Urticaria Disease Background

Introduction

Urticaria is a predominantly mast cell-driven disease characterized by the appearance of wheals (hives) and/or angioedema. 

Epidemiology

Urticaria can occur at any age and affects 1% of the global population. There is an increased incidence noted in atopic patients. Globally, children <5 years showed the highest prevalence rates which progressively declines as age increases.  There is higher morbidity of urticaria in lower income regions due to the increased burden of infectious diseases and environmental pollution.  

Latin America and Asia showed higher point prevalence of chronic urticaria than other regions. Across most age groups, women are more affected than men.  However, the same incidence rates are noted in both genders in the elderly. Chronic urticaria is more prevalent in Asia compared to Europe and North America. 

Pathophysiology

Urticaria involves the activation of mast cells and basophils leading to the release of vasoactive mediators (eg histamine, leukotrienes, prostaglandins) and localized capillary vasodilation. Wheals in urticaria involve the upper and mid-dermis and are characterized by variable shape and size surrounded by erythema, pruritus, or burning sensation, with a transient appearance (skin returns to normal within 30 minutes to 24 hours). Angioedema in urticaria features sudden prolonged swelling of the lower dermis and subcutis or mucous membranes, produces pain or discomfort, and has a slower resolution compared to wheals (up to 72 hours). The intensity of pruritus of urticaria varies but may be severe enough to disrupt sleep, work or school.

Etiology

Specific causes of urticaria are more likely to be identified in acute cases but approximately 50% of patients with acute urticaria are diagnosed with idiopathic urticaria. It can be triggered by immunological or non-immunological mechanisms (eg Indomethacin, opiates, radiocontrast material, berries, shellfish).  


Acute Urticaria  

Causes include the following:

• Food allergies: Shellfish, tree nuts, milk, eggs, legumes
• Medication allergies: Aspirin, hormone therapy, Penicillin, sulfonamides
• Insect sting allergies: Hymenoptera, honeybee, fire ant
• Infections: Chronic bacterial infections, viral upper respiratory infections, hepatitis B and C, fungal infections, helminthic
• Systemic diseases: Autoimmune thyroid disease, cryoglobulinemia, cutaneous mastocytosis, serum sickness, systemic lupus erythematosus
• Immunologic contact urticaria: Benzoic acid, Salicylic acid, parabens, natural rubber latex, nickel
• Non-immunologic contact urticaria: Caterpillars, plants
• Others: Emotional stress, pregnancy, malignancy (eg lymphomas, endocrine tumors), pemphigoid, hair bleaches, saliva

Chronic Urticaria  

An autoimmune component may be found in up to 50% of patients with chronic urticaria. A patient can have >1 form of chronic urticaria, including >1 form of chronic inducible urticaria and chronic spontaneous urticaria.  

Chronic Spontaneous Urticaria  

Its known causes include autoimmunity type I (autoallergic) with IgE autoantibodies to self-antigens and autoimmunity type IIb with mast cell-directed activating autoantibodies. The patient has high levels of proinflammatory cytokines (eg interleukin [IL]-17, IL-31, IL-33).  

Chronic Inducible Urticaria


The known causes are the following:

• Cold urticaria
• Delayed pressure urticaria
• Heat urticaria
• Symptomatic dermographism (daily lesions and recurrent episodic lesions are not differentiated)
• Solar urticaria
• Vibratory angioedema
• Aquagenic urticaria
• Cholinergic urticaria
• Contact urticaria

Classification

Urticaria is classified as acute or chronic, and as spontaneous (no definite triggering factor) or inducible (a specific definite triggering factor is identified).  

Acute Urticaria  

Acute urticaria lesions occur ≤6 weeks in duration and are usually without angioedema. It is more common in children and young adults and tends to have a triggering event.

Urticaria_Disease Background