Urticaria is a commonly encountered skin condition with a multitude of causes. There are primary and secondary forms of urticaria. Most secondary causes are acute in nature and can be explained by an underlying disease state, medication, or food. Urticaria can be a manifestation of many disease states, such as Muckle-Wells syndrome. Urticaria can also be a secondary sequela of an underlying malignancy, acute or chronic infection, genetic disease, and rheumatologic disease. It can also be seen as an acute reaction in a patient with anaphylaxis.
Primary urticaria can be divided into subsets of disease. The most common type is chronic idiopathic urticaria. Other forms of primary urticaria include the physical urticarias. There are many forms of physical urticaria, and the astute clinician can perform provocative testing to determine the type. There is no known cure for urticaria, but most cases of primary urticaria spontaneously resolve within 2 to 3 years.
Clinical Findings: Primary idiopathic urticaria is one of the most frequently encountered forms of urticaria. If no underlying cause is found and the urticaria lasts longer than 6 weeks, it is given the designation chronic idiopathic urticaria. This form of urticaria comes and goes at will with no provocative or remitting factors. Lesions appear as evanescent, pink to red, edematous plaques or hives. They can occur anywhere on the body and can cause much distress to the patient because of their appearance and because of the severe pruritus. Patients are particularly distressed when the hives affect the face and eyelids, causing periorbital and periocular swelling. Patients with chronic urticaria usually undergo a battery of laboratory and allergy tests. A complete blood count, metabolic panel, chest radiograph, and measurements of thyroid-stimulating hormone and antithyroid should be performed, as well as testing for various infectious diseases if the medical history war- rants. Testing for hepatitis B, hepatitis C, and HIV infection can be done in the appropriate clinical setting. Patients with a travel history often undergo stool examinations for ova and parasites. A full physical examination is warranted, together with age-appropriate cancer screening. Most patients with chronic urticaria have no appreciable cause for their hives and are diagnosed as having chronic idiopathic urticaria.
The physical urticarias are a group of conditions that cause hives; they represent a unique form of chronic idiopathic urticaria in that there is a precipitating factor. There are many types of physical urticaria, including aquagenic and cholinergic forms and cold-, pressure-, solar-, and vibratory-induced urticaria. These forms are diagnosed based on the results of provocative testing. The clinical history often leads to the diagnosis and the appropriate testing regimen. As an example, a patient may develop hives only under tight-fitting socks. This is typical for pressure-induced urticaria. If the patient develops hives on appropriate provocative testing, the diagnosis is made.
Pathogenesis: The pathogenesis of urticaria is poorly understood. Mast cells play a critical role. A stimulus causes mast cells to release histamine, which acts on the local vasculature to increase vascular permeability. The increased permeability causes localized swelling. Some forms of urticaria, such as those seen in anaphylaxis, are caused by a type I hypersensitivity reaction. Other forms of secondary urticaria may be caused by specific immunoglobulin E (IgE) antibodies that interact with mast cells.
Many medications have been shown to cause mast cell degranulation without an IgE-mediated pathway. The most common of these are the opiates and anesthetic agents. Chemical transmitters other than histamine also play a role in urticaria; they include the leukotrienes, serotonin, and various kinins.
Histology: The histological findings in urticaria are bland. The specimen typically shows a superficial perivascular lymphocytic infiltrate with some dermal edema. The epidermis is normal.
Treatment: Treatment of chronic idiopathic urticaria is based on symptom relief. Antihistamines are the first-line therapy and can be used in combination. The lack of response can be frustrating for both patient and physician. Physical urticarias are treated in the same manner, with emphasis on avoidance. Patients who can avoid exposure to the physical stimulus responsible for the urticaria have been shown to have a better clinical outcome.