Pain in photodynamic therapy: mechanism of action and management strategies

Abstract

Photodynamic therapy involves administration of a photosensitizing drug and its subsequent activation by irradiation with a light source at wavelengths matching the absorption spectrum of the photosensitizer. In many countries around the world, topical photodynamic therapy has been approved for treatment of cutaneous oncologic conditions such as actinic keratosis, Bowen's disease, and superficial basal cell carcinoma. Multicenter, randomized, controlled studies have confirmed its efficacy and superior cosmetic outcomes compared to conventional therapies. Nevertheless, this therapeutic method presents some adverse effects, such as erythema, edema, pigmentation, pustules, and pain. There is no doubt that pain is the most severe of the adverse effects, being sometimes responsible for definitive treatment interruption. The pain mechanism has not yet been fully understood, which makes complete pain control a challenge to be conquered. In spite of that, this literature review presents some useful pain management strategies as well as the most important pain-related factors in photodynamic therapy. Keywords: Pain, referred; Photochemotherapy; Photosensitizing agents Resumo: A terapia fotodinâmica consiste na administração de uma droga fotossensibilizante e sua subseqüente irradiação com uma fonte de luz de espectro correspondente ao do seu fotossensibilizador. Em diversos países do mundo, a terapia fotodinâmica tópica é aprovada para o tratamento de condições oncológicas cutâneas como queratoses actínicas, doença de Bowen e carcinoma basocelular superficial. Estudos multicêntricos controlados e randomizados confirmam sua eficácia e seus resultados cosméticos superiores em relação às terapias convencionais. No entanto, existem alguns efeitos adversos inerentes a esse método terapêutico, como eritema, edema, pigmentação, pústulas e dor. Essa última é, sem dúvida, a mais importante deles, chegando a ser responsável pela interrupção definitiva do tratamento em alguns casos. O mecanismo dessa dor permanece ainda não completamente entendido. Tal fato faz do controle total da dor durante a terapia fotodinâmica um desafio ainda a ser conquistado. Apesar disso, esta revisão apresenta algumas estratégias que podem ajudar os pacientes a tolerar melhor a terapia fotodinâmica, além de relacionar os principais fatores ligados à dor descritos na literatura.

Current evidence and applications of photodynamic therapy in dermatology

“…It has the advantage of allowing application to multiple lesions. Pain, edema, erythema, pigmentation, and pustules are among the main complications, with the most common complaint being pain during delivery of treatment 4,5. In this paper, we review the evidence for current applications of PDT in dermatology.…”

Photodynamic Therapy for Malignant Skin Lesions

“…However, one therapy that has not proven effi cacious is topical anesthetics in PDT. It is postulated that since both ALA and MAL have an acidic pH and the majority of the topical anesthetics have an alkaline pH, their combined use is incompatible (Chaves et al 2012 ).…”

Three-dimensional illumination procedure for photodynamic therapy of dermatology

“…Pain level increases with irradiance; however, the exact pain mechanism remains unclear. 10 Significant advances in light dosimetry studies of PDT have been obtained for in vivo propagation models, which correlate incident irradiance and physiological outcomes in biological materials. 11,12 However, light dosimetry is hardly controllable in vivo because of irregularly shaped lesions, segmentation difficulty in normal areas, the patient's movement during the treatment, and so on.…”