The topical application of
delta-aminolevulinic acid (ALA) induces
porphyrin formation in the skin, preferentially in
tumor tissues. Irradiation of the
porphyrin-enriched
tumor tissue with Wood's light leads to emission of a brick-red fluorescence. This principle may be used as a diagnostic procedure which may be termed photodynamic diagnosis (PDD). In ALA-PDD,
tumors and precancerous lesions of the skin reveal a homogeneous, intensive red fluorescence. Psoriatic lesions also show a strong but inhomogeneous
porphyrin fluorescence. ALA-induced
porphyrin fluorescence in preoperative planning is a valuable method to determine the peripheral borders of a given
tumor. The histopathological extensions of the
tumors correlate well with the borders detected by the
tumor-specific fluorescence. The main indications of PDD are the delineation of clinically ill-defined skin
tumors and the control of the efficacy of other
tumor therapies.
Photodynamic therapy (
PDT) utilizes exogenously applied or endogenously formed
photosensitizers and their activation by light to induce cell death via formation of
singlet oxygen and other
free radicals.
PDT is highly efficient in the treatment of solar
keratoses and superficial
basal cell carcinomas. Initial
squamous cell carcinomas also show good response to ALA-
PDT. During the last decade, numerous studies on
PDT for dermatologic diseases were published, the more important ones are reviewed here.