Urticaria is a common disorder. Chronic urticaria is defined as hives lasting longer than 6 weeks. What are the causes?
Causes of chronic urticaria fall into the following categories:
- physical
- allergic
- autoimmune
- idiopathic
What cells play a role?
Basophils and mast cells are the primary effector cells. They produce a variety of mediators including histamine, leukotrienes, prostaglandins, cytokines, and chemokines. This leads to vasodilation, fluid exudation, increased vascular permeability, and accumulation of additional secondary inflammatory cells.
What is the mechanism?
Two mechanisms have been investigated as possibly contributing to the pathogenesis of chronic urticaria:
- autoantibodies to FcεRI or IgE on mast cells and basophils - responsible for 30–50 % of cases
- dysregulation of intracellular signaling pathways involving Syk, SHIP-1, or SHIP-2 in basophils and mast cells
Anti-FceR1 autoantibodies in chronic autoimmune urticaria: IgG against FceRI (receptor for IgE) (click to enlarge the image).
What is the treatment?
The primary treatment for chronic urticaria is to treat the underlying pathology, if any can be identified.
In idiopathic cases the main pharmacologic treatment modalities include:
- H1 antihistamines
- H2 antihistamines
- antileukotrienes
- corticosteroids
In severe and recalcitrant cases of chronic and autoimmune urticaria, immunosuppressive drugs have been used, most commonly cyclosporin.
Recent studies suggested that omalizumab, an anti-IgE therapy, may be of benefit. Inhibitors of Syk are also being developed.
Chronic Urticaria Treatment (click to enlarge the image).
References:
Pathogenic Intracellular and Autoimmune Mechanisms in Urticaria and Angioedema. Katherine Altman and Christopher Chang, Clinical Reviews in Allergy and Immunology, Online First™, 7 June 2012.
Image source: Urticaria, Wikipedia, public domain.
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