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Urticaria
Urticaria may appear as blotchy, raised, itchy and painful skin rash sometimes called a “nettle rash” or hives. Up to 50% of patients will have an associated with tissue swelling (angioedema). Lesions tend to move about every 24 hours and “migrate” around on the body.
A patient with an urticarial lesions affecting
the arm and forearm.
Are there different types of urticaria?
Urticaria can be broadly divided into the following types:
Acute urticaria is often sudden, caused by a reaction to food or medication and can last between several hours and six weeks.
Chronic urticaria is diagnosed if the rash persists for six weeks or longer. The cause of this type is difficult to determine.
What are the causes of urticaria
Examples of common causes of acute urticaria
Foods |
Pets |
Medications |
Nuts |
Dog |
Penicillin |
Shellfish |
Cat |
ACE inhibitors |
Strawberries |
Horse |
Anesthetic medication |
Milk |
Aspirin |
|
Eggs |
In chronic urticaria, the cause is often undetermined. In these cases the urticaria is termed as Chronic Idiopathic Urticaria. Allergy is an unlikely cause of this form of urticaria. Recent reports demonstrated that patients previously designated as having chronic idiopathic urticaria can be divided into 2 groups: 40% to 50% with chronic autoimmune urticaria, and the remainder with chronic idiopathic urticaria. The characteristic feature of patients with chronic autoimmune urticaria is the presenceof “auto-antibodies” directed against IgE receptors on mast cells in the skin and tissues causing an enormous release of histamine. Up to 40% of patients in both groups may have concomitant tissue swelling (angioedema). The autoimmune subgroup has an association with thyroid disease and often has anti-thyroid antibodies in their blood.
Examples of triggers of chronic urticaria
Infection |
Medications |
Physical factors |
Systemic disease |
Parasitic |
ACE inhibitor |
Heat |
Thyroid disease |
Intense cold |
Lupus |
||
Sun exposure |
Inflammation of blood vessels (vasculitis) |
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Pressure / Vibration |
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Occasionally, swellings and non-itchy skin lesions may be caused by a deficiency of an important regulatory enzyme of the complement immune system known as C1 esterase inhibitor: This is disorder is called hereditary angioedema. This condition is a genetic disease characterised by recurrent episodes of potentially life-threatening tissue swellings (angioedema). Episodes of angioedema in these patients typically last 3 or more days, begin during childhood, and continue to occur throughout life. Your doctor will be able to distinguish between hereditary angioedema and other causes of urticaria and angioedema by performing specialised blood tests. The diagnosis is confirmed by the presence of a low serum complement 4 (C4) and absent or greatly reduced C1 esterase inhibitor level or function.
Do I need to have allergy testing ?
It is important to emphasise that allergy testing alone is of a limited value in determining the cause of urticaria. The patient’s medical history and physical examination should direct any diagnostic studies. Skin prick test and allergy specific blood tests are frequently used to determine allergic causes of urticaria. In selected patients, using the history and physical examination as guides, additional tests that may be considered include the following:
- Stool examination for parasitic infections
- Antinuclear antibody (ANA) titer
- Hepatitis B and C screen
- Thyroid function tests
- Antibodies directed against the IgE receptor in cases suspected of autoimmune urticaria
Do I need treatment for my urticaria?
Your doctor will determine which type of urticaria you have. In the majority of cases, treatment of the urticaria is straightforward. If there is an allergic cause, avoidance of the allergen is essential. Antihistamines, primarily those working on H1 receptors, are the first line of therapy. H2 antihistamines, such as cimetidine and ranitidine, may have a role when used in combination with H1 antihistamines in selected patients. Glucocorticoids stabilise mast cell membranes and inhibit further histamine release. They also reduce the inflammatory effect of histamine and other mediators. However, the use of glucocorticoids in acute urticaria remains controversial. It is generally acceptable to give a short course of corticosteroids to treat severe and refractory cases. Adrenaline (Epinephrine) is a life saving medication in anaphylaxis with severe urticaria and angioedema affecting the throat. It should be used with care and given to patients only when deemed appropriate. A self-injectable adrenaline preparation is also available for adults and children but it should not be prescribed unless there is a strong medical indication. In patients with autoimmune urticaria and urticarial vasculitis, the use of cyclosporine, azathioprine, methotrexate, colchicine, dapsone, indomethacin, hydroxychloroquine and intravenous immunoglobulin has had reported success.