Telethermography: an objective method for evaluating patch test reactions

Telethermography (TT) is a non-invasive imaging technique which can be used to evaluate the body's thermal gradients. It has recently been used as a diagnostic tool in many medical fields, especially in the study of the skin and other external organs. We assessed the applicability of TT in the objective evaluation of patch tests in allergic contact dermatitis, where clinical assessment is difficult, especially for atopic or brown-skinned individuals. In 34 individuals with a history of allergy to nickel sulphate (NiSO4), we applied a patch containing NiSO4 to the right side of the back and a patch containing 1% sodium-lauryl-sulphate (SLS) to the left side. As a control, we applied a patch containing an irritant (1% SLS) in a second group of 30 non-allergic individuals. A peculiar pattern was found for allergic reactions. This was characterized by a hot area that extended beyond the borders of the patch site and was oriented towards the nearest lymph-node(s), spreading as a hyperthermic line or lines. For the irritant test (SLS), the hot area was limited to the patch area, and the thermal gradients were lower. Thermography can be considered a useful complementary method for the evaluation of patch tests.