What is the emergency department management for a patient with angioedema caused by caterpillar (setae) exposure?

Emergency Department Management of Caterpillar-Induced Angioedema

Caterpillar-induced angioedema should be managed as histamine-mediated allergic angioedema with immediate airway assessment, epinephrine administration for significant symptoms, and standard allergy treatments including antihistamines and corticosteroids. 1, 2

Immediate Airway Assessment

• Assess airway patency immediately upon presentation, as this is the most critical first step for any angioedema patient 3
• Monitor closely for signs of impending airway closure: voice change, inability to swallow, dyspnea, stridor, or drooling 3, 4
• Consider elective intubation before complete obstruction occurs if any warning signs are present 3, 4
• Awake fiberoptic intubation is optimal to reduce risk of worsening edema 4
• Avoid direct laryngoscopy unless absolutely necessary, as instrumentation can exacerbate angioedema 3, 4
• Ensure backup tracheostomy equipment is immediately available 3, 4

Classification: Histamine-Mediated Angioedema

Caterpillar setae (hair/spine) exposure causes type I allergic reactions, making this histamine-mediated angioedema. 1 Key distinguishing features include:

• Rapid onset within minutes of exposure 2
• Concomitant urticaria and pruritus are common (present in ~50% of allergic angioedema cases) 1, 2
• Clear exposure history to caterpillar contact 1
• Responds to standard allergy treatments 2

First-Line Pharmacological Treatment

For Significant Symptoms or Any Airway Involvement:

• Administer epinephrine (0.1%) 0.3 mL intramuscularly immediately 3, 4, 5
• Epinephrine is FDA-approved for emergency treatment of allergic reactions including angioedema from insect/arthropod exposure 5
• Do not delay epinephrine administration if airway compromise is suspected 3

Standard Adjunctive Therapy:

• IV diphenhydramine 50 mg (H1 antihistamine) 3, 6
• IV methylprednisolone 125 mg (corticosteroid) 3, 6
• Ranitidine 50 mg IV or famotidine 20 mg IV (H2 blocker) 3, 6
• High-humidity face tent for symptomatic relief 7

Observation and Monitoring

• Observe for minimum 4 hours after treatment initiation, as most histamine-mediated angioedema resolves within 24-48 hours 7
• Extended observation (several hours minimum) is required for oropharyngeal or laryngeal involvement 3, 4
• Monitor vital signs continuously during acute phase 3
• Patients with minimal residual symptoms after 4 hours may be discharged with caution about low risk of delayed reaction 4

Critical Pitfall to Avoid

Do not confuse caterpillar-induced angioedema with bradykinin-mediated angioedema. Unlike hereditary angioedema or ACE-inhibitor angioedema, caterpillar exposure causes histamine-mediated reactions that respond well to epinephrine, antihistamines, and corticosteroids. 1, 2 The presence of urticaria, pruritus, rapid onset, and clear allergen exposure (caterpillar setae) confirms histamine-mediated pathophysiology. 1, 2

Disposition and Follow-Up

• Discharge instructions should include avoidance of future caterpillar exposure 3
• Consider prescribing epinephrine auto-injector for patients with severe reactions 8
• Refer to allergy/immunology for potential desensitization if occupational exposure is unavoidable 3
• Document the specific caterpillar species if known, as certain species (processionary caterpillars) are more allergenic 1

Expected Clinical Course

• Most patients show symptom improvement within 90 minutes of treatment initiation 8
• Complete resolution typically occurs within 24-48 hours with appropriate therapy 7
• Tongue and oropharyngeal edema may take longer than 48 hours to fully resolve 7