The cow's milk allergy that wasn't: allergy to supplemental oral lactase enzyme.

Background: Allergy to supplemental lactase is sparsely reported in the literature with only one prior case of anaphylaxis documented [2]. Reactions to this agent can occur following cow's milk ingestion which could lead to an erroneous diagnosis of cow's milk allergy in the absence of another explanation.

Case presentation: Our patient, a 48-year-old male with eczema, exercise-induced asthma and rhinoconjunctivitis, presented with four episodes of systemic reactions characterized by mucosal swelling and asthma symptoms following ice-cream exposure. It was later recognized that he had been taking a lactase enzyme supplement just prior to all of his reactions. Epicutaneous testing was strongly positive to a saline slurry of the lactase supplement he had been using. The patient has been avoiding supplemental lactase since with no subsequent reactions.

Discussion: Our patient was diagnosed with an allergy to supplemental lactase enzyme on the basis of convincing Immunoglobulin E (IgE) mediated symptoms and positive skin testing. He continued to eat cow's milk products, ruling out an IgE-mediated allergy to cow's milk. In the literature, there is one prior case of anaphylaxis documented. Another case of localized oropharyngeal symptoms described in the literature was thought to be a form of oral allergy syndrome as the patient had positive epicutaneous testing to Aspergillus oryzae-derived lactase as well as Aspergillus species. Occupational sensitization, rhinitis/asthma, and protein contact dermatitis have also been detailed in the literature. Although rare, this case highlights the importance of a thorough history of over-the-counter supplements when assessing a patient with features of anaphylaxis.