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

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.

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.

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.