Urticaria Angioedema

Introduction

Welcome to the comprehensive MCCQE1 study guide on Urticaria and Angioedema. This resource is tailored for Canadian medical students preparing for the Medical Council of Canada Qualifying Examination Part I (MCCQE1). Understanding urticaria and angioedema is crucial for success in the MCCQE1 and for your future practice in the Canadian healthcare system.

Definition and Pathophysiology

Urticaria and angioedema are related conditions characterized by localized swelling of the skin and mucous membranes.

• Urticaria (hives): Pruritic, erythematous, raised wheals on the skin that blanch with pressure
• Angioedema: Deeper swelling of the dermis and subcutaneous or submucosal tissues

Both conditions result from the release of histamine and other inflammatory mediators from mast cells and basophils.

Epidemiology in Canada

Understanding the prevalence and impact of urticaria and angioedema in Canada is essential for MCCQE1 preparation:

• Lifetime prevalence of urticaria in Canada: approximately 15-25% of the population
• Chronic urticaria affects about 1% of Canadians
• Angioedema occurs in about 50% of patients with chronic urticaria

Classification

For MCCQE1 preparation, it's crucial to understand the classification of urticaria and angioedema:

1. Acute Urticaria: Duration <6 weeks

2. Chronic Urticaria: Duration ≥6 weeks

   • Chronic Spontaneous Urticaria (CSU)
   • Chronic Inducible Urticaria (CIndU)

3. Angioedema:

   • Associated with urticaria
   • Without urticaria (e.g., hereditary angioedema)

Etiology

Understanding the causes of urticaria and angioedema is key for MCCQE1 success:

Clinical Presentation

For the MCCQE1 exam, focus on recognizing key clinical features:

Urticaria

• Pruritic, erythematous wheals
• Individual lesions last <24 hours
• Can occur anywhere on the body

Angioedema

• Swelling of deeper tissues (lips, eyelids, genitals)
• Often painful or burning sensation
• Can affect airways (potential emergency)

Diagnosis

Accurate diagnosis is crucial for MCCQE1 success and future practice in Canada:

1. History: Detailed history of triggers, duration, associated symptoms

2. Physical Examination: Assess lesions, look for signs of systemic involvement

3. Laboratory Tests:

   • CBC with differential
   • ESR/CRP
   • Thyroid function tests
   • Consider specific IgE testing if food allergy suspected

4. Special Considerations:

   • C4 and C1 esterase inhibitor levels for suspected hereditary angioedema

Management

Understanding the management of urticaria and angioedema is crucial for MCCQE1 success and aligns with the CanMEDS roles of Medical Expert and Health Advocate:

First-line Treatment

1. H1 Antihistamines:
   • Second-generation (non-sedating): Cetirizine, Loratadine, Desloratadine
   • Can increase dose up to 4x the standard dose if needed

Second-line Treatment

2. H2 Antihistamines: Ranitidine, Famotidine
3. Leukotriene Receptor Antagonists: Montelukast

Third-line Treatment

4. Omalizumab: For chronic spontaneous urticaria refractory to high-dose antihistamines

Acute Management

5. Corticosteroids: Short course for severe acute episodes
6. Epinephrine: For anaphylaxis or severe angioedema affecting airways

Canadian Guidelines

The Canadian Society of Allergy and Clinical Immunology (CSACI) provides guidelines for managing urticaria and angioedema in Canada. Key points for MCCQE1 preparation include:

1. Emphasis on non-sedating antihistamines as first-line treatment
2. Recommendation to avoid routine extensive testing in chronic spontaneous urticaria
3. Guidance on step-up therapy for refractory cases
4. Specific recommendations for managing hereditary angioedema in Canada

Key Points to Remember for MCCQE1

• Urticaria and angioedema can occur separately or together
• Chronic urticaria is defined as lasting ≥6 weeks
• Second-generation antihistamines are the mainstay of treatment in Canada
• Hereditary angioedema requires specific diagnosis and management
• Angioedema affecting airways is a medical emergency
• Canadian guidelines emphasize step-wise approach to management
• Omalizumab is approved in Canada for chronic spontaneous urticaria refractory to antihistamines

Sample Question

# Sample Question

A 35-year-old woman presents to her family physician with a 2-month history of recurrent, pruritic wheals on her trunk and extremities. The wheals typically last for a few hours before resolving without leaving any marks. She denies any known triggers and has no significant past medical history. Which one of the following is the most appropriate first-line treatment for this patient?

- [ ] A. Oral prednisone
- [ ] B. Topical corticosteroids
- [ ] C. Cetirizine
- [ ] D. Omalizumab
- [ ] E. Montelukast

Explanation

The correct answer is:

• C. Cetirizine

This patient presents with symptoms consistent with chronic spontaneous urticaria (CSU), given the duration of symptoms (>6 weeks) and the lack of identifiable triggers. According to Canadian guidelines and MCCQE1 objectives:

1. Cetirizine, a second-generation antihistamine, is the first-line treatment for CSU in Canada.
2. Oral prednisone is not recommended for long-term management of CSU and should be reserved for short courses in severe acute episodes.
3. Topical corticosteroids are not effective for widespread urticaria.
4. Omalizumab is a third-line treatment in Canada, used when high-dose antihistamines fail.
5. Montelukast is considered a second-line or add-on therapy, not a first-line treatment.

Remember for the MCCQE1: Always consider second-generation antihistamines as the initial treatment for chronic urticaria in the Canadian healthcare context.

References

1. Kanani, A., Schellenberg, R., & Warrington, R. (2011). Urticaria and angioedema. Allergy, Asthma & Clinical Immunology, 7(1), S9.

2. Sussman, G., Hébert, J., Barron, C., Bian, J., Caron-Guay, R. M., Laflamme, S., & Stern, S. (2014). Real-life experiences with omalizumab for the treatment of chronic urticaria. Annals of Allergy, Asthma & Immunology, 112(2), 170-174.

3. Zuberbier, T., Aberer, W., Asero, R., Abdul Latiff, A. H., Baker, D., Ballmer-Weber, B., ... & Maurer, M. (2018). The EAACI/GA²LEN/EDF/WAO guideline for the definition, classification, diagnosis and management of urticaria. Allergy, 73(7), 1393-1414.

4. Canadian Society of Allergy and Clinical Immunology. (2020). Position statement on the diagnosis and management of chronic urticaria. Retrieved from https://csaci.ca/position-statements-working-guidelines/ (opens in a new tab)

5. Betschel, S., Badiou, J., Binkley, K., Hébert, J., Kanani, A., Keith, P., ... & Waserman, S. (2019). The International/Canadian Hereditary Angioedema Guideline. Allergy, Asthma & Clinical Immunology, 15(1), 72.