perstans (EDP) is a chronic pigmentary disorder with limited therapies. The 1320‑nm Nd:YAG laser targets water rather than melanin. We describe a case of EDP treated with this modality, comparing clinical and histopathological features between treated and untreated lesions. Study Design/Patients and Methods: A 26‑year‑old female (Fitzpatrick V) with biopsy‑confirmed EDP received five sessions of Q‑switched 1320‑nm Nd:YAG laser (1.5 J/cm², 1‑cm spot, 5 Hz, 5 passes) on upper extremities with topical therapy. Post‑treatment biopsies were obtained from treated and untreated lesions. Results: Treated extremities showed progressive improvement sustained at 8 and 5.5 months. Lesions treated without topical therapy showed minimal response. Histologically, the treated lesion exhibited mild fibrosis, sparse inflammation, and residual melanophages, whereas the untreated lesion showed active vacuolar degeneration, lichenoid inflammation, and abundant melanophages. Conclusion: Q‑switched 1320‑nm Nd:YAG laser combined with topical therapy may represent a novel treatment for EDP, potentially acting through inflammatory modulation rather than direct pigment clearance. Prospective studies are warranted.