For this child, the initial presentation and evidence for sensitization against lysozyme, in the context of an egg allergy, are compatible with the diagnosis of anaphylaxis to lysozyme. Within the hours before the reaction, he did not ingest any food containing eggs, wheat, fish, or milk and had a usual meal for dinner two hours before intake of the drug. When giving this treatment to her son, his mother had no idea that it could contain egg protein and she did not perceive lysozyme as an allergenic protein. However, the box mentioned the presence of lysozyme and also specified ”contains lysozyme extracted from egg”. Previous reports have described anaphylaxis attributable to lysozyme. One case of anaphylaxis following the ingestion of Lizipaina® for a mild respiratory infection was reported for a 15-year-old egg-allergic patient sensitized to lysozyme⁴. The SPT was positive for Lizipaina® and sIgE against lysozyme was detected. Another case of anaphylaxis to Lizipaina® was described in a 54-year-old patient sensitized to lysozyme. The SPT was positive for lysozyme (commercial extract) and sIgE against lysozyme was detected. This patient experienced similar symptoms 3 to 4 times after the ingestion of cured cheese or raw egg⁵. A six-year-old egg-allergic child presented with anaphylaxis 5 mins after the first use of a deodorant containing lysozyme hydrochloride, but no lysozyme sensitization was demonstrated, either by SPT or sIgE measurement⁶. Other cases of allergic reactions potentially related to lysozyme were described for women using vaginal suppositories containing lysozyme, among whom three were known to be allergic to egg. However, these suppositories contained other egg proteins, which may have been involved in the occurrence of the allergic reactions, and none of these patients was sensitized to lysozyme⁷. In the child of the case presented here, symptoms may have been worsened by the presence of a concomitant infection. Despite the presence of lysozyme in various industrial food products, our patient may have not been previously exposed because of his large food restrictions and his aversion to dairy products. It is also possible that he may simply not have reacted to previous exposure because the amount of lysozyme contained in food products is too low to induce an allergic reaction compared to the 20 mg contained in Lysopaine®.

In summary, lysozyme may induce anaphylaxis in egg-allergic patients, especially when aggravating factors, such as infection, are present. Lysozyme can be found in many commonly consumed industrial food and drug products and its labelling may be misleading, exposing patients to potentially severe reactions. Indeed, lysozyme is not necessarily perceived by egg-allergic patients as an allergenic protein. Our observation highlights the importance of properly educating allergic patients to recognize allergens, even minor ones.