What is the treatment for a groin reaction to shellfish?

Treatment of Groin Reaction to Shellfish

Administer intramuscular epinephrine 0.3-0.5 mg immediately into the anterolateral thigh if any signs of systemic involvement are present, as this is a life-threatening emergency requiring prompt recognition and treatment. 1, 2

Immediate Assessment and Classification

The first critical step is determining whether this represents localized urticaria/angioedema versus anaphylaxis:

• Anaphylaxis is likely if the groin reaction (skin/mucosal involvement) occurs with rapid onset after shellfish ingestion AND is accompanied by any of the following: 1

  • Respiratory compromise (dyspnea, wheezing, stridor, throat tightness)
  • Cardiovascular symptoms (hypotension, syncope, dizziness)
  • Persistent gastrointestinal symptoms (severe cramping, vomiting, diarrhea)

• Shellfish is the most common cause of anaphylactic episodes in adults, making systemic involvement highly concerning in this context 1, 2

Treatment Algorithm Based on Severity

For Anaphylaxis (Multi-System Involvement)

Epinephrine is the only first-line treatment and must be administered immediately—antihistamines alone are insufficient and potentially dangerous. 2, 3

• Dose: 0.3-0.5 mg (0.3-0.5 mL) of undiluted epinephrine intramuscularly into the anterolateral thigh 4
• Repeat every 5-10 minutes as necessary based on clinical response 1, 4
• Call 911 immediately and transport to emergency department even if symptoms improve, as biphasic reactions occur in up to 20% of cases 3
• Administer supplemental oxygen and place patient supine with legs elevated 1
• Antihistamines (diphenhydramine 25-50 mg) and H2-blockers are adjunctive only, never primary treatment 2, 3

For Isolated Localized Reaction (Groin Area Only)

If there is no respiratory, cardiovascular, or gastrointestinal involvement:

• Oral diphenhydramine 25-50 mg as first-line treatment 3
• Consider adding ranitidine 50 mg (H2-antihistamine) for enhanced histamine receptor blockade 3
• Oral prednisone 0.5 mg/kg may be added for extensive swelling or persistent symptoms 3
• Observe for minimum 4-6 hours to monitor for progression to anaphylaxis or biphasic reaction 3

Critical pitfall: Do not mistake early anaphylaxis for a simple allergic reaction. Even if symptoms initially appear localized, progression can be rapid and life-threatening. 1, 3

Post-Acute Management (All Patients)

Regardless of initial severity, all patients with shellfish reactions require:

• Prescription for two epinephrine autoinjectors (0.3 mg for adults) to carry at all times, as future exposures carry risk of life-threatening anaphylaxis 2, 3
• Mandatory referral to allergist-immunologist for comprehensive evaluation including skin prick testing and development of emergency action plan 2, 3
• Education on strict shellfish avoidance, including cross-contamination risks and reading food labels 1
• Medic Alert identification jewelry documenting shellfish allergy 1

Important Clinical Considerations

• Reactions typically occur within minutes to 1 hour after ingestion, though can be delayed up to several hours 1
• Cross-reactivity is unpredictable among different shellfish species (shrimp, crab, lobster, clams, oysters) and requires individual testing 1
• Patients with asthma are at higher risk for severe reactions and fatal outcomes 1
• Serum tryptase levels (if obtained 1-2 hours after symptom onset) can help confirm anaphylaxis diagnosis retrospectively, but should never delay treatment 1

Common error to avoid: Shellfish allergy does NOT indicate iodine allergy or increased risk of radiocontrast reactions—these are unrelated conditions that should not be conflated in medical documentation. 1, 5