A sequential histopathological study of dermographism

Wheals were induced in four dermographic patients using a dermographometer applying a standard pressure (7·2 × 10⁵ Pa). Biopsies were taken from control, normal, non-whealed skin and from the induced wheals at 5 min, 15 min, 2 h and 24 h. Two further dermographic patients were biopsied 2 h after induction of wheals induced by two different pressures (2·5 and 10·9× 10⁵ Pa). Additional control skin biopsies were taken from eight non-dermographic individuals. The histological changes were only seen in the upper dermis. In non-traumatized skin there was a significantly raised mononuclear cell count (15·6±SE 2·3 compared with 8·1±0·6 in non-dermographic controls; P= 0·0002). In whealed skin there was some cndothelial cell swelling seen at 5 min which persisted at 24 h. The mononuclear cell infiltrate did not change quantitatively throughout the observation period; neutrophils were seen at 5 min, reached a peak at 2 h and were still present at 24 h; there was, however, a great inter-patient variation in the degree of neutrophil infiltration. Mast cell numbers did not change significantly and were numerically similar to those found in non-dermographic individuals. There appeared to be no qualitative or quantitative difference in the infiltrate in the wheals induced by the two different pressures. Immunofluorescence studies were negative in all the biopsies.