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What are the causes of chronic urticaria ?

According to the latest research, chronic spontaneous urticaria is explained by one of two main autoimmunity mechanisms: type I and type IIb. Some patients suffer from type I, some from type IIb and some from both. Manifestations of both types are similar, but disease progression, clinical features, and response to different treatments may vary. There are currently new treatments in development that specifically target both types.

Type I

Type I, also called autoallergic, is by far the most common - it represents about 90% of patients. It is characterized by autoantibodies of the Immunoglobulin E (IgE) type. Antibodies against thyroid peroxidase (TPO) are for example common. These antibodies are also implicated in Hashimoto's thyroiditis, the most common cause of hypothyroidism. That would explain why it's common to have both hypothyroidism and chronic hives.

Patients with type I would be more likely to present with another autoimmune disease such as Hashimoto's disease or atopic dermatitis. They also usually have a very good response to treatment with omalizumab (Xolair).

Type IIb

Type IIb is characterized by the presence of Immunoglobulin G (IgG) type autoantibodies against a receptor involved in allergic reactions called FCER1. The diagnosis of type IIb is made by the autologous serum skin test (ASST). A typical patient is an adult female with severe disease, one or more autoimmune diseases, and a family history of autoimmune diseases. It is also frequently associated with angioedema. It responds poorly to omalizumab and antihistamines, but has a good response to cyclosporine. Patients with type IIb are also known to relapse more frequently after treatment-induced remission.

A Little Bit of Both

There are patients with chronic urticaria who do not fully fit either of these types. Current research does not know what proportion of people with chronic urticaria have a combination of the two.

What Does This Means for the Future ?

Except for the ASST used in the diagnosis of type IIb, there is currently no standardized test to confirm the type of urticaria a patient is suffering from. These tests will be important to personalize the type of therapy that can be offered according to the type or types of autoantibodies present in the patient and thus maximize the chances of response to treatment.

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