Systemic Nickel Allergy Syndrome

Nickel is the metal that most frequently causes allergic reactions since it is a ubiquitous metal that can be found in many objects and foods. Due to its ubiquity Nickel allergy is one of the most frequent occupational disease. The major manifestations of nickel allergy is the Allergic Contact Dermatitis (ACD), but a number of Ni-DAC patients shows the appearance of symptoms (eczema, urticaria, flare up of previous positive patch tests and other skin manifestations, abdominal pain, diarrhoea or constipation, sometime headache and other minor symptoms) also after ingestion of Ni-containing foods. This condition is called Systemic Nickel Allergy Syndrome (SNAS) (or Systemic Contact Dermatitis-SCD). The syndrome can be observed in vivo after oral provocation test. Many authors administer for this purpose 0.3 to 10 mg Ni and the subsequent syndrome seems correlated to the amount of nickel administered. There are no specific laboratory data so the oral challenge is the gold standard in the diagnosis. The patho-physiology of SNAS is quite different from the Ni-allergic contact dermatitis, in fact, SNAS is characterized by a significant increase of IL-5 and other Th2 cytokines in serum after challenges. It has been observed also modification in the CD expression in lymphocytes of SNAS patients respect to the ACD patients and healthy controls both in the blood and in the gastrointestinal mucosa.  The possibility for sensitized workers to develop SNAS has to be taken into account for secondary prevention and for legal purposes.