Detection of culpable food(s) in patients with suspected food anaphylaxis can be difficult since both open and blind challenges might be impossible or unethical. This is a topical issue, considering allergen cross-reactivity between foods and inhalant allergens, the knowledge of which is of paramount importance in avoidance of dangerous foods. Allergy to the cashew nut and other plants belonging to the Anacardiaceae family (1) is well known.
Belonging to the Terebinthales order, the Anacardiaceae family includes edible species from the genera Pistacia, Mangifera, and Anacardium (Table 1).
|Pistacia**||P. lentiscus||Lentiscus||Resin with expectorant properties can be obtained from bark|
|P. terebinthus||Terebinthus||Resin with balsamic and expectorant properties can be obtained from (Chios or Cyprus Trementin)|
|P. vera||Pistachio*||Seed can be eaten as it is or used for preparing pastry, ice cream, and sauces|
|P. chinensis||Grown in Italy as ornamental plant|
|Rhus||R. coriaria||Sommacchus||Important source of tannin|
|Toxicodendron||T. verniciflua||Chinese lacquer can be obtained from tree; it contains volatile compound |
toxicondendrol, which can cause contact dermatitis
|Schinus**||S. molle||False pepper||Grown as ornamental plant|
|Anacardium||A. occidentale||Acajou*||Seeds usually eaten as snack with drinks|
|Cashew nut or apple|
|Schinopsis||S. balansae||Quebracho||Hard, heavy wood|
Pistacia vera, i.e., the pistachio nut, is a tree native to the Middle East, but it is cultivated also in Italy, mainly in Sicily. The pistachio is a green, elongated nut, used in pastry, ice cream, and sauces, or as an appetizer.
The Mangifera genus includes the mango (Mangifera indica or M. laurina), a tropical fruit with an orange core and a sour taste.
Anacardium occidentale, commonly known as the cashew nut, is eaten as a snack with drinks.
Other, nonedible Anacardiaceae species products (such as balsamic resins from Terebinthus plants and Chios turpentine) are used in natural medicine for their expectorant properties; other plants of this family are cultivated for ornamental (lentiscus, Pistachio chinensis, scotanus, false pepper) and industrial (tannin from Sommacchus; glossy black varnish from Toxicodendron; a very strong wood called quebracho from Schinopsis) purposes.
We describe the case of a patient allergic to pistachio who had anaphylaxis due to cashew nuts. A 42-year-old white man was admitted to our emergency room complaining of mouth and lip itching, slurred voice, dyspnea, and vomiting a few minutes after eating some cashew nuts. Prompt treatment with steroids, antihistamines, and epinephrine relieved the patient's symptoms, leading to a complete recovery in about 24 h.
After some weeks, the patient underwent a careful allergy examination at our allergy clinic. History disclosed three previous episodes of adverse reactions to pistachio. At the age of 30 years, when eating chocolate and hazelnut candy, the patient reported suffering strong mouth itching followed by vomiting.
Three years later, the patient complained of the same symptoms while eating pasta with a sauce based on garlic, basil, and pine nuts and attributed the symptoms to pine nuts and basil. After a few months, mouth itching and vomiting occurred again when the patient ate pistachio nuts.
The patient inquired into the ingredients of the provoking foodstuffs and found that the candy contained pistachio extract and that pistachio nuts had been used for the pasta sauce. The patient then held pistachios responsible for his previous adverse reactions and carefully avoided them without undergoing any allergy evaluation.
No other diseases were reported by the patient. In particular, he had never complained of allergy symptoms or skin diseases such as contact dermatitis or urticaria in the past.
In consideration of reported cross-reactions between pistachio nuts and Artemisia (2) and Parietaria (3) pollens, a skin prick test with commercial extracts for a panel of inhalant allergens (including pollens, dust mites, and mycophytes) was performed. Only a weak positivity for dust mites was found; pollens and mycophytes were negative, thus excluding pollinosis.
To diagnose an adverse reaction to Anacardiaceae, a skin prick by prick test (according to Dreborg & Foucard  was performed with a positive result for pistachio and cashew nut and a negative result for mango pulp and peel; prick by prick testing for mango seed, performed in a second session (as reported in ref. 5) was positive. Specific serum IgE levels to pistachio and cashew nut, evaluated by CAP-RAST (Pharmacia Diagnostics AB, Uppsala, Sweden), were normal, as they were for pollens, mycophytes, and mites.
The following conclusions can be drawn:
In a patient with severe allergic reactions to a food derived from the Anacardiaceae family, the safest diagnostic test appears to be the fresh food skin test.
All food derived from the same botanic family should be tested even if the reaction occurred to only one of them; moreover, all parts of the vegetable (skin, pulp, and seed) should be tested.
The patient must be carefully informed about diet restrictions and modifications: on the one hand, all cross-reacting foods derived from the same botanic family must be eliminated; on the other hand, the patient must be aware of hidden allergens contained in industrially prepared foods (such as snacks, sauces, pastry, and candies), since all the ingredients are not always reported on food labels (6).