Triggering of Koebner Phenomenon by Picosecond Laser in a Psoriatic Patient: Clinical and Immunopathologic Insights.
Teppei Sakai, Koya Sonoda, Jun Omatsu
✦ AI-curated · Sources linked
Case in brief
A 58-year-old woman with well-controlled plaque psoriasis received 755-nm picosecond alexandrite laser treatment for seborrheic keratoses on her back and lower waist. One month later, erythematous, scaly plaques appeared at the irradiated sites; clinical and dermoscopic assessment supported psoriasis, and histology showed psoriasiform changes. Immunohistochemistry found a T-cell-predominant infiltrate, with dermal CD4+ predominance and epidermal CD8+ enrichment. The lesions resolved after 4 weeks of topical corticosteroids and had not recurred by 4 months.
What made this case unusual
The plaques represented Koebner phenomenon after picosecond laser exposure, despite the laser’s minimal thermal damage profile. Coexisting melanocytic nevi did not show the phenomenon.
Diagnostic / clinical pearl
New plaques arising at laser-treated sites in a patient with psoriasis may represent Koebner phenomenon; correlate the clinical pattern with histopathology when the diagnosis is uncertain.
Why it matters
This case supports caution and careful monitoring when picosecond lasers are used in patients with psoriasis, as photomechanical effects may trigger new lesions.