DETECTION OF DYSPLASTIC LESIONS BY FLUORESCENCE IN A MODEL OF COLITISIN RATS AFTER PREVIOUS PHOTOSENSITIZATION WITH 5-AMINOLEVULINIC ACID

Background and Study Aims: Endoscopic diagnosis of dysplastic lesions and early cancers in chronic ulcerative colitis is a major problem, Id entification of suspicious lesions is influenced by the macroscopic ap pearance of the colon, but also by the endoscopist's experience. In th is study we evaluated the identification of dysplastic lesions by the naked eye in an animal model of colitis after 5-aminoaevulinic acid-in duced photosensitization. Methods: 80 male Wistar rats were examined, Acute and cronic colitis were induced by oral application of 5 % dextr ane sulfate sodium (DSS) in 1-7 cycles (1 cycle = seven days DSS and 1 0 days water). For sensitisation 5-aminolaevulinic acid (5-ALA) at dif ferent doses (0, 10, 25, 50, 75, 100, and 200 mg/kg) was used. The col onic fluorescence was examined under a blue light (390-436 nm) for exc itation. Histological findings of fluorescent and non-fluorescent biop sy specimens were recorded. Results: Using 100 mg/kg 5-ALA intravenous ly for photosensitization, all dysplastic lesions (5/5) showed fluores cence (sensivitity 100 %), However, at this concentration of 5-ALA, 60 false positive lesions were found out of 76 specimens taken from lesi ons that were not dysplastic - only 16 specimens of non-dysplastic les ions did not fluoresce (specifity 21 %), Using 75 and 50 mg/kg 5-ALA i ntravenously sensitivity decreased to 92 % (36/39) and 42% (5/12), res pectively, while specificity increased to 35 % (29/82) and 62 % (45/73 ), Using 50 mg/kg 5-ALA intravenously, fluorescence-positive biopsy sp ecimens showed inflammation of the colon in 31 % whereas only 12 % con tained normal mucosa (p < 0.01). The distribution of fluorescence-posi tive biopsy specimens with histologically confirmed inflammation was s imilar for different grades of inflammation after sensitisation with 7 5 and 100 mg/kg 5-ALA, whereas with 50 mg/kg 5-ALA fluorescence-positi ve biopsy specimens contained significantly (p < 0.05) more moderate, massive, or ulcerative inflammation (79 %) than mild inflammation (21 %). Conclusion: 5-ALA induced photosensitization gave a high sensitivi ty, but low specificity in identifying dysplastic lesions in DSS-induc ed colitis in rats. In this animal model inflammation is a major facto r in disturbing the fluorescence localisation of dysplasia after sensi tisation with 5-ALA.