Urticaria is generally classified as acute or chronic based on the length of time the symptoms persist. The clinical features and natural history are as varied and unpredictable as the etiology. An itchy wheal is the characteristic feature of urticaria and is defined as a localized transient edema of the upper part of the dermis. Histamine plays an important role in the allergic reaction. As a result of an antigen antibody reaction, various chemical mediators, such as histamine, bradykinin, SRS-A, and acetylcholine, are released and accelerate the vascular permeability. This phenomenon is caused by a Type I reaction. The accelerated vascular permeability leads to the onset of wheals. It is assumed that the accelerated vascular permeability is not always the result of an allergic reaction. Although urticaria is often classified as allergic or non-allergic, for better understanding, I prefer to classify urticaria by its onset mechanism.
Allergic urticaria: caused by an antigen antibody reaction.
Histamine urticaria: caused by the release of histamine; pathogenesis is unclear.
Cholinergic urticaria: caused by the secretion of acetylcholine at sympathetic nerve endings.
Quincke’s edema: a variant of urticaria involving the subcutaneous tissue.
Allergic urticaria is a local manifestation of a Type I reaction and may be a manifestation of cutaneous anaphylaxis. The lesions may occur at any location. They are intensely itchy, especially at the onset. Certain foods, drugs and insect bites are thought to be the causes of urticaria. When the gastro-intestine is not functioning well, a food allergy appears as acute or recurrent attacks of urticaria. Drug-induced urticaria is the result of an allergic reaction to an antibiotic injection. Acute urticaria sometimes occurs after a bee sting. In a few cases, acute allergic urticaria may develop into anaphylactic shock. Drip infusion of steroids is effective for the treatment of this anaphylactic shock. In some cases, in which the causes of urticaria are clearly identified, the acute attack may last only a few hours or days. But, in fact, there are many other cases that do not respond to treatment within a month, and as a result, the disease continues to the chronic phase. Salicylic acid, antiphlogistic analgesic agent, and food additives such as artificial food coloring can trigger chronic urticaria. Nowadays, numerous foods (spinach that contains histamine and acetylcholine, eggplants, buckwheat noodles and bamboo shoots) can aggravate urticaria. Catching a cold can also lead to chronic urticaria.
This urticaria is caused by the release of histamines, but the allergic mechanism is not always identifiable. Also called mechanical urticaria, this disease includes factitious urticaria, cold urticaria, heat urticaria, and solar urticaria. Heat urticaria is almost the same as cholinergic urticaria. Wheals, which occur on exposure to cold air or water, are characteristic of cold urticaria. It is dangerous for cold urticarial patients to swim in cold water. Drinking something cold (beer, juice, water) quickly may cause wheals to appear on the pharynx, resulting in dyspnea. Solar urticaria develops within a few minutes of exposure and normally fades within an hour or so. Both of these features serve to distinguish from polymorphic light eruption in which there is a delay, often of several hours, between exposure and the onset of the eruption and in which the rash usually persists for days or longer. Many patients develop solar urticaria only when exposing areas of skin normally shielded from sunlight by clothing, and normally exposed skin such as the face and dorsa of the hands may be unaffected. This observation is probablly explained by the development of tolerance in chronically exposed skin. Sudden exposure of large areas of skin to sunlight may lead to widespread urticaria and the development of symptoms such as headache,faintness and even loss of consciouness. Histamine has an important role in the onset of mechanical urticaria, but a specific antigen antibody reaction has not yet been identified.
Cholinergic urticaria is a very distinctive type of urticaria in which characteristic small wheals (less than 1 cm across) occur in association with perspiration. When perspiration, exercise and strain stimulate a sympathetic nerve ending, acetylcholine is released and small wheals suddenly appear. Cholinergic urticaria most often occurs in the evening and at night. The onset mechanism is still unknown. Whether histamine is released or not is also uncertain. The disease characteristically occurs in adolescents and young adults. The patient complains of itchy wheals, which appear after exertion. The condition lasts for some months or years. Acetylcholine has something to do with psychogenic urticaria, the cause of which is thought to be stress.
Quincke’s edema is called angioneurotic edema or angioedema. This is a variant of urticaria in which histamines and serotonin are released in the subcutaneous tissues, rather than in the dermis. The clinical features are localized swellings of the eyelid, lips and buccal region with feverish itching. The pharynx and larynx may also be affected, resulting in dyspnea. The cause of Quincke’s edema is uncertain. Preliminary symptoms such as anorexia, gastrointestinal troubles or headaches are possibly related to the onset of Quincke’s edema. The treatment is essentially as the same as chronic urticaria.
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