D3.97 - Allergic contact dermatitis confirmed by repeated open application test in a 68‑year‑old patient

Background

We present a case of allergic contact dermatitis (ACD) induced by a topical composite preparation containing titanium dioxide complex, kaolin, and hyaluronic acid. A repeated open application test (ROAT) allowed confirmation of the causative agent and demonstrated its clinical relevance.

Methods

A 68‑year-old female presented with a 4‑month history of an erythematous plaque on the dorsum of the right foot. She had no personal or family history of atopy. Seven months prior, she sustained a burn on the same site, treated with composite preparation. Three months later, an erythematous plaque developed, associated with pruritus. She was treated several times with systemic antibiotics, as the lesion was initially interpreted as a secondary bacterial infection, and applied topical products containing fusidic acid cream, thirotricin gel, antiseptic solution containing octenidine dihydrochloride and phenoxyethanol, and composite preparation. She was prescribed a mid-potency corticosteroid cream and a systemic second-generation antihistamine, taken twice daily, and instructed to perform the ROAT at home. ROAT was performed on the inner side of the forearm by applying each topical product twice daily for 7 consecutive days. The patient continued antihistamine therapy during the test. A subsequent ROAT after cessation of antihistamines and a washout period had been planned, but the positive result made it unnecessary. Written informed consent was obtained from the patient for publication of clinical details and images.

Results

After 2 days, a clearly demarcated erythematous reaction associated with pruritus developed exclusively at the site of the composite preparation containing titanium dioxide complex, kaolin, and hyaluronic acid, confirming ACD, while no reactions occurred at other sites. Discontinuation of the offending preparation and topical corticosteroid therapy under occlusion led to near-complete resolution within 2 weeks.

Conclusions

This case illustrates that ROAT can reliably identify clinically relevant allergens in ACD. The positive reaction occurred despite ongoing antihistamine therapy, demonstrating that ROAT may serve as a practical tool in real-world settings to confirm the causative agent and guide avoidance, even if not formally recommended.