Allergic urticaria is a skin pathology of an allergic nature, which can be acute or (less often) chronic. Its symptoms are skin itching, the appearance of erythematous elements rising above the skin, similar to rashes remaining after a nettle burn – hence the name of the pathology. Diagnosis is made on the basis of examination of the patient, blood analysis, determination of the level of immunoglobulin E; it is possible to conduct immunological studies – allergic tests to identify the allergen. Treatment of allergic urticaria is performed using antihistamines, hypoallergenic diet, immunomodulatory drugs.
Allergic idiopathic urticaria is a skin disease manifested by the development of itching, erythematous rashes and usually provoked by food or other allergies. This condition is extremely common, according to medical statistics, at least 10-20% of the world’s population have experienced symptoms of this pathology at least once in their lives. In the vast majority of cases, allergic urticaria is acute and after treatment (sometimes spontaneously) disappears, leaving no traces on the skin or mucous membranes. The chronic form of the disease, according to some dermatologists, should be placed in a separate nosological group, since it is caused by autoimmune and hereditary factors. In addition to the true allergic form, there is the concept of “pseudoallergic urticaria”, which is caused by various physical factors.
Disease can affect a person at any age, however, the prevalence of children is observed in the age distribution of patients. This is due to the immaturity of many immunological processes, which easily causes allergies to various factors. The chronic type of allergic urticaria develops more often in female adults – in this case, it is often not possible to identify the cause of the disease, therefore it is often also called idiopathic urticaria. By itself, this pathology does not pose a threat to human life, but it can be complicated by angioedema or anaphylactic shock. These conditions require emergency medical care to save the patient’s life.
The causes of skin manifestations differ in different forms of allergic urticaria. This is usually a reagin type of hypersensitivity (type 1 allergy) mediated by immunoglobulins of type E. Allergens in this type of allergic urticaria are food components, plant pollen, household dust, some medicines and other factors. In this case, skin manifestations are just one of the symptoms of a food or other allergy. In some cases, allergies of the 2nd type can also cause such skin disorders – this mainly happens with blood transfusions. Intravenous administration of certain drugs with the development of an immunocomplex intolerance reaction can also cause allergic urticaria.
It has been noted that some infectious diseases, endocrine disorders, disorders of the psycho-emotional sphere increase the likelihood of developing allergic urticaria. This is especially true in relation to idiopathic, or chronic forms of pathology. The pathogenesis of the development of skin disorders in this case has been poorly studied, both immune and non-immune mechanisms of activation of tissue basophils of the skin are assumed. Therefore, in the presence of allergic urticaria of unspecified etiology, a complete examination of the patient’s body is performed in order to identify hidden and chronic diseases and disorders.
The main cause of skin disorders in allergic urticaria is mass degranulation of tissue basophils (mast cells). The granules of these cells include histamine, heparin, leukotrienes and a number of other biologically active compounds that can significantly alter metabolic processes in tissues. Basically, they lead to the expansion of blood vessels, increase the permeability of their walls, cause the accumulation of tissue fluid, stimulate the pain receptors of the skin, which leads to the appearance of itching. In most cases, such reactions with allergic urticaria are local in nature and affect only a certain area of the skin or, less often, the entire surface of the body. However, sometimes such a massive release of active compounds can lead to general reactions such as anaphylactic shock and Quincke’s edema.
With pseudoallergic urticaria, the pathogenesis is largely similar – there is a massive activation of tissue basophils of the skin with the release of biologically active compounds. However, the causes and mechanisms of this process are somewhat different – it may be congenital or acquired instability of mast cell membranes, their abnormal reaction to various physical or humoral factors. In addition, in some cases of pseudoallergic urticaria, the patient has an increased sensitivity of skin tissues to histamine and other components of basophil granules. Therefore, even a slight release of these substances can lead to a clinical picture of urticaria.
As mentioned above, all forms of allergic urticaria are divided into two types – acute and chronic. The boundary between them is rather arbitrary – it is believed that in the acute form of rash and itching persist for no more than 6 weeks, whereas if they bother the patient longer, a diagnosis of chronic allergic urticaria is made.
In addition, it is important to differentiate true allergic urticaria from pseudoallergia, in which the activation of mast cells occurs without the participation of immune mechanisms. There are many varieties of this condition – for example, the following are mechanical types of pseudoallergia:
- Dermographic urticaria (urticarian dermographism) – provoked by simple physical pressure on the skin (seams of clothing, for example). Nonimmune mechanisms of mast cell activation most often play a role in the pathogenesis of dermographic urticaria.
- Cold urticaria – this type of temperature urticaria has become more common in recent years. It was found out that in patients with this pathology, the level of certain platelet factors increases during cooling and the stability of the mast cell membrane decreases. Against the background of increased sensitivity of skin tissues to histamine, this can lead to the development of erythematous rashes and itching, both with local exposure to cold, and with the use of cold dishes and drinks.
- Thermal urticaria is a rather rare variant of urticaria. Just as in the case of urticarian dermographism, non–immune mechanisms of mast cell activation play a major role in the development of this type of disease – their degranulation occurs with an increase in temperature.
- Solar urticaria (photo allergy) – the provoking factor in this case is sunlight. In patients with this type of urticaria, there is an increased sensitivity of the skin to histamine, so degranulation of even a small number of mast cells leads to noticeable disorders.
- Vibrational urticaria is a rather rare form, often has signs of an occupational disease (in construction workers, in production). In this case, degranulation of basophils occurs due to mechanical tissue shaking.
