Pruritus

Introduction

Pruritus, commonly known as itching, is a frequent complaint in dermatology and general practice. Understanding its causes, evaluation, and management is crucial for success in the MCCQE1 exam and future medical practice in Canada. This comprehensive guide will cover key aspects of pruritus, tailored to the Canadian healthcare context and MCCQE1 preparation.

Epidemiology in the Canadian Context

• Prevalence: Approximately 8-10% of the Canadian population experiences chronic pruritus
• Higher incidence in:
  • Elderly populations (15-20% of Canadians over 65)
  • Patients with chronic kidney disease (up to 40% of Canadian dialysis patients)
  • Individuals with certain ethnic backgrounds (e.g., higher rates in Indigenous populations)

Pathophysiology

Understanding the mechanisms of pruritus is essential for MCCQE1 success:

1. Neurophysiology:

   • Itch signals are transmitted via C-fibers in the dorsal root ganglia
   • Spinal cord processing involves the spinothalamic tract
   • Central processing occurs in the somatosensory cortex

2. Mediators:

   • Histamine (classic itch mediator)
   • Substance P
   • Cytokines (e.g., IL-31)
   • Opioids (important in chronic kidney disease-associated pruritus)

Etiology and Classification

For MCCQE1 preparation, categorize pruritus into four main types:

1. Dermatological
2. Systemic
3. Neurological
4. Psychogenic

Dermatological Causes

Common skin conditions causing pruritus in Canada:

• Atopic dermatitis (eczema)
• Psoriasis
• Contact dermatitis
• Urticaria
• Scabies

Systemic Causes

Important for MCCQE1: Be aware of systemic diseases that can present with pruritus:

Neurological Causes

• Multiple sclerosis
• Brain tumors
• Neuropathic itch (e.g., post-herpetic neuralgia)

Psychogenic Causes

• Depression
• Anxiety disorders
• Obsessive-compulsive disorder

Clinical Evaluation

Management

Treatment approach in the Canadian healthcare system:

1. Identify and treat underlying cause
2. Symptomatic relief
3. Patient education and lifestyle modifications

Topical Treatments

• Emollients and moisturizers
• Topical corticosteroids
• Topical calcineurin inhibitors (e.g., tacrolimus, pimecrolimus)
• Local anesthetics (e.g., pramoxine)

Systemic Treatments

• Antihistamines (first and second-generation)
• Gabapentin or pregabalin for neuropathic itch
• Antidepressants (e.g., sertraline, mirtazapine) for psychogenic pruritus
• UV phototherapy (commonly used in Canadian dermatology practices)

Canadian Guidelines

The Canadian Dermatology Association provides guidelines for managing pruritus:

1. Emphasize the importance of proper skin care and avoiding irritants
2. Recommend short, lukewarm showers and pat-drying the skin
3. Advise the use of fragrance-free, hypoallergenic moisturizers
4. Suggest cool compresses or colloidal oatmeal baths for symptomatic relief
5. Encourage patients to keep nails short to minimize skin damage from scratching

Key Points to Remember for MCCQE1

• Pruritus can be a manifestation of various dermatological and systemic diseases
• Always consider underlying systemic causes, especially in generalized pruritus without rash
• Chronic kidney disease is a common cause of pruritus in Canada, affecting up to 40% of dialysis patients
• First-line treatment often includes topical therapies and antihistamines
• Canadian guidelines emphasize skin care and lifestyle modifications as essential components of management
• Be familiar with the CanMEDS roles, especially the "Medical Expert" and "Communicator" roles, when approaching pruritus cases

Sample Question

# Sample Question

A 62-year-old woman presents to her family physician in Toronto with a 3-month history of generalized pruritus. She reports that the itching is worse at night and is not associated with any visible rash. Her medical history includes hypertension and type 2 diabetes mellitus. Physical examination reveals dry skin and excoriations on her arms and legs. Which one of the following investigations is most appropriate to perform next?

- [ ] A. Skin biopsy
- [ ] B. Serum IgE levels
- [ ] C. Liver function tests
- [ ] D. Chest X-ray
- [ ] E. Patch testing

Explanation

The correct answer is:

• C. Liver function tests

Explanation: This patient presents with generalized pruritus without a primary rash, which raises suspicion for an underlying systemic cause. Given her age and the absence of a clear dermatological etiology, it's important to investigate common systemic causes of pruritus. Liver function tests are an appropriate next step to evaluate for hepatobiliary causes of pruritus, such as cholestatic liver disease or primary biliary cholangitis, which can present with generalized itching as an early symptom.

Other options: A. Skin biopsy is not indicated as there is no primary skin lesion. B. Serum IgE levels are more relevant for allergic conditions, which are less likely given the presentation. D. Chest X-ray could be considered if malignancy is suspected, but it's not the most appropriate first-line test. E. Patch testing is used to diagnose contact dermatitis, which is unlikely given the generalized nature of the pruritus and absence of a rash.

This question tests the candidate's ability to prioritize investigations based on the clinical presentation, aligning with the CanMEDS Medical Expert role.

References

1. Canadian Dermatology Association. (2021). Position Statement on the Management of Chronic Pruritus. https://dermatology.ca/guidelines/ (opens in a new tab)

2. Yosipovitch, G., & Bernhard, J. D. (2013). Chronic Pruritus. New England Journal of Medicine, 368(17), 1625-1634.

3. Medical Council of Canada. (2023). Objectives for the Qualifying Examination. https://mcc.ca/objectives/ (opens in a new tab)

4. Patel, T., & Yosipovitch, G. (2010). Therapy of Pruritus. Expert Opinion on Pharmacotherapy, 11(10), 1673-1682.

5. Canadian Medical Association. (2023). CanMEDS Framework. https://www.royalcollege.ca/rcsite/canmeds/canmeds-framework-e (opens in a new tab)