Numerous epidemiologic studies on contact dermatitis show that sensitization to nickel is highly prevalent in Europe.1–3 Since this information is usually retrieved from data on patients with skin complaints who have been referred for patch testing, it does not generally apply to patients who consult directly for nickel-induced contact dermatitis, even if they are sensitized to nickel.

It is important to differentiate between prevalence of sensitization and prevalence of allergic contact dermatitis; hence the key role of relevance in positive patch test results.

In the case of nickel-induced allergic contact dermatitis, a colorimetric approach—the dimethylglyoxime spot test—can be used to determine the involvement of various metal objects in a skin disease. Not all objects that contain nickel necessarily release nickel. Those that do can be rapidly indentified using this simple test, which demonstrates the reaction between nickel and dimethylglyoxime by the formation of a reddish-brown precipitate.

Systematic implementation of this test would prove extremely useful when attempting to determine the cause of a skin disease and even for ascertaining which objects are causing contact dermatitis.

We performed a descriptive, observational, and retrospective study to evaluate nickel-induced contact dermatitis as the main presenting complaint in the skin allergy section of the dermatology department.

We collected data from the patients examined using the GEIDAC standard series between 2000 and 2010 (1283 men [37.7%] and 2121 women [62.3%]). The mean age of the population was 48.3 years.

Of the 3404 patients, 2092 (61%) had at least 1 positive patch test result for an allergen included in the standard series; in 824 patients (24.2%), the positive result was with 5% nickel sulfate in petroleum jelly.

However, it is noteworthy that an association between sensitization and the presenting skin complaint was demonstrated in only 57 of the 824 nickel-sensitized patients (6.9%). The nickel allergy was considered occupational in 9 of the 57 patients (15.8%) (Table 1) and nonoccupational in 48 patients (84.2%) (Table 2).

Both tables show clinical data from patients with positive patch test results with present and definite relevance (positive dimethylglyoxime test result) and probable relevance (negative dimethylglyoxime test result). The dimethylglyoxime test made it possible to investigate the release of nickel from the metal objects brought by the patients in 65 of 68 cases. The test result was positive in 57 cases and negative in 8 cases.

In other words, of the 824 patients who were sensitized to nickel, the presenting skin complaint was shown to be induced by nickel in the objects handled in 57 cases; in the remaining 8 cases, sensitization to nickel was probably associated with the presenting skin complaint, that is, the dimethylglyoxime test result was negative, but the skin complaint resolved when the patient stopped using the causative object.

In the 57 cases of nonoccupational allergic contact dermatitis of present relevance, the association between dermatitis and the use of various objects and garments was demonstrated, and the site of the dermatitis coincided with the area of contact with the metal objects (eg, buckle with abdomen and key ring with thigh).

Many of the patients with nickel-induced allergic contact dermatitis simultaneously presented other skin complaints, and even systemic manifestations not associated with allergy to metal (dyshidrotic eczema [8 cases], constitutional eczema [8 cases], contact eczema caused by other allergens [7 cases], atopic dermatitis [4 cases], polymorphic light eruption [1 case], occupational asthma [1 case], and pressure urticaria [1 case]).

Evaluation of the relevance of a positive result is the most difficult part of the patch test procedure. It depends on the skill, experience, and curiosity of the researcher, and, particularly in a case of past relevance, on the patient's memory.

The first data on sensitization to nickel in Spain were reported in 19764; however, the clinical relevance of this sensitization was not included in the epidemiologic studies of the GEIDAC until 1996,5 when, of the 3386 patients examined, 993 (29.3%) were sensitized to nickel; of these, 37% had present and positive relevance, ie, they consulted for allergic dermatitis caused by contact with nickel.

A subsequent study by GEIDAC in the year 20016 showed similar percentages of sensitization (26.64%) and of present positive relevance (36.38%).

In the year 2008, the Spanish Surveillance System on Contact Allergies (REVAC)7 reported that the frequency of sensitization to nickel was 25.4%. Relevance was present in 32% of the 295 patients sensitized to nickel.

Over a period of 10 years (2000-2010), we found a very similar percentage (24.2%) in 3404 patients. However, we only found present relevance in 6.9% of the 824 positive cases. We believe that this difference is due to the subjectivity involved in determination of present relevance, which may be definite (dimethylglyoxime test), probable (clearly observable clinical course), or only possible (eg, frequent contact with coins in hand eczema).8 We only included patients with definite present relevance. In other studies, it is possible that relevance was considered present when it was only probable or possible. This observation could explain the disparate percentages for positive and present relevance (7.89% vs 36.38% and 32%). It is also noteworthy that, for patients whose sensitization was of present relevance, none of the previous studies6,7,9 established the site, specific origin, or cause of the eczema, as we did.

Similarly, Spanish epidemiologic studies do not state that authors use the dimethylglyoxime test routinely in their clinical practice. In our opinion, the fact that a patient has come into contact with a metal object (eg, stainless steel, which is a nickel-containing alloy) does not mean that this object caused his/her dermatitis. Alloys with high nickel content do not always release nickel, or if they do, they do so in amounts of less than 5mg/cm2/wk, which is the minimum quantity for triggering dermatitis in a patient who was previously sensitized to this metal.10

The dimethylglyoxime test has a specificity of 97.5%, although its sensitivity is only 59.3%.11

In summary, we performed an observational and retrospective study by collecting data on patients sensitized to nickel in our hospital from January 2000 to December 2010 in order to ascertain which of these patients genuinely had allergic contact dermatitis due to this metal and how many consulted for this reason. We emphasize the usefulness of the dimethylglyoxime test when attempting to establish the relevance of a positive nickel patch test result. The test could even prove useful to identify the object responsible for the patient's dermatitis.

The authors declare that they have no conflicts of interest.