About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
The Bottom Line
- The first decision is whether this is anaphylaxis or airway angioedema: respiratory, cardiovascular, tongue, laryngeal, or rapidly progressive symptoms need emergency treatment
- Urticarial wheals are transient and usually last less than 24 hours in one location; fixed painful purpura suggests urticarial vasculitis instead
- Acute urticaria is commonly idiopathic, viral, drug-related, food-related, insect-related, or physical; extensive testing is rarely useful without a clear trigger
- Chronic spontaneous urticaria is treated stepwise with second-generation non-sedating antihistamines, up-dosing when needed, and specialist therapies for refractory disease
- Angioedema without urticaria suggests bradykinin-mediated disease such as ACE inhibitor angioedema or hereditary angioedema; antihistamines and epinephrine may be less effective
Approach to the Presentation
Urticaria presents with pruritic, raised, transient wheals; angioedema is deeper swelling of dermis, subcutaneous tissue, or mucosa and may be painful rather than itchy. The first MCCQE1 branch point is safety: assess airway, breathing, circulation, voice change, tongue swelling, stridor, wheeze, hypotension, syncope, vomiting, and exposure timing. Histamine-mediated urticaria/angioedema often has wheals and itch and responds to antihistamines and epinephrine when anaphylaxis is present. Bradykinin-mediated angioedema tends to lack wheals and itch, develops more slowly, and may involve abdominal pain or laryngeal swelling. Chronic urticaria is defined by recurrent symptoms for 6 weeks or more and is often spontaneous rather than allergic.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Anaphylaxis | must-not-miss | Acute urticaria/angioedema with respiratory compromise, hypotension, syncope, persistent GI symptoms, or exposure to food/drug/venom/latex | Clinical diagnosis; treat immediately with IM epinephrine |
| Airway Angioedema | must-not-miss | Tongue, floor-of-mouth, uvular or laryngeal swelling, voice change, dysphagia, drooling, stridor, rapidly progressive swelling | Clinical airway assessment; early anesthesia/ENT/ED escalation |
| ACE Inhibitor Angioedema | must-not-miss | Angioedema without wheals or itch, involving lips/tongue/airway; can occur after years on ACE inhibitor; higher risk with previous episodes | Medication history; diagnosis is clinical. Stop ACE inhibitor permanently |
| Hereditary Angioedema | must-not-miss | Recurrent angioedema without urticaria, abdominal pain attacks, laryngeal episodes, family history, onset in childhood/adolescence, triggers include trauma or dental work | C4 level, C1 inhibitor quantity and function; specialist confirmation |
| Acute Spontaneous or Viral Urticaria | common | Sudden itchy wheals lasting less than 6 weeks, often after viral illness; no consistent external trigger | Clinical diagnosis; no routine testing if otherwise well |
| Food-, Drug-, or Venom-Triggered Urticaria | common | Symptoms within minutes to hours of exposure; may recur reproducibly; NSAIDs, antibiotics, opioids, radiocontrast, foods, stings | Detailed exposure history; allergy referral/testing if anaphylaxis or clear reproducible trigger |
| Chronic Spontaneous Urticaria | common | Recurrent wheals, angioedema, or both for more than 6 weeks; often no external allergen; major quality-of-life impact | Clinical diagnosis; limited labs if atypical or systemic symptoms |
| Physical/Inducible Urticaria | common | Triggered by pressure, cold, heat, vibration, exercise, cholinergic sweating, or dermatographism | Provocation testing when safe and clinically needed |
| Serum Sickness-Like Reaction | less common | Urticarial or morbilliform rash with fever, arthralgias, lymphadenopathy after drugs or infection; lesions may persist longer | Clinical diagnosis; CBC, urinalysis, complement if true serum sickness suspected |
| Urticarial Vasculitis | less common | Painful/burning wheals lasting >24 hours in same location, residual bruising or hyperpigmentation, systemic symptoms, arthralgia | Skin biopsy; ESR/CRP, complement, urinalysis as indicated |
| Mastocytosis / Mast Cell Activation | rare | Recurrent flushing, urticaria pigmentosa, anaphylaxis, abdominal symptoms, symptoms triggered by heat/alcohol/NSAIDs | Serum tryptase, dermatology/allergy referral, biopsy if cutaneous disease suspected |
Red Flags & Key History
Symptoms
Wheeze, dyspnea, stridor, throat tightness, hoarseness, tongue swelling, drooling, or dysphagia
Hypotension, syncope, collapse, confusion, or persistent vomiting after exposure
Angioedema without urticaria, especially on ACE inhibitor or with family history
Abdominal pain attacks with swelling episodes — hereditary angioedema clue
Fixed painful lesions lasting more than 24 hours or leaving bruising — urticarial vasculitis
Recent food, medication, insect sting, latex, exercise, alcohol, NSAID, opioid, or radiocontrast exposure
