In this condition itching red weals develop; they resemble the effects of stinging nettle (Urtica dioica) on the skin. The condition may be associated with allergic reactions, infection, or physical stimuli, but in most patients no cause can be found. Similar lesions may precede, or be associated with, vasculitis (urticarial vasculitis), pemphigoid, or dermatitis herpetiformis.
The histological changes may be very slight but usually there is oedema, vasodilatation, and a cellular infiltrate of lymphocytes, polymorphs, and histiocytes. Various vasoactive substances are thought to be involved, including histamine, kinins, leukotrienes, prostaglandins, and complement.
Angio-oedema is due to oedema of the subcutaneous tissues; it can occur rapidly and may involve the mucous membranes. Hereditary angio-oedema is a rare form with recurrent severe episodes of subcutaneous oedema, swelling of the mucous membranes, and systemic symptoms. Laryngeal oedema is the most serious complication.
The physical urticarias, which account for about 25% of cases, include dermatographism and the pressure, cold, heat, solar, cholinergic, and aquagenic urticarias.
Dermatogyaphism is an exaggerated release of histamine from stroking the skin firmly with a hard object, such as the end of a pencil. Pressure urticaria is caused by sustained pressure from clothing, hard seats, and footwear; it may last some hours. Cold urticaria varies in severity and is induced by cold, particuarly by cold winds or by the severe shock of bathing in cold water. It appears early in life—in infancy in the rare familial form. In a few cases abnormal serum proteins may be found. Heat urticaria is rare, but warm environments often make physical urticaria worse. Solar urticaria is a rare condition in which sunlight causes an acute urticarial eruption. Tolerance to sun exposure may develop in areas of the body normally exposed to sun. There is sensitivity to a wide spectrum of ultraviolet light. Cholinergic urticaria is characterised by the onset of itching urticarial papules after exertion, stress, or exposure to heat. The injection of cholinergic drugs induces similar lesions in some patients. Aquagenic urticaria occurs on contact with water, regardless of the temperature.
Non-physical urticaria may be acute in association with allergic reactions to insect bites, drugs, and other factors. Chronic recurrent urticaria is fairly common. Innumerable causes have been suggested but, to the frustration of patient and doctor alike, it is often impossible to identify any specific factor.
Some reported causes of non-physical urticaria
• Food additives—for example, tartrazine dyes, sodium benzoates
• Salicylates—both in medicines and foods
• Infection—bacterial, viral, and protozoal
• Systemic disorders—autoimmune and "collagen" diseases; reticuloses, carcinoma, and dysproteinaemias
• Contact urticaria—may occur from contact with meat, fish, vegetables, plants, and animals, among many other factors
• Papular urticaria—a term used for persistent itching papules at the site of insect bites; it is also sometimes applied to urticaria from other causes
• Inhalants—for example, house dust, animal danders
Treatment of urticaria
• Eliminate possible causative factors, such as aspirin, and by a diet free from food additives
• Antihistamines. Also, H2 blockers, for example, cimetidine
• Adrenaline can be used for acute attacks, particularly if there is angio-oedema of the respiratory tract
• Systemic corticosteroids should not be used for chronic urticaria but may be needed for acute urticarial vasculitis
Berlit P, Moore P. Vasculitis, rheumatic diseases and the nervous system.
Berlin: Springer-Verlag, 1992 Champion RH, Greaves MW, Black AK. The urticarias. Edinburgh:
Churchill Livingstone, 1985 Czametzki BM. Urticaria. Berlin: Springer-Verlag, 1986
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