ABSTRACT
A 46-year-old man with no known allergies or history of atopy was referred for the investigation of a severe anaphylactic reaction following root canal dental treatment. The procedure had been done under local anaesthetic and involved drilling the tooth, removal of dental pulp, cleaning and insertion of a temporary filling. Preliminary skin prick tests (SPTs) and intradermal tests were negative to natural rubber latex, articaine (the local anaesthetic used for his procedure), lidocaine and chlorhexidine. He had negative specific IgE to chlorhexidine and latex, and a negative lidocaine challenge, confirming that he was not allergic to lidocaine. He returned for further dental treatment, which was done without local anaesthetic. As the procedure was completed, he developed severe anaphylaxis again. He made a full recovery and his dentist was asked for detailed information and samples of all the materials used during the procedure. Subsequent SPT showed a positive weal of 12 x 6 mm to the dental lubricant, Glyde, which was used on both occasions. Its ingredients included polyethylene glycol (PEG) 4253. SPT to other high-weight macrogol-containing products showed positive reactions to a 5% lidocaine ointment, Movicol, EMLA cream and Depomedrone. On further questioning he recalled minor immediate irritation after using a brand of children's shampoo, but a SPT to the shampoo was negative. An open test, closed test and SPT to a lower-molecular-weight patch-test allergen (PEG400 in petrolatum) were negative. PEGs or 'Macrogols' are hydrophilic polymers used in food, cosmetics and pharmaceutical reagents. They have recently attracted attention as they are excipients in several COVID-19 vaccines and have been suggested as a possible cause of anaphylaxis. Anaphylaxis to higher-molecular-weight PEGs has been reported from the use of bowel preparations and parenteral steroids. There are a handful of reports of contact urticaria to PEG-containing medicaments. We report this case to raise awareness of severe immediate hypersensitivity to these apparently innocuous ingredients and a novel source of exposure. A low index of suspicion, lack of standardized nomenclature and commercial reagents for testing are current barriers to diagnosis.