Urticaria

Introduction | Aetiology and Risk Factors | Clinical Presentation | Diagnosis | Management and Treatment | When to Refer | References

Introduction

Urticaria, commonly known as hives, is a skin condition characterised by the sudden appearance of raised, red, itchy welts (wheals) on the skin. These welts can vary in size and may merge to form larger areas of swelling. Urticaria can be acute, lasting less than six weeks, or chronic, persisting for more than six weeks. While it is often self-limiting, chronic urticaria can significantly impact a patient’s quality of life. Urticaria can be triggered by various factors, including allergens, infections, and stress.

Aetiology and Risk Factors

Urticaria results from the release of histamine and other inflammatory mediators from mast cells in the skin. The triggers can vary widely, and in many cases, the exact cause may remain unidentified. Key factors include:

• Allergens: Common triggers include foods (e.g., nuts, shellfish), medications (e.g., antibiotics, NSAIDs), insect stings, and environmental factors (e.g., pollen, animal dander).
• Infections: Viral, bacterial, or fungal infections can trigger acute urticaria. Common culprits include upper respiratory tract infections and gastrointestinal infections.
• Physical Triggers: Physical urticaria can be triggered by stimuli such as pressure (dermographism), cold, heat, sunlight, or exercise.
• Stress: Psychological stress is a known exacerbating factor for urticaria, particularly chronic cases.
• Autoimmune Diseases: Chronic urticaria is sometimes associated with autoimmune conditions such as thyroid disease, lupus, or rheumatoid arthritis.
• Idiopathic: In many cases of chronic urticaria, no specific cause can be identified, and it is termed chronic idiopathic urticaria.

Clinical Presentation

Urticaria presents with the following features:

• Wheals (Hives): The primary lesion in urticaria is a wheal, which is a raised, red or pale, itchy area of swelling. Wheals may be small (a few millimetres) or large (several centimetres) and can appear anywhere on the body.
• Itching: Intense itching is a hallmark of urticaria and can be distressing for the patient.
• Transient Nature: Individual wheals typically last less than 24 hours, resolving without leaving marks, but new lesions may continue to appear.
• Angioedema: In some cases, urticaria may be accompanied by angioedema, which is deeper swelling that often affects the lips, eyelids, or throat. Angioedema may cause pain or a burning sensation and can be life-threatening if it involves the airway.
• Chronic Urticaria: Chronic urticaria is defined by the presence of hives most days of the week for six weeks or longer. The underlying cause is often difficult to identify.

Diagnosis

The diagnosis of urticaria is primarily clinical, based on the characteristic appearance of the lesions and patient history:

• History: Take a detailed history, including the onset, duration, and pattern of the hives, potential triggers, recent infections, medications, and any associated symptoms such as angioedema or difficulty breathing.
• Physical Examination: Examine the skin for typical wheals and any signs of angioedema. Check for any systemic signs that might suggest an underlying cause.
• Laboratory Tests: In acute urticaria, laboratory tests are usually not necessary unless an underlying cause is suspected. In chronic cases, tests may include a complete blood count (FBC), thyroid function tests, and autoimmune markers to rule out associated conditions.
• Allergy Testing: In cases where a specific allergen is suspected, referral for allergy testing (e.g., skin prick tests or specific IgE blood tests) may be considered.
• Challenge Tests: For physical urticarias, specific challenge tests (e.g., ice cube test for cold urticaria) can help confirm the diagnosis.

Management and Treatment

Management of urticaria focuses on symptom relief, identification and avoidance of triggers, and treatment of any underlying causes:

1. Antihistamines

• Non-Sedating Antihistamines: First-line treatment for urticaria includes non-sedating antihistamines such as cetirizine, loratadine, or fexofenadine. These medications block histamine receptors and reduce itching and wheal formation. They are typically taken once daily, with the dose increased if necessary.
• Sedating Antihistamines: In cases of severe itching or when symptoms are interfering with sleep, sedating antihistamines like chlorphenamine may be used, particularly at night.
• Chronic Urticaria: For chronic cases, antihistamines may need to be continued long-term, and doses can be increased up to four times the standard dose under specialist guidance.

2. Second-Line Treatments

• H₂ Antagonists: Medications such as ranitidine may be added to the treatment regimen to block histamine receptors in the stomach, which can help control more severe cases.
• Leukotriene Receptor Antagonists: Drugs like montelukast can be used as adjunctive therapy in patients who do not respond adequately to antihistamines alone.
• Short Courses of Oral Corticosteroids: Prednisolone may be used for a short duration (typically 3-5 days) in cases of severe acute urticaria or angioedema, but long-term use is generally avoided due to potential side effects.
• Omalizumab: An anti-IgE monoclonal antibody, omalizumab is used for chronic urticaria that is refractory to antihistamines. It is administered as a subcutaneous injection, typically once a month.

3. Lifestyle and Supportive Care

• Avoidance of Triggers: Patients should be advised to avoid known triggers, such as specific foods, medications, or environmental factors that may precipitate urticaria.
• Stress Management: Since stress can exacerbate urticaria, stress-reduction techniques such as mindfulness, relaxation exercises, and counselling may be beneficial.
• Skin Care: Recommend the use of gentle, fragrance-free skin care products to reduce the risk of irritation. Cool compresses and calamine lotion may provide symptomatic relief.

4. Emergency Care

• Angioedema or Anaphylaxis: Patients with urticaria who develop signs of angioedema or anaphylaxis (e.g., swelling of the throat, difficulty breathing, dizziness) require emergency medical attention. Administer adrenaline, antihistamines, and corticosteroids as appropriate, and arrange for immediate transfer to an emergency department.

When to Refer

Referral to a specialist, such as a dermatologist or allergist, may be necessary in the following situations:

• Chronic Urticaria: Patients with chronic urticaria that does not respond to standard treatment should be referred for further evaluation and management, including consideration of advanced therapies like omalizumab.
• Refractory Urticaria: If symptoms persist despite high-dose antihistamines and other second-line treatments, referral to a specialist is advised.
• Diagnostic Uncertainty: If there is uncertainty about the diagnosis or concern for an underlying systemic condition, a referral for further investigation is warranted.
• Angioedema: Patients with recurrent or severe angioedema should be referred for specialist assessment, particularly if it occurs without urticaria or in association with other systemic symptoms.

References

1. British Association of Dermatologists (2024) Guidelines for the Management of Urticaria. Available at: https://www.bad.org.uk (Accessed: 26 August 2024).
2. National Institute for Health and Care Excellence (2024) Urticaria: Diagnosis and Management. Available at: https://www.nice.org.uk/guidance/ng100 (Accessed: 26 August 2024).
3. British National Formulary (2024) Antihistamines and Other Treatments for Urticaria. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).