Application of thermography to the evaluation of the histamine skin test in man.

The degree of skin flare 10 min after intradermal injection of histamine (0.06-2 micrograms in 0.1 ml saline) was evaluated both visually and by thermography in 6 healthy male volunteers. Intradermally injected histamine increased the skin flare area in a dose-dependent manner. There was a good exponential correlation (r = 0.963) between the flare area evaluated visually and that evaluated by thermography, indicating that the degree of underestimation of the flare area by visual inspection increased with increasing flare size. This could be due to the fact that the rather irregular shape of a flare was rounded by the eyes. Suppressive effects of an antihistamine, terfenadine (20, 40, 60, and 120 mg, p.o.), on the flare caused by histamine (2 micrograms/0.1 ml saline) were evaluated in a similar way in a single-blind, crossover controlled trial using 15 healthy male volunteers. The histamine skin test was evaluated both visually and by thermography before and 4 hr after administration of placebo or each of 4 doses of terfenadine. Terfenadine (20, 40, and 60 mg) suppressed the skin flare in a dose-dependent manner, but 60 and 120 mg had almost the same effect. In all cases the flare area evaluated visually was smaller than that obtained by the thermography, although the degrees of reduction of flare area by the drug were similar by both methods when expressed as a percentage of placebo. In conclusion, thermography could serve as a tool for the objective evaluation of the histamine skin test.