The development and course of test reactions to gold sodium thiosulfate

In our department, gold sodium thiosulfate has become the 2nd most common allergen in routinely patch tested dermatitis patients, with a rate around 10%. Test reactions to this compound often appear late, sometimes so late that active sensitization may be suspected. This study was performed to study the time course of the allergic reaction to gold sodium thiosulfate and to elucidate whether late test reactions mean active sensitization. 10 patients with contact allergy to gold sodium thiosulfate (0.5% pet.) were retested epicutaneously (e.c.) and intracutaneously (i.c.) with dilution series. The clinical course was followed for 2 months with initially short intervals, later more extended. During the entire study, 26 positive e.c. reactions were diagnosed. Within the 1st week, 17 (65%) were recorded. 12 reactions (46% of 26) were noted at the ordinary reading, 3 days after test application. After 10 days, another 9 reactions (35%) appeared. The patients with the latter reactions also had positive test reactions within the 1st week. After 2 months, 9 reactions remained. Out of 30 i.c. tests applied, 25 became positive within 1 week. 19 (76%) of these reactions changed in morphology from thin infiltrates to deep nodules. Another 4 nodules appeared in patients with previous negative i.c. tests. All 23 nodules remained after 2 months. E.c. and i.c. test reactions to gold sodium thiosulfate are long-lasting. Positive patch test reactions emerging after 10 days do not automatically imply active sensitization. To diagnose contact allergy to gold sodium thiosulfate, the ordinary reading at day 3 is insufficient; even reading at 1 week is insufficient and must be supplemented by a reading at 3 weeks. All the i.c. test reactions, however, appeared within 1 week and, in several, a dermal nodule was formed.