The purpuric patch test in patients with allergic contact dermatitis from azo dyes

The histopathological features of the purpuric patch test have been describ ed in individual cases only. We report a series of patients with allergic c ontact dermatitis, who developed purpuric patch tests at the sites of aller gens from the azo dye group. 105 patients were clinically evaluated and tes ted with the TRUE Test and the textile color & finish series (Chemotechniqu e Diagnostics) because of suspected clothing dermatitis. Positive results t o the latter were found in 31 patients (29.5%). In 9 of these, purpuric pat ch tests were observed at the sites of the allergens Disperse Blue 124, 106 and 85. 10 biopsies were performed and studied. The histopathological chan ges of the purpuric patch test included: spongiosis (in 90% of cases), exoc ytosis (70%), and dilated blood vessels (100%) without signs of vasculitis, surrounded by an inflammatory infiltrate composed mainly of T lymphocytes. Extravasated erythrocytes were seen perivascularly, but also in the inters titium, surrounding the acrosyringium, at the dermoepidermal junction, and in the epidermis. Increased number of mast cells were found in 22.2% of cas es. Disperse Blue 124, 106, and 85 are potent allergens that can elicit pur puric patch test reactions. The purpuric patch test in our cases was a mani festation of an allergic reaction, based not only on histopathological chan ges, but also on evolution and relevance of the patch tests.