Mechanism and diagnosis of protein contact dermatitis

Protein contact dermatitis (PCD) is a chronic eczema because of immediate hypersensitivity to protein and not related to haptens. As it has to be diagnosed by prick tests, it is probably under-recorded and under-estimated that is why it is important for dermatologists, allergists and occupational physicians to better know this peculiar contact dermatitis.

Some recent series have emphasized that PCD is mainly an occupational dermatosis, mainly observed in food handlers.

PCD is a chronic eczematous dermatitis, possibly exacerbated by work, suggested if associated with inflammatory perionyxis (paronychial inflammation) and immediate erythema with pruritis, to be investigated when the patient resumes work after a period of interruption. Prick tests with the suspected protein-containing material are essential, as patch tests have in most of the cases negative results. Prick-by-prick tests with fresh material are recommended. The product has to be 'pricked', for instance the food, and immediately after the forearm is pricked. In case of multisensitization revealed by prick tests, it is advisable to analyse IgE against recombinant allergens. History of atopy found in 56--68% of the patients has to be checked for. Most of the cases are observed among food-handlers but PCD can also be because of nonedible plants, latex, hydrolyzed proteins or animal proteins.