D3.278 - Tropomyosin-Driven Cross-Reactivity Between Shellfish and House Dust Mites: A Case Report

Background:Shellfish such as shrimp, crab, and lobster are common triggers of food-induced allergic reactions. Tropomyosin is the major allergen responsible for shellfish allergy and represents a pan-allergen widely distributed among invertebrates, including crustaceans, house dust mites, insects, and mollusks, leading to IgE-mediated cross-reactivity.

Case Presentation:A 40-year-old male presented with recurrent episodes of oral and labial pruritus, perioral erythema, and swelling after consuming various seafood products. Two weeks prior, ingestion of shrimp and squid caused oral itching, perioral edema, wheezing, throat swelling, and dyspnea, requiring emergency department treatment with intravenous fluids, pheniramine, and dexamethasone, resulting in symptom resolution.

The patient had no history of asthma, drug allergy, or allergic rhinitis. Spirometry was normal. Laboratory findings showed total IgE 37.5 IU/mL (0–160), eosinophils 0.52 ×10⁹/L (0–0.7), and serum tryptase 4.23 µg/L (<11.4). Skin prick testing was positive for Dermatophagoides pteronyssinus. Component-resolved diagnostics (ALEX) demonstrated specific IgE positivity to Der p 10 (2.85 kUA/L), Blo t 10 (4.51 kUA/L), Ani s 3 (3.23 kUA/L), Pen m 1 (1.29 kUA/L), and Per a 7 (2.46 kUA/L). Additional sensitization was detected to crab (Chi spp.) 1.33, shrimp (Lit s) 2.09, lobster (Hom g) 0.56, squid (Lol spp.) 0.43, mussel (Myt e) 0.53, scallop (Pec spp.) 0.67, and oyster (Rud spp.) 0.36 kUA/L.

Based on clinical history and test results, strict avoidance of shellfish and mollusks was advised. The patient was educated regarding allergen disclosure in restaurants, prevention of cross-contamination, and emergency management. Due to a history of severe allergic reactions involving respiratory symptoms, intramuscular adrenaline was emphasized as first-line treatment for anaphylaxis, and an adrenaline auto-injector was prescribed.

Conclusion:

Tropomyosin-specific IgE positivity in individuals sensitized to shellfish may be associated with relatively elevated mite-specific IgE levels; however, this finding may lack clinical correlation. In such cases, tropomyosin positivity represents laboratory cross-reactivity rather than clinically relevant allergy, highlighting the pivotal role of clinical history in accurate diagnosis.