- Aquagenic urticaria – previously did not belong to the mechanical varieties of urticaria, but in recent years there have been indications that the provoking factor in this case is the physical impact of water jets. Activation of mast cells of the skin occurs by a non-immune mechanism and is rather weak, but with increased sensitivity of tissues to histamine, this leads to the development of erythema and itching.
In addition to mechanical factors, an imbalance of the cholinergic autonomic nervous system can provoke the development of urticaria. This causes the development of the so-called cholinergic urticaria. In addition to the erythematous rashes and itching typical for this pathology, in this case there are also violations of sweating, regulation of skin temperature. This type of urticaria is often provoked by emotional experiences of a person. In addition, pigmented urticaria, which has the character of an autoimmune pathology, is close to this skin disease. With it, an increased amount of basophils accumulates in the skin tissues, which can easily be activated by various factors.
Symptoms of allergic urticaria
Despite the huge variety of types of urticaria, and factors that can provoke it, the symptoms of the disease are quite monotonous and differ only in their severity. One of the first manifestations is the development of itching and redness of the skin. Such phenomena can have both a local and widespread character, be located symmetrically (with the cholinergic type of pseudoallergic urticaria) or, much more often, asymmetrically. Blisters of various sizes (0.2-5 cm) appear very quickly (from several minutes to several hours) at the site of redness, which can merge with each other. An important diagnostic sign of allergic urticaria is the painlessness of blisters.
In most cases, these skin manifestations resolve within a day, leaving no traces behind – provided there is no repeated exposure to the provoking factor. Sometimes, with severe forms of allergic urticaria, the increase in symptoms occurs so rapidly that rashes on the skin develop into angioedema. The preservation of skin manifestations and the development of new rashes indicates the continuation of the provoking factor, which, in this case, may have an endogenous nature (as in idiopathic urticaria).
In clinical dermatology, the definition of this disease is performed using a significant number of diagnostic techniques due to the large number of forms of pathology. The examination reveals painless erythematous rashes protruding above the surface of the skin, having different sizes and localization. Diagnosis of the acute form of allergic urticaria, especially if it accompanies any allergy, is made on the basis of the patient’s allergic history and determination of the level of immunoglobulin E in the blood. The number of eosinophils in the blood is not a strict diagnostic criterion for this condition, especially its acute or sporadic form, but with long-lasting rashes, a slight eosinophilia is observed. By means of allergological tests, it is possible to identify the source of allergy and adjust the patient’s diet to prevent further attacks of the disease.
In those cases, if the rash does not disappear during the day against the background of a hypoallergenic diet and the exclusion of provoking physical factors, it is necessary to examine the lymph nodes, prescribe a general and biochemical blood test, and conduct a urine examination. All this will make it possible to identify a pathology that may have become a trigger factor for the development of allergic urticaria or to recognize the pseudoallergic form of this condition in a timely manner. The same should be done if the patient has an elevated temperature – urticaria itself does not cause hyperthermia, but some infectious diseases can cause both symptoms.
Each of the types of pseudoallergic urticaria (dermographic, cold, solar, etc.) is diagnosed by dosed exposure to a provoking factor. To do this, use a dermographometer, an ice cube, ultraviolet radiation with different wavelengths and other tools. The evaluation of the results, depending on the type of urticaria, the severity of symptoms and other factors, is carried out in a few minutes or hours, the maximum period is 48 hours. The positive result of the test will be the development of erythematous rashes and skin itching in the area of the study.
Treatment of allergic urticaria
The main link in therapy is to reduce the effect of histamine on skin tissue – this can significantly reduce swelling and itching. To do this, it is necessary to block H1-histamine receptors, this is achieved by using antihistamines. Currently, preference is given to antihistamines of the second (loratadine, cetirizine) and third (levocetirizine) generation. These drugs are very effective in acute forms of allergic urticaria, as well as dermographic and solar pseudoallergias. However, in chronic forms of urticaria and types with delayed symptoms (some types of pressure rashes), the effectiveness of antihistamines is greatly reduced.
For the treatment of chronic forms of pathology, as well as for the prevention of exacerbations with the recurrent nature of allergic urticaria, basophil membrane stabilizers (ketotifen fumarate) and calcium antagonists (nifedipine) are used. They significantly increase the activation threshold of mast cells, thereby hindering the development of skin manifestations. If there is a suspicion that the development of the disease is due to a decrease in the activity of the immune system, then immunomodulatory drugs are additionally prescribed. When a systemic pathology is detected, which is accompanied by allergic urticaria, a scheme for its treatment is developed.
In addition to prescribing medications, a hypoallergenic diet plays a significant role in the treatment of this condition to reduce the load on the human immune system. In addition, after determining the provoking factor (food or physical nature in pseudoallergia), it is necessary to take measures to exclude it from the patient’s life or minimize its impact on the body. In cases where allergic urticaria has a rapid character and leads to angioedema or anaphylactic shock, urgent life-saving measures are needed (injections of adrenaline and steroids, hospitalization).
Prognosis and prevention
The prognosis of acute urticaria in most cases is favorable – rashes disappear within a day, leaving no traces on the skin. In the absence of repeated exposure to the provoking factor, the disease often never bothers a person again. However, in the case of chronic forms of allergic urticaria, the prognosis largely depends on its type, severity, compliance by the patient with all the requirements of a dermatologist or allergist and the correctness of the prescribed treatment. Such persons should always adhere to a hypoallergenic diet (exclude eggs, chocolate, seafood and a number of other products from the diet). It is extremely important to identify the cause of skin disorders in order to minimize its impact. If urticaria was provoked by another disease, then the prognosis largely depends on the success of its treatment.
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