urticaria word

Urticaria (hives, ‘nettle-rash’) د.وسام اللامي
Urticaria is a common reaction pattern in which pink, itchy or ‘burning’ swellings (wheals) can occur anywhere on the body. Individual wheals do not last longer than 24 h, but new ones may continue to appear for days, months or even years. Traditionally,
urticaria is divided into acute and chronic forms, based on the duration of the disease rather than of individual wheals. Urticaria that persists for more than 6 weeks is classified as chronic. Most patients with chronic urticaria, other than those with an obvious physical cause, have what is often known as ‘ordinary urticaria’.

Classification

# Physical urticarias

Cold urticaria : Patients develop wheals in areas exposed to cold (e.g.on the face when cycling or freezing in a cold wind).A useful test in the clinic is to reproduce the reaction by holding an ice cube, in a thin plastic bag to avoid wetting, against forearm skin
Solar urticaria : Wheals occur within minutes of sun exposure.
Heat urticaria : after contact with hot objects or solutions.
Cholinergic urticaria : Anxiety, heat, sexual excitement or strenuous exercise elicits this characteristic response. The vessels over-react to acetylcholine liberated from sympathetic nerves in the skin. Transient 2–5 mm follicular macules or papules resemble a blush or viral exanthem .
Aquagenic urticaria : like cholinergic urticaria and is precipitated by contact with water, irrespective of its temperature.
Dermographism : most common type of physical urticaria, the skin mast cells releasing extra histamine after rubbing or scratching. The linear wheals are therefore an exaggerated triple response of Lewis. They can readily be reproduced by rubbing the skin of the back lightly at different pressures, or by scratching the back with a fingernail or blunt object.
Delayed pressure urticarial : Sustained pressure causes oedema of the underlying skin and subcutaneous tissue 3–6 h later. kinins or prostaglandins,rather than histamine, probably mediate it. It occurs particularly on the feet after walking, on the hands after clapping and on the buttocks after sitting.

#Hypersensitivity urticaria

This common form of urticaria is caused by hypersensitivity,often an IgE-mediated (type I) allergic reaction. Allergens may be encountered in 10 different ways
#Autoimmune urticaria
Some patients with chronic urticaria have an autoimmune disease with IgG antibodies to IgE or to FcIgE receptors on mast cells. Here the autoantibody acts as antigen to trigger mast cell degranulation.
#Pharmacological urticaria
This occurs when drugs cause mast cells to release histamine in a