Allergic contact dermatitis to zinc caused by silver ring splint: Exposure assessment with scanning electron microscope

The patient, a 46-year-old woman with Ehlers–Danlos syndrome with a previous history of scalp psoriasis in her younger years and without any personal or family history of atopic disease, was referred to the Department of Dermatology with complaints of swelling and erythema on both hands. She receives disability benefits and has no occupational history of relevance. Medical history revealed that due to Ehlers–Danlos syndrome, she used a hand orthosis, 'Silversplint' (Figure 1). The patient reported that soon after starting using the orthosis, she experienced itching, swelling and erythema in the same areas where the skin was in direct contact with the orthosis. Moreover, she experienced worsening of symptoms after contact with water, during cooking and housework. She also reported of itching and swelling when using earrings and necklaces made of silver. Apart from cooking, she has no leisure activities where she comes in contact with metallic objects. Her symptoms were localised to the areas in close contact to the orthosis, and started after approximately 1 h of usage and persisted for 2–3 days. Clinical examination showed eczema of the dorsal aspect of distal interphalangeal phalanges joints 1–4 fingers, on both hands. Vaseline was tried as a barrier cream without effect. Topical corticosteroids were recommended, but not used by the patient. Suspicion of irritative contact dermatitis due to occlusion was raised. To confirm the diagnosis and rule out allergic contact dermatitis, the orthosis manufacturer was contacted. It revealed that the sliversplint was composed of only silver, and a piece of silver from the ring splint was kindly provided. Scanning electron microscope (SEM) using a Hitachi SU6600 field emission SEM (Hitachi, Tokyo, Japan) equipped with an energy-dispersive x-ray (EDX) detector (Bruker Nano GmbH, Berlin, Germany) was used for further composition assessment. The silver piece was fixed on a 10 mm Al stub covered with double-sided carbon adhesive discs (Agar Scientific, Ltd.). To ensure good conductivity between the silver piece and the Al stub, spots of carbon cement were added. Analysis of two of three different areas from the silver piece revealed the presence of zinc, copper and silver (Figure 2, right). Epicutaneous testing was accordingly performed following ESCD guidelines1 with the European baseline series (S-1000), silver nitrate, copper(II) sulphate pentahydrate, zinc chloride 1.0% and zinc 2.5% from the metal series (MET-1000) (Chemotechnique Diagnostics, Vellinge, Sweden), test substances were applied to the upper back for 48 h in Finn Chambers (SmartPractice, Phoenix, AZ) on Scanpor tape (Norgesplaster, Vennesla, Norway). A piece of silver from the patient ring splint was applied on the volar side of the right forearm. Positive reaction (+) to zinc chloride 1.0%, zinc 2.5% and to the silver piece, observed on Day 3 and Day 7, were considered relevant. All other tests were negative. The silversplint was fully replaced by a yellow gold splint and the eczema resolved. The most common metals for causing allergic contact dermatitis are nickel, cobalt and chromium.2 Allergic contact dermatitis to zinc is rare.3 To our knowledge, this is the first report of allergic contact dermatitis to zinc due to the use of sliversplints. Allergic contact dermatitis (ACD) due to zinc from dental fillings has been reported to induce oral lichen planus, palmoplantar pustulosis and maculopapular rash.4 Systemic allergic dermatitis due to zinc ingestion has also been reported.5, 6 Contact allergy to nickel and/or to the most common metals causing contact allergy1 is an important differential diagnosis in this case, as nickel is often part of the zinc sealing when a darker appearance is required (Figure 1). Moreover, the scratches in the silver surface (Figure 2) could facilitate the release of several metal ions, especially in this case where the eczema worsened after contact with water. However, in our patient, epicutaneous testing with the European baseline series did not reveal a contact allergy to nickel. In a hypothetical case of positive contact allergy to nickel, the dimethylglyoxime (DMG) nickel spot test would have been useful to determine the potential release of nickel, bearing in mind that the DMG test has a high specificity, but modest specificity.7 This case illustrates the importance of systematic stepwise exposure assessment8 and performing exposure analysis in the diagnosis of allergic contact dermatitis. In this case, point analysis of metal material with SEM–EDX was useful to find the presence of zinc and subsequent epicutaneous testing. The peak of Cu is quite broad in the EDX chromatogram (Figure 2, right). Since copper has a Kα peak at 8.040 and nickel has its Kα peak at 7.471, the two peaks could be separated from one another in our spectra. In the lower range of the spectra, the Lα lines may be more difficult to separate (0.851 and 0.930 for copper and nickel, respectively). We did look at this closer to see whether the nickel peak could be hidden inside of the copper peak, but this seems not to be the case for the spectra that were collected. The spectra were further deconvoluted, which may help to recognise whether elements have been overlooked or if any elements are identified wrongly. In any case, SEM–EDX is a point analysis, and we cannot rule out the possibility that there may be traces of nickel also present. However, our EDX spectra and the deconvolution method showed no sign of nickel. SEM material analysis has been previously used to assess the morphology of glass fibres in glass fibre dermatitis,9 allergic contact dermatitis to nickel, chromium and gold10 and lymphocytoma cutis induced by allergic contact dermatitis to zinc and gold.11 Clinical suspicion of metal allergy should include stepwise exposure assessment,8 spot tests7 special tests when available, targeted epicutaneous testing1 and counselling for the purposes of secondary and tertiary prevention. Nerea M. A. Bratteland: Writing – original draft; writing – review and editing; resources. Torun K. Ervik: Investigation; writing – review and editing; supervision; data curation. Jose H. Alfonso: Writing – review and editing; investigation; supervision; resources; project administration; methodology; data curation; conceptualization; funding acquisition. Jose H. Alfonso has received an unrestricted research grant from Sanofi. Other authors declare no conflicts of interest.