الفهرس 
History of PDTOnly 14 pages are availabe for public view
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Abstract
The use of sunlight for the treatment of various skin disorders (heliotherapy) was known to ancient Indians and Greeks. In the modern era, Oscar Raab, a German medical student first reported the death of Paramecium caudatum (a protozoan) after light exposure in the presence of acridine orange in the year 1900. His professor, von Tappeiner, coined the term ”photodynamic” to describe oxygen-consuming chemical reactions in vivo . Von Tappeiner and Jesionek (a dermatologist), in 1904, used topical eosin and visible light to treat skin tumors, condyloma lata and lupus vulgaris.
PDT is a treatment modality involving administration of a photosensitizing compound, accumulation of the sensitizer molecules in the target cells followed by selective irradiation of the lesion with visible light. The drug and light are individually non-toxic, but in combination destroy tissues. The efficacy of PDT depends on all the following mechanisms which are inter-linked: direct cytotoxicity, vascular damage, inflammation and immune host response
An ideal photosensitizer should be chemically pure, have capability of localizing specifically in neoplastic tissue, should accumulate maximally in tumor in short time, and have a short half-life and rapid clearance from normal tissues. It should activate at wavelengths with optimal tissue penetration, have a high quantum yield for singlet oxygen generation, should lack dark toxicity and should be effective on topical application for dermatological uses.
Initially, after systemic administration, photosensitizing compounds are taken up by most normal and malignant cells, but are retained longer in tumor and rapidly proliferating cells. The drug is activated by light corresponding to the absorption spectrum of the compound.
Hematoporphyrin derivative was the first systemically studied photosensitizer for clinical PDT.
Topical PDT depends on protoporphyrin IX (PpIX) formed endogenously in tissue after application of d-aminolevulinic acid (d-ALA). Topical application of d-ALA subverts the negative feedback effect on the heme pathway and leads to accumulation of endogenous PpIX in significant levels. ALA-PDT was first used for various malignant skin lesions. The main advantage of topical ALA-PDT is the absence of generalized photosensitivity.
Light sources that have been developed specifically for PDT include: Commercially available lamps with appropriate red light emission for large surface areas- metal halogen lamp (600-800 nm high power density)
and Short arc xenon lamp (400-1200nm).
PDT is now a well established treatment option for actinic keratosis, basal cell carcinoma, and Bowen disease. In psoriasis of the chronic plaque type, both systemic and topical PDT have shown results, in some cases equivalent to results with dithranol. Though no controlled studies have been done, topical PDT showed clearing of chronic plaque psoriasis,Verrucae vulgaris, including recalcitrant ones, laryngeal papillomas and condyloma acuminata. PDT has also been used for the treatment of recalcitrant and HIV-associated molluscum contagiosum.. PDT appears to be an efficient modality for cutaneous vascular malformations with excellent cosmetic results. Although it should be noted that there are a number of other therapeutic options for these disorders, PDT constitutes an important addition to the range of possible therapies and should be made available whenever it is considered the best treatment option. Its superior cosmetic results compared with other treatment modalities have been demonstrated………
There are several important reasons why PDT has not yet been accepted as a standard treatment method despite the extensive clinical experience that has been accumulated since the late 1970s and these include, burning pain, stinging or itching restricted to the illuminated area may be seen during light exposure. Erythema and edema of the treated area may occur after light exposure. There is crusting, scaling accompanied by pruritus and then healing takes place by 2 to 8 weeks. Photophobia and ocular discomfort may also occur.
However, the merits of PDT outweigh by far its demerits in most cases and it is going to be an important part of the dermatologists’ armamentarium in the future. For better therapeutic efficacy with PDT more clinical, biochemical and physical research will be needed.