A case of linear porokeratosis treated with photodynamic therapy with confocal microscopy surveillance

Linear porokeratosis (LP) is a rare clinical porokeratosis variant, which typically presents at birth, but can also develop in adulthood. Differential diagnosis includes linear lichen planus, lichen striatus, linear verrucous epidermal nevus, incontinentia pigmenti and linear Darier's disease. An LP lesion has an increased risk of transformation into a squamous cell carcinoma or basal cell carcinoma. The treatment of LP is contradictory and disappointing in general. We present a case of a 16‐year‐old girl with multiple reddish‐brown macules and depressions on the medial aspect of her right arm, localized from the palmar joint up to shoulder region in a linear pattern. We performed confocal microscopy (CLSM) of multiple lesions and a punch biopsy after receiving informed consent to confirm the diagnosis. After diagnosis confirmation, we performed Photodynamic therapy (PDT). Methyl aminolevulinate cream in a 160 mg/g concentration (Metvix crm) was applied under occlusion on the previously cleaned surface of every single lesion for 3 hours. The lesions were subsequently illuminated with a dose of 37 J/cm² (Aktilite, PhotoCure ASA, Norway). Two months after the first PDT treatment, the patient came for a third PDT session. Treatment follow‐up was performed 6 months after the initial PDT session. A CLSM image proved an increase in the width of the stratum spinosum to 42–48 μm, mild post‐inflammatory changes were also present. Cosmetic and clinical response up to date at the time of last follow‐up (1 year) was satisfactory. No progression was observed.