Cutaneous reactivity to allergens at 24‐h increases from the antecubital fossa to the wrist: an echographic evaluation by means of a new image analysis system

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Abstract
To establish the existence of regional variations in response to allergens, we performed patch tests with nickel sulfate 5% pet. at 4 different sites on the volar forearm skin in 17 nickel-sensitive women, aged from 18 to 45 years. After a 24-h application, patch tests were removed and evaluated both by clinical scoring and by means of a 20 MHz ultrasound B scanner. Recorded echographic images referring to uninvolved skin and to positive test sites were evaluated by a traditional image analysis method for the determination of skin thickness. Furthermore, they were processed by software which ascribes arbitrary values to the amplitude levels of the echoes and enables quantification of the pixels, (the smallest elements in a visual display with controllable colour and brightness) forming objects reflecting within a selected amplitude band. Thus, we demonstrated an increase in thickness of uninvolved skin at distal sites and a greater reactivity at 24 h to patch tests in skin areas near to the wrist crease, as evidenced by a greater increase in pixel and in thickness values at distal sites. From our data, we have a clear indication for the use of rotating patterns or symmetrical sites in quantitative and comparative investigations concerning the evaluation of contact allergy on volar forearm skin.