Oral allergy syndrome and pollen-food syndrome — formative SAQs

SAQ 1 — Recognise and risk-stratify (10 marks)

A ten-year-old with spring birch-pollen rhinitis gets lip tingling, palate itch and throat tightness within a minute of eating a raw apple at school. She eats baked apple every week with no symptoms. Her mother asks whether this is dangerous and what she should do. ^{[1] [2]}

Questions

1. What is the most likely diagnosis, and which mechanism explains why the cooked apple is tolerated? (3 marks) ^{[1] [2]}

2. Outline the immediate advice and the definitive management plan for this low-risk phenotype. (4 marks) ^[12]

3. State three features in the history that would escalate this child out of the low-risk pathway, and what each implies. (3 marks) ^{[10] [13]}

Model answer

Diagnosis and mechanism (3). This is pollen-food allergy syndrome (oral allergy syndrome), driven by cross-reactivity between the major birch allergen Bet v 1 and the apple PR-10 protein Mal d 1. The protein is heat-labile and digestion-labile, so cooking denatures it and the cooked apple is tolerated — the defining 'raw but not cooked' history. ^{[1] [2]}

Immediate and definitive plan (4). Stop the raw apple, rinse the mouth, and give a non-sedating oral antihistamine for breakthrough oral symptoms. Confirm pollen sensitisation and the phenotype with a fresh-food prick-prick test (more sensitive than commercial extracts for labile proteins) and component-resolved diagnostics (rBet v 1, rMal d 1). Dietary advice: avoid the raw apple, keep cooked and peeled forms, and do not over-restrict tolerated foods. Provide a safety-net plan to return if any systemic symptom appears. ^[12]

Escalating features (3). Urticaria beyond the mouth, wheeze or collapse — these are systemic, so treat as anaphylaxis with IM adrenaline. Reaction to the cooked apple or to small amounts — suggests a primary food allergy or a heat-stable lipid transfer protein phenotype rather than classic PFAS. Cofactors such as exercise or NSAIDs preceding a systemic reaction — flag a cofactor-dependent or LTP phenotype and lower the threshold for adrenaline. ^{[10] [13]}