Cross-reactivity patterns of cobalt and nickel studied with repeated open applications (ROATs) to the skin of guinea pigs

Abstract

Background: The relevance of patch-test reactivity to chemicals on cross-challenge is hard to state, but it is generally assumed that the patient might risk a relapse of contact dermatitis when exposed to the cross-reacting compound(s). Objective: To study relevance by using the repeated open application test (ROAT) and applying the inducing allergen cobalt chloride (COCl 2) or nickel sulfate (NiSO 4) as well as the possibly cross-reacting compound (NiSO 4 or COCl 2) topically to guinea pigs. Method: Animals were induced according to the guinea pig maximization test (GPMT) method, patch tested and then treated for 10 days using ROATs. Sensitivity thresholds were determined with serial dilution tests. Results: Guinea pigs induced with COCl 2 reacted in patch testing (100%) and in ROATs to COCl 2 (93%) but not to NiSO 4. Animals induced with NiSO 4 reacted in patch testing to NiSO 4 (100%) but not to COCl 2, and in the ROATs to NiSO 4 (41%) and less to COCl 2. Conclusions: Our results support the assumption that the concomitant patch test reactivity is due to multiple sensitizations rather than cross-reactivity. We previously found that animals induced with palladium chloride (PdCl 2) also reacted to NiSO 4 on patch testing but not in the ROATs, indicating that the results from patch testing might overestimate the risk of a relapse. ROATs in patients with solitary and/or concomitant sensitivity to COCl 2, NiSO 4 or PdCl 2 are desirable.