Photodynamic Therapy: Protocol and Indications

Overview / Definition Photodynamic therapy (PDT) is a treatment that combines a photosensitizing agent with light exposure to selectively destroy abnormal cells. The photosensitizer is absorbed by the target tissue, and upon activation by a specific wavelength of light, it generates reactive oxygen species (ROS) that lead to cellular apoptosis and necrosis. Epidemiology PDT is increasingly being recognized as a valuable treatment option in dermatology due to its effectiveness in managing various skin conditions. Common indications include: Non-melanoma skin cancers (e.g., basal cell carcinoma, squamous cell carcinoma) Actinic keratosis Psoriasis Acne vulgaris Viral warts Pathophysiology / Mechanism The mechanism of PDT involves: Absorption of light by the photosensitizer, which is preferentially taken up by diseased cells. Activation of the photosensitizer with a specific wavelength of light (usually red light). Generation of ROS, leading to oxidative stress, mitochondrial dysfunction, and subsequent cell death. This process not only destroys the targeted cells but also induces a local inflammatory response that can enhance the clearance of remaining abnormal cells. Clinical Presentation Patients undergoing PDT may present with a variety of conditions, including: Actinic keratosis: Scaly patches on sun-exposed skin. Basal cell carcinoma: Pearly nodules or non-healing ulcers. Psoriasis: Red, scaly plaques. Acne vulgaris: Inflamed papules and pustules. Diagnosis / Workup The diagnosis of conditions suitable for PDT often involves: Clinical examination: Visual assessment of lesions. Biopsy: May be necessary to confirm malignancy for basal cell carcinoma or squamous cell carcinoma. Histopathology: Examination of tissue samples to evaluate for dysplastic changes. Imaging studies are typically not required for superficial skin lesions. Treatment / Management PDT is performed in several steps: Preparation: Cleanse the skin and remove any debris. Application of photosensiti