Occupational allergic contact dermatitis due to cobalt from a metal nut

Cobalt is a shiny silvery metal known for its hardness, wear-resistance and ability to create hard metal.1, 2 The prevalence of allergic contact dermatitis to cobalt is 1%–4% among the general population and 4%–11% among dermatitis patients.1 Several occupational groups, such as healthcare workers, electronics, construction and hard metal industry workers, are especially exposed and affected.1, 3 We present a rare case of occupational allergic contact dermatitis to cobalt due to direct skin exposure to a metal nut. A 34-year-old man was seen in our department on suspicion of occupational hand dermatitis. He had no history of skin or allergic disease. The patient had been working in a car repair workshop for 2 years before the debut of vesicular dermatitis in the interdigital area and palms of both hands (Figure 1A). During the following months, the patient's dermatitis was continuously aggravated, affecting the dorsal side of hands, wrists and distal part of forearms, with significant improvement during weekends and holidays. The patient's primary working tasks were to handle tools, metal spare parts, cut, engine and gear oil, brake fluid and windshield washer fluid. His hands were exposed daily to rubber gloves, 5–10 hand washes and 15–20 hand disinfections. There were no domestic or leisure time exposures of relevance. Patch testing was performed on the patient's upper back with allergens from Chemotechnique MB Diagnostics AB (Vellinge, Sweden) and SmartPractice allergEAZE® (Hillerød, Denmark) in Finn Chambers® (8 mm; SmartPractice®, Phoenix, AZ, USA), occluded for 48 h with Norgesplaster® AS Scanpor tape (Vennesla, Norway). The patient was patch tested with the European Baseline Series, relevant extended patch test series and the patient's working gloves. Readings were performed on Day 2 (D2), D3 and D7, according to ESCD guidelines.4 There was a strong positive reaction (2+ reactions on D4 and D7) to cobalt chloride 1% in pet. (CAS.nr: 7440-48-4). A handheld x-ray fluorescent (XRF) device (X-MET8000 Series, Uedem, Germany) was used to detect cobalt in 21 of 24 suspected metal auto items (range: 100–2200 ppm). The five metal items with the highest cobalt content were then tested for cobalt release with the Nitroso-R-spot test. One metal nut (Figure 1C) spot tested positive (Figure 1B). The patient was diagnosed with allergic contact dermatitis due to occupational exposure to cobalt from a metal nut. He was instructed to avoid direct skin contact with cobalt by use of gloves, and to treat his hand dermatitis with topical corticosteroids. The patient was treated with success, and his symptoms were further reduced during a 3-week summer vacation. Cobalt is the second most common metal contact allergen after nickel.3 Cobalt is a strong sensitiser with a ED10 level of 0.07–1.95 μg/cm2, corresponding to 30.8–259 ppm.5 The culprit metal nut in this case study was measured at 1800 ppm. Thus, significantly higher than the ED10 level for cobalt. Still, there are no regulatory limits for the release of cobalt from metal objects.6, 7 The causative exposure to cobalt is rarely found.2, 3 Previous similar case reports have found clinically relevant exposure through polyester resin,8 and machine oil.7 Other important known sources of skin exposure to cobalt are jewelry2, 6 and beauty tools9 and leather.10 We detected cobalt with XRF in the majority of the mechanical metal items collected from the patient's workplace. The culprit item—a metal nut (Figure 1C)—was identified by the use of the colourimetric Nitroso-R-spot test (Figure 1B). The XRF and spot test are quick, non-invasive and affordable methods that can be useful in detecting cobalt in clinically suspected metal items.2, 6, 11 The presence of a yellow or red colour change in the swab indicates a positive result, while no change in colour signifies a negative result.6, 11 However, it might be difficult to interpret the colourimetric Nitroso-R-spot test, and concerns have been raised regarding the sensitivity and specificity of the test.6, 11, 12 Furthermore, we might not have detected all culprit metal objects from the patient's workplace, and there might be an additional irritant component to the patient's interdigital eczema. In conclusion, in case of clinical suspicion of allergic contact dermatitis to cobalt due to metal items, the XRF and Nitroso-R-spot testing can be useful as diagnostic measurement tools. Sofia Botvid: Conceptualization; investigation; methodology; writing – original draft; writing – review and editing. Ulrik Ahrensbøll-Friis: Investigation; methodology; writing – review and editing. Jeanne Duus Johansen: Supervision; methodology; writing – review and editing. Jakob Ferløv Schwensen: Supervision; investigation; methodology; writing – review and editing. We would like to thank the patient for letting us share his story, patch test results, and clinical pictures. The authors declare no conflict of interest.