Chronic spontaneous urticaria (CSU) is defined as the spontaneous appearance of wheals, angioedema, or both for more than 6 weeks.1,2 Unlike chronic inducible urticaria, CSU symptoms cannot be induced through provocation tests and are independent of environmental conditions and allergens. Visually, symptoms cannot be distinguished from other causes of urticaria or angioedema, making a detailed patient history crucial for diagnosis.
Signs and Symptoms
Patients with CSU will experience unexplained, pruritic hives called wheals. These wheals typically appear for less than 24 hours in one area before fading and reappearing in a different area of the body. Episodes of wheals appearing sporadically and seemingly at random can persist for several days.1 The associated pruritus can be severe and even disabling, leading some to refer to the condition as "the devil's itch."3 Though wheals present more frequently, 43% to 59% of patients will also experience angioedema.4 This swelling can last up to 48 hours. Roughly 10% of patients with CSU present with angioedema as their primary symptom.3
Pathophysiology
CSU is primarily mediated by dermal mast cells.5 These mast cells degranulate, triggering histamine-facilitated vasodilation and increased vascular permeability that manifests clinically as pruritic wheals or angioedema.5 The exact mechanism triggering this initial mast cell degranulation remains unclear.5 Three subtypes of CSU exist: type I (autoallergic, immunoglobulin [Ig]E mediated), type IIb (autoimmune, IgG autoantibody-mediated), and cause unknown.4,6 Type IIb is believed to cause higher disease activity than type I, but the utility of these subtypes in predicting treatment response or symptom burden is unclear (Figure 1).4
Burden of CSU Disease in the United States
An estimated 500,000 people suffer from chronic urticaria of any etiology, but the true figure is likely higher.7 When CSU
Signs and Symptoms
Patients with CSU will experience unexplained, pruritic hives called wheals. These wheals typically appear for less than 24 hours in one area before fading and reappearing in a different area of the body. Episodes of wheals appearing sporadically and seemingly at random can persist for several days.1 The associated pruritus can be severe and even disabling, leading some to refer to the condition as "the devil's itch."3 Though wheals present more frequently, 43% to 59% of patients will also experience angioedema.4 This swelling can last up to 48 hours. Roughly 10% of patients with CSU present with angioedema as their primary symptom.3
Pathophysiology
CSU is primarily mediated by dermal mast cells.5 These mast cells degranulate, triggering histamine-facilitated vasodilation and increased vascular permeability that manifests clinically as pruritic wheals or angioedema.5 The exact mechanism triggering this initial mast cell degranulation remains unclear.5 Three subtypes of CSU exist: type I (autoallergic, immunoglobulin [Ig]E mediated), type IIb (autoimmune, IgG autoantibody-mediated), and cause unknown.4,6 Type IIb is believed to cause higher disease activity than type I, but the utility of these subtypes in predicting treatment response or symptom burden is unclear (Figure 1).4
Burden of CSU Disease in the United States
An estimated 500,000 people suffer from chronic urticaria of any etiology, but the true figure is likely higher.7 When CSU