Symptoms provoked by cold, pressure, heat, sweating, or vibration
Signs
Stridor, voice change, tongue/floor-of-mouth swelling
Hypotension, tachycardia, wheeze, hypoxia
Dermatographism or wheals that migrate within hours
Purpura, residual hyperpigmentation, or non-blanching lesions
Absence of wheals in recurrent angioedema
Approach to Investigation
First-line
Clinical diagnosis and airway assessmentDo not delay treatment of anaphylaxis or airway angioedema for lab tests. Assess voice, tongue, uvula, respiratory status, BP, and progression
Exposure and medication historyFood, medication, insect sting, latex, exercise, NSAIDs, opioids, radiocontrast, ACE inhibitors, supplements, infections, and timing relative to symptoms
No routine testing for uncomplicated acute urticariaTesting should be guided by history. Broad allergy panels are low yield and may create false positives
Tryptase when anaphylaxis diagnosis is uncertainObtain acutely and compare with baseline when available; treatment should not wait for the result
Second-line
C4 and C1 inhibitor level/functionFor recurrent angioedema without urticaria, family history, abdominal attacks, or suspected hereditary/acquired angioedema
Limited chronic urticaria labsCBC, ESR/CRP, TSH or other tests only when chronic disease, systemic symptoms, or atypical features exist
Skin biopsyIf urticarial vasculitis suspected: fixed lesions >24 hours, pain/burning, purpura, systemic features
Specialist
Allergy/immunology referralAfter anaphylaxis, suspected hereditary angioedema, recurrent angioedema without wheals, refractory chronic urticaria, or unclear high-risk trigger
ENT/anesthesia/critical careEarly for progressive tongue, floor-of-mouth, laryngeal, or airway angioedema
Management Principles
MCC Urticaria/Angioedema objective + Canadian Dermatology Association resources1
Anaphylaxis or airway threat
- Give IM epinephrine promptly for anaphylaxis; repeat if needed
- Call for help, place patient supine if tolerated, give oxygen, IV fluids for hypotension, bronchodilator for bronchospasm, and monitor closely
- Prepare for early airway management if tongue/laryngeal swelling, voice change, stridor, or rapid progression exists
2
Acute urticaria without anaphylaxis
- Second-generation non-sedating antihistamine is first-line
- Avoid identified triggers, NSAIDs/alcohol if they worsen symptoms, and unnecessary broad testing
- Short course systemic corticosteroid may be considered for severe refractory flares, but is not routine for mild disease
3
Chronic spontaneous urticaria
- Daily second-generation non-sedating antihistamine; increase dose under clinician guidance if inadequate control
- Avoid sedating antihistamines as routine long-term therapy when safer non-sedating options are available
- Refer for specialist therapies such as omalizumab or immunomodulatory treatment when refractory
4
Bradykinin-mediated angioedema
- Stop ACE inhibitor permanently and document adverse reaction; do not re-challenge
- Hereditary angioedema requires specialist-directed on-demand therapy and prophylaxis planning
- Airway protection is the priority because antihistamines, corticosteroids, and epinephrine may be less effective than in histamine-mediated disease
Complications & Pitfalls
- Delaying epinephrine: Antihistamines do not treat airway or shock in anaphylaxis.
- Missing ACE inhibitor angioedema: It can occur after years of uneventful use and often lacks itch or hives.
- Calling fixed purpuric lesions urticaria: Urticarial vasculitis lesions last longer than 24 hours and may bruise.
- Ordering indiscriminate allergy panels: These create false positives unless guided by a convincing history.
- No discharge safety plan after anaphylaxis: Patients need trigger avoidance, epinephrine auto-injector planning, education, and allergy follow-up.
MCCQE1 Exam Tips
- 1Urticaria plus respiratory or cardiovascular compromise = anaphylaxis; IM epinephrine is the next best step
- 2Antihistamines are adjunctive in anaphylaxis; they are not life-saving treatment
- 3Angioedema without wheals points to bradykinin-mediated causes: ACE inhibitor or hereditary angioedema
- 4Hereditary angioedema clues: recurrent swelling, abdominal pain, family history, low C4
- 5Wheals that move and resolve within 24 hours are typical urticaria; fixed painful lesions that bruise suggest vasculitis
- 6Chronic spontaneous urticaria is usually not a food allergy; the MCC answer is stepwise antihistamine therapy, not broad food panels
- 7ACE inhibitor angioedema requires permanent discontinuation even if the medication was started years ago
practicetest your knowledge on urticaria & angioedemaApply what you've learnt with MCCQE1-style questions from the iatroX Q-Bank — dermatologic and beyond.
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Urticaria & Angioedema: guidance by region
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