Clinical Presentation of Allergy

Overview

Severity Spectrum

Gell & Coombs Classification of Hypersensitivity (Clinical Basis)

Clinical Syndromes - Organ by Organ

1. Allergic Rhinitis (Mild end of spectrum)

• Sneezing, nasal congestion, rhinorrhea (clear, watery)
• Nasal pruritus ("allergic salute")
• Post-nasal drip, hyposmia
• Seasonal (pollens) or perennial (dust mites, pet dander, molds)
• Often co-exists with allergic conjunctivitis: bilateral eye itching, redness, tearing, chemosis

2. Allergic Conjunctivitis

• Bilateral itching, redness, watery discharge
• Conjunctival injection and chemosis (swelling)
• Closely associated with allergic rhinitis ("rhinoconjunctivitis")

3. Atopic Dermatitis (Eczema)

• Chronic, relapsing pruritic skin inflammation
• Distribution varies by age: face and extensor surfaces in infants; flexural creases (antecubital, popliteal) in children and adults
• Dry skin (xerosis), lichenification with chronic scratching
• Family history of atopy (asthma, rhinitis, eczema) typically present

4. Urticaria (Hives)

• Raised, erythematous, central wheal with surrounding reflex erythema
• Intensely pruritic or burning sensation
• Individual lesions resolve within 30 minutes to 24 hours (key diagnostic point)
• Triggers: foods, drugs, temperature changes, physical stimuli, insect stings
• Acute urticaria (<6 weeks) vs. chronic urticaria (>6 weeks)

5. Angioedema

• Sudden swelling of the subcutaneous tissue or mucous membranes - deeper than urticaria
• More painful than pruritic (unlike urticaria)
• Slower to resolve than urticaria
• Common sites: lips, tongue, periorbital tissue, larynx, extremities
• Danger sign: laryngeal or tongue involvement can cause airway compromise
• Two mechanisms:
  • Histaminergic (allergic): responds to epinephrine and antihistamines
  • Non-histaminergic: hereditary angioedema (HAE) or ACE inhibitor-induced; does NOT reliably respond to epinephrine/antihistamines

6. Allergic Asthma

• Episodic wheeze, dyspnea, chest tightness, cough (especially nocturnal)
• Triggered by specific allergens (pollens, dust mites, animal dander, molds)
• Reversible airflow obstruction on spirometry
• Eosinophilia in sputum and blood

7. Food Allergy

• Common allergens: peanuts, tree nuts, milk, eggs, shellfish, soy, wheat
• Symptoms typically within minutes to 2 hours of ingestion
• Manifestations: oral allergy syndrome (lip/throat itching), urticaria, vomiting, diarrhea, angioedema, anaphylaxis
• GI symptoms: nausea, cramping, diarrhea, vomiting

Anaphylaxis - The Severe End

System-by-System Clinical Features

Clinical pearl: Skin findings may be absent in up to 20% of anaphylaxis cases, particularly in rapid-onset reactions. Cardiovascular collapse can occur without any skin features.

Common Triggers of Anaphylaxis

• Foods: Peanuts, tree nuts, shellfish, milk, eggs (most common in children)
• Medications: Antibiotics (especially penicillins), NSAIDs, chemotherapy agents
• Insect stings: Hymenoptera (bees, wasps, hornets), fire ants
• Natural rubber latex
• Radiocontrast media (RCM)
• Exercise-induced and idiopathic (no identifiable trigger)

Risk Factors for Severe/Fatal Anaphylaxis

• Poorly controlled asthma
• Concurrent beta-blocker or ACE inhibitor use
• History of mastocytosis
• Delayed epinephrine administration
• Extremes of age

Hypersensitivity by Pattern

Immediate (within minutes)

• Type I IgE-mediated: urticaria, angioedema, anaphylaxis
• Maximal at 15-30 minutes after allergen exposure

Late-Phase Reaction (4-12 hours later)

• Inflammatory cell infiltration (eosinophils, T cells)
• Recurrent or worsening symptoms hours after initial reaction resolved
• Clinically important in asthma and atopic dermatitis

Delayed (24-72 hours)

• Type IV cell-mediated: contact dermatitis, drug hypersensitivity (DRESS, SJS/TEN)
• DRESS syndrome: Drug Rash, Eosinophilia, and Systemic Symptoms - associated with anticonvulsants, allopurinol

Key Diagnostic Clues at the Bedside

1. Timing - symptoms within minutes of exposure suggests IgE-mediated allergy
2. Reproducibility - same symptoms with same trigger on re-exposure
3. Atopic history - personal or family history of eczema, asthma, rhinitis
4. Skin findings - urticaria and angioedema are the hallmark cutaneous signs
5. Multi-system involvement - two or more body systems affected = anaphylaxis until proven otherwise
6. Laboratory: Elevated total/specific IgE, peripheral eosinophilia, serum tryptase (elevated in anaphylaxis, peaks 1-2 hours after onset)

• Rosen's Emergency Medicine, Chapter 106 - Allergy and Anaphylaxis
• Harrison's Principles of Internal Medicine, 22e - Hypersensitivity Pneumonitis
• Jawetz, Melnick & Adelberg's Medical Microbiology, 28e - Hypersensitivity
• Anaphylaxis review (Abrams et al., 2024) - PMID: 39654057