CD27 Indium contact allergy: the only positive case identified at a tertiary centre

Abstract

A 23-year-old woman with atopic dermatitis presented with recurrent periorbital dermatitis, with intermittent involvement of the hands and flexural areas. She reported cutaneous reactions following metal contact, including stainless-steel bowls and cutlery at work as a chef, and avoided jewellery due to previous skin flares. Her history was notable for perioral dermatitis during orthodontic treatment with metal braces, which improved following removal. Initial patch testing, including standard, cosmetics, fragrances, acrylates and metal series, was negative at day 4. Delayed reactions were reported by the patient on day 12, with positive reactions to indium chloride and indium sulfate confirmed by repeat patch testing to selected metals. However, on her second patch test, beryllium sulfate tetrahydrate, gold sodium thiosulfate and manganese chloride were additionally positive. Dental materials were considered a potential source of exposure and sensitization. Indium is a rare post-transition metal with high ductility and corrosion resistance, used in electronic components, displays, dental alloys, jewellery, temperature sensors and nuclear medicine. It was introduced into the Chemotechnique Diagnostics metal series in 2008 and may be tested as elemental indium (10% aqueous) or as salts, including indium chloride (1% petrolatum) and indium sulfate (10% aqueous). Since its inclusion in the metal series in 2008, 659 patients at our centre have undergone patch testing to indium; this represents the only positive case identified, highlighting the extreme rarity of indium as a contact sensitizer. Published reports of indium sensitization are limited to isolated case reports and small series, with exposure linked to jewellery, dental alloys and occupational settings, including electronics manufacture and laboratory work. Indium is an extremely rare but clinically relevant contact allergen. Clinicians should consider targeted testing for uncommon metals in patients with metal-associated dermatitis. Extended readings beyond day 4, as well as repeat patch testing, may be required to identify these rare sensitizers.