Utricaria vs angioedema vs anaphylaxis

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Urticaria vs Angioedema vs Anaphylaxis

These three conditions exist on a spectrum of allergic/hypersensitivity reactions, sharing common mediators but differing critically in depth of tissue involvement, systemic spread, and life threat.

1. Urticaria (Hives)

Definition

A cutaneous reaction marked by acute onset of pruritic, erythematous wheals of varying size that are classically "fleeting" - individual lesions typically resolve within 24 hours, though new ones may appear. Affects up to 15-20% of the population at some point in their lives.

Pathophysiology

Mast cell and basophil degranulation releases mediators (histamine, bradykinin, kallikrein, acetylcholine) into the superficial dermis, causing localized vasodilation and increased vascular permeability. Can be triggered by:

Immunologic (IgE-mediated): foods (peanuts, shellfish, eggs, tree nuts), drugs (penicillin), latex
Non-immunologic (direct mast cell activation): aspirin, NSAIDs, opioids, physical stimuli (cold, exercise, pressure)
Infections: viral (rhinovirus, hepatitis, EBV, rotavirus), fungal (Candida), parasitic

Clinical Features

Raised, erythematous, pruritic wheals (transient, blanch with pressure)
Individual lesions last <24 hours and move/migrate
Dermographism possible
No systemic involvement (distinguishes from anaphylaxis)

Classification by Duration

Type	Duration
Acute	<6 weeks
Chronic	>6 weeks (more common in women, 40s-50s)

Treatment

Identify and remove the offending agent
H1 antihistamines (first-line; non-sedating preferred)
Add H2 antihistamines (e.g., ranitidine) for severe/chronic/refractory cases
Corticosteroids - evidence suggests adding them to antihistamines may not provide additional benefit over antihistamines alone for relapse prevention
Epinephrine for severe/refractory cases
Omalizumab (anti-IgE) for refractory chronic spontaneous urticaria
Cold compresses for symptomatic relief

2. Angioedema

Definition

A reaction similar to urticaria but involving deeper tissues - edema in the deep dermis, subcutaneous, and submucosal layers, typically affecting the face, lips, tongue, throat, and distal extremities. The deeper location makes it potentially life-threatening due to airway compromise.

Key Difference from Urticaria

Feature	Urticaria	Angioedema
Layer involved	Superficial dermis	Deep dermis + subcutaneous/submucosal
Pruritus	Prominent	Less prominent (more burning/painful)
Appearance	Raised wheals	Diffuse non-pitting swelling
Location	Anywhere	Face, lips, tongue, throat, extremities
Airway risk	No	Yes - can cause fatal obstruction

Types

1. Allergic/IgE-mediated - same mediators as urticaria; responds to epinephrine, antihistamines, steroids

2. ACE inhibitor-induced - accounts for 0.1-0.7% of ACE inhibitor users; caused by accumulation of bradykinin and substance P (not histamine); classically involves tongue and face; can occur years after starting therapy

Responds poorly to antihistamines/steroids/epinephrine
Managed with C1 esterase inhibitor, icatibant (bradykinin B2 receptor antagonist), or ecallantide

3. Hereditary Angioedema (HAE) - rare autosomal dominant; C1 esterase inhibitor deficiency (Type I: low levels; Type II: dysfunctional enzyme). ~25% are new mutations

Attacks involve upper airway, GI tract, extremities; last hours to 1-2 days
Classic antiallergic drugs (epinephrine, antihistamines, steroids) are INEFFECTIVE
Best screening test: C4 level (<30% of normal is suggestive)
Acute treatment: C1-INH concentrate (Berinert 20 U/kg IV), icatibant 30 mg SC, or ecallantide
If C1-INH unavailable: fresh frozen plasma (2-3 units)
Prophylaxis: attenuated androgens (danazol 200 mg TID, stanozolol 2 mg TID)

Management of Angioedema (General)

Airway assessment is the priority - airway can occlude rapidly and unpredictably
For allergic type: epinephrine, antihistamines, corticosteroids
For ACE inhibitor-induced or HAE: target bradykinin pathway (see above)

3. Anaphylaxis

Definition

An acute, severe, potentially fatal systemic hypersensitivity reaction involving multiple organ systems. It is the most dangerous end of the allergic spectrum. Estimated to occur in ~2-5% of the population over a lifetime; fatal in <1% of cases.

Pathophysiology

Massive mast cell/basophil degranulation releases histamine, tryptase, leukotrienes, prostaglandins, and PAF into the systemic circulation, causing:

Widespread vasodilation → hypotension/shock
Increased vascular permeability → angioedema, urticaria
Bronchospasm → respiratory compromise
GI smooth muscle contraction → vomiting, diarrhea

Common Triggers

Foods: peanuts, shellfish, tree nuts, fish, soy, milk, eggs (most common in children)
Medications: beta-lactam antibiotics, NSAIDs, chemotherapeutic agents, contrast media
Insect stings: Hymenoptera venoms
Natural rubber latex
Idiopathic: no trigger found in up to 60% of adults

Diagnostic Criteria (Clinical Diagnosis)

Anaphylaxis is highly likely if any one of these three criteria is met:

Acute illness with skin/mucosal involvement + respiratory compromise OR hypotension/end-organ dysfunction
Two or more systems affected after allergen exposure (skin, respiratory, cardiovascular, GI)
Known allergen exposure + hypotension alone

Signs and Symptoms by System

System	Features (approximate incidence)
Skin/mucosal	Urticaria, flushing, pruritus (80-90%), angioedema
Respiratory	Bronchospasm, laryngeal edema, stridor, hypoxia (50%)
Cardiovascular	Hypotension, tachycardia, shock, arrhythmia
GI	Nausea, vomiting, abdominal cramps, diarrhea
Neurological	Anxiety, syncope, loss of consciousness

Important: skin symptoms may be absent in up to 20% of severe reactions - do not rely on rash to diagnose anaphylaxis.

Timeline

Symptoms typically begin within 60 minutes of exposure (often immediately)
Faster onset = more severe reaction
50% of fatal cases occur within the first hour
Biphasic reaction: occurs in ~4-5% (up to 20% in some reports); second phase peaks 8-11 hours after initial exposure, symptoms manifest 3-4 hours after initial resolution - mediated by leukotrienes

Risk Factors for Severe/Fatal Anaphylaxis

Poorly controlled asthma
Mastocytosis
Concurrent beta-blocker or ACE inhibitor use (beta-blockers worsen response to epinephrine)
Delayed epinephrine administration
Upright posture at onset
Extremes of age

Treatment

First-line - IMMEDIATE:

Epinephrine IM (1 mg/mL), 0.01 mg/kg up to 0.5 mg, into the outer thigh - no absolute contraindications in anaphylaxis; administer immediately
Lay patient supine (upright position at onset increases mortality)
High-flow oxygen
IV access + IV crystalloid bolus for hypotension

Second-line (adjuncts, NOT substitutes for epinephrine):

H1 antihistamines (diphenhydramine)
H2 antihistamines (ranitidine)
Corticosteroids (may reduce biphasic reaction risk, though evidence is limited)
Bronchodilators (salbutamol) for bronchospasm

Refractory/Severe:

IV epinephrine infusion if refractory to repeated IM doses
Vasopressors (dopamine, norepinephrine) for persistent shock
Glucagon for patients on beta-blockers (reverses beta-blockade)

Observation: All patients require monitoring for biphasic reaction (minimum 4-6 hours observation for moderate reactions; 24 hours for severe).

Discharge: Prescribe epinephrine autoinjector and allergy follow-up.

Side-by-Side Comparison

Feature	Urticaria	Angioedema	Anaphylaxis
Tissue layer	Superficial dermis	Deep dermis/subcutaneous	Systemic (multiorgan)
Primary lesion	Wheals/hives	Diffuse non-pitting swelling	Variable (may include both above)
Pruritus	Prominent	Mild/burning	Variable
Airway risk	None	Yes (tongue, larynx)	High (laryngeal edema + bronchospasm)
Systemic involvement	No	No (unless HAE with GI)	Yes (defining feature)
Life-threatening	Rarely	Potentially (airway)	Yes
First-line treatment	H1 antihistamine	Airway + epinephrine (allergic) OR bradykinin antagonists (HAE/ACEI)	Epinephrine IM - IMMEDIATELY
Steroid use	Yes (adjunct)	Ineffective in HAE	Adjunct (second-line)
Epinephrine role	Severe/refractory only	Allergic type only	Mandatory first-line

Key Clinical Pearls

Urticaria + angioedema can occur together and may be the first signs of developing anaphylaxis - monitor closely
HAE does not respond to epinephrine, antihistamines, or steroids - this is a critical distinction in the ED
ACE inhibitor angioedema can be delayed by years after starting the drug and requires stopping the ACE inhibitor permanently
The absence of skin findings does not rule out anaphylaxis (20% of severe cases lack skin manifestations)
Beta-blockers blunt the response to epinephrine in anaphylaxis - these patients may need glucagon and higher epinephrine doses
Serum tryptase (elevated for several hours post-reaction) can confirm anaphylaxis retrospectively but has poor sensitivity (~1/3 are normal

Sources: ROSEN's Emergency Medicine, Tintinalli's Emergency Medicine, Andrews' Diseases of the Skin - all cited from the medical textbook library.

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