Pretreatment of the test area with 1-day occlusion improves the response rate to NiSO4 5% pet. patch tests in subjects with a positive history of nickel allergy.

A group of 58 women, aged 18 to 51 years, with a clinical history of nickel allergy, who exhibited equivocal or negative reactions to nickel sulfate 5% pet. patch tests performed on the skin of the back, were recruited consecutively from the patch test clinic from September 1993 to June 1994. In order to improve the response rate to NiSO4 5% pet. patch tests, a testing procedure utilizing pretreatment of the test area by 1-day (24-h) occlusion was introduced. Patients underwent 2 patch tests on adjacent sites of the volar surface of both forearms. 3 of the patch tests were performed with 40 mg nickel sulfate 5% pet., whereas a control test was carried out by occluding with an empty chamber. 2 of the nickel sulfate test sites were pretreated with 1-day occlusion performed with an empty chamber. A visual grading system and echographic measurement were used to quantify the responses 30-40 min after patch test removal. Echographic evaluations were carried out using a 20 MHz B-scanner. Measurement of skin thickness and determination of the hypoechogenic dermal area, both considered to be parameters of inflammation, were used to evaluate the intensity of the allergic reaction. At the 3-day (72-h) evaluation, 19 subjects out of 58 clearly showed positive reactions to nickel sulfate 5% pet. at pre-occluded skin sites. Moreover, values of skin thickness and of 0-30 areas at positive pre-occluded nickel test areas were higher in respect to control test areas, confirming clinical evidence of increased response to NiSO4 after occlusion.