Echographic evaluation with image analysis of histamine-induced wheals

10 healthy, non-atopic women, aged 20-30, underwent histamine prick tests, performed in duplicate on the volar surface of the forearm with progressively increasing histamine concentration, from elbow to wrist on the left arm and from wrist to elbow on the right. Histamine wheal assessments were performed with the following methods at 5, 10, 15 and 20 min from challenge: planimetry for wheal area determination, A-scanning for skin thickness evaluation and echographic image analysis for assessing skin edema corresponding to the hypoechogenic area in the dermis. Wheal extension, skin thickness and edema of the dermis increase in time according to the histamine concentration. However, in response to the same concentration, regional variations consisting in greater wheal extension and dermis hypoechogenic areas were observed on proximal than on distal sites. Conversely, statistically significant differences were found between tests carried out on the right arm compared to those on the left regarding skin thickness. These variations have to be considered when interpreting data derived from pharmacological studies on the inhibition of histamine-induced reactions.