If the clinical appearance is consistent with contact eczema, the next step is to decide if the eczema is of occupational origin.
It is essential to take an occupational history of the patient involving questions about workplace exposures to potential cutaneous irritants or allergens. In this process, safety data sheets (SDSs) are very useful. A history of non-occupational or recreational exposures and even the use of personal care products and topical medications should be included to exclude them as probable causes. A work-related contact eczema can be indicated by a history where the eczema worsens when at work and exposed to the suspected irritant or allergen, and improves when the patient is away from work. The anatomical localization and distribution of the eczema may also provide information about a possible work relation, since skin covered by clothing is seldom a primary sites for occupational eczema. In addition, eczema consistent with cutaneous exposure in relation to particular job tasks is suggestive of a work relation for the condition. The timing of the first appearance of the eczema is also important because, while the disease can arise at any time during employment, a worker seems to be at greater risk for developing contact eczema during the first 3-12 months in a new job.
As we have mentioned before, irritant and allergic contact eczemas are morphologically indistinguishable. The distinction between the two is important, however, when it comes to how to advise a worker who has a work-related eczema.
No diagnostic test can confirm irritant contact eczema. Allergic contact eczema, however, can be confirmed by a patch test. Patch tests are not the same as skin prick tests, which are used to diagnose type I allergy. Allergic contact eczema is caused by a type IV allergy, and dependent upon a previous sensitization to a contact allergen. The principle for the patch test is to expose the patient to low levels of potential allergens. During the test, the test exposure levels have to be below the threshold for both contact sensitivity and contact irritation, but still capable of eliciting a reaction in an already sensitized patient.
More than 4300 chemicals have been identified as contact allergens. Standard series of the most common sensitizers in the environment are used as an initial patch test screening for possible allergic contact eczema. In the occupational setting additional series cover the most prevalent contact allergens found in different occupations. Examples of additional series are Oil & Cooling Fluid, Plastic & Glues, Rubber Additives, Isocyanate, Epoxy, Plant, Metal, Bakery and Hairdressing series.
Patch testing is a specialized test performed by dermatologists. The most commonly accepted technique involves the application of test allergens under occlusion onto the skin of the upper back for two days.
© G. Tjalvin
The relevance of a positive patch test has to be established for suspected occupational allergens, preferably given by safety data sheets (SDSs). It is important to keep in mind that a positive patch test only tells us that the patient has, at some point, been sensitized to a specific chemical. A diagnosis of allergic contact eczema has to be confirmed by clinical manifestations and relevant work exposure.
© University of Bergen/Author: G. Tjalvin.