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]

SAQ 2 — The lipid-transfer-protein phenotype (10 marks)

A fourteen-year-old presents with generalised urticaria, wheeze and dizziness minutes after eating a peach (with the skin on) at a picnic, having earlier taken ibuprofen and gone for a run. She has previously reacted to raw peach but tolerates most birch-related fruits cooked. [10]

Questions

1. How does this presentation differ from classic oral allergy syndrome, and which protein is most likely responsible? (3 marks) [10]

2. Outline the acute management and disposition. (4 marks) [13]

3. Describe the long-term plan, including the role of component-resolved diagnostics and adrenaline. (3 marks) [4] [10]

Model answer

Difference and protein (3). This is a systemic reaction, not classic local OAS. The trigger (peach with skin), the cofactors (ibuprofen, exercise), and the systemic features point to lipid transfer protein allergy (Pru p 3). LTP is heat-stable and digestion-stable, survives to be absorbed intact, and can cause anaphylaxis — which is why it is classified apart from classic pollen-food syndrome. [10]

Acute management and disposition (4). This is anaphylaxis — a clinical diagnosis. Give IM adrenaline into the anterolateral thigh first (roughly 0.01 mg/kg of 1:1000, or a weight-banded autoinjector: 0.30 mg at her weight); call for help; lie flat with legs elevated if shocked; high-flow oxygen and IV fluids for shock; bronchodilator adjunctive for wheeze. Repeat adrenaline at five minutes if no response. Observe for at least six hours and admit, because this is a severe systemic reaction with cofactors and possible recurrence. [13]

Long-term plan (3). Avoid peach in all forms (raw and cooked), since LTP is heat-stable. Use component-resolved diagnostics (rPru p 3) to confirm the phenotype and screen for cross-reactive LTP foods. Provide a written anaphylaxis action plan (ASCIA/BSACI/FARE) with her photo and allergen, prescribe two weight-banded adrenaline autoinjectors, train her and her family, and educate the school. Review periodically, especially around cofactor exposure, and consider specialist pollen immunotherapy referral. [4] [10]