Urticaria, or hives, is a common problem seen in doctors’ offices. In some patients, in addition to hives, there may also be swelling of the lips or throat. This is called angioedema. The cause of the hives and angioedema is most likely degranulation of mast cells. Everyone has mast cells on the exposed parts of the body. Theses mast cells are loaded with histamine, leukotrienes, and several other chemicals. If these chemicals stay inside the mast cells, they do not cause any problems. Once they are released, the open up the blood vessels and create inflammation.
An inflammatory reaction in the outer layers of the skin is a hive. An inflammatory reaction in the deeper layers of the skin or in the GI Tract is angioedema. The question everybody asks is what makes these mast cells degranulate. The most common cause is an allergic reaction. However, these hives are acute and usually last no more than a few days. We can do skin testing and identify the allergen in these situations.
However, in chronic urticaria, infective agents like viral antigens may be the cause for the degranulation of the mast cells. These hives can last for weeks and sometimes for months.
Some physical factors like exposure to the cold and physical pressure can also degranulate mast cells. More common in this group is dermographism, but most of these hives have a “streaky” appearance.
Some medications such as morphine and codeine, and histamine-containing foods such as chocolate and eggplant, can also degranulate the mast cells. In some instances, we cannot find the causative agent (idiopathic urticaria). In occasional instances, malignant cells acting as a foreign antigen can also degranulate mast cells, but this is very unusual. Viruses and connective tissue disorders, even sinusitis can cause chronic urticaria & angioedema. The majority of cases, however, have no underlying disease and will resolve in time.
In acute reactions, giving epinephrine, a short course of oral steroids, and antihistamines are indicated. In chronic hives, the usual treatment is a long-acting antihistamine along with short-acting antihistamines and also using an H2 blocker like Tagamet on a regular basis for a few weeks and possibly a short course of oral steroids.
In spite of these treatments, some patients have chronic hives for months or years. In these instances, we do blood work and a chest x-ray to rule out any other illnesses that may cause these hives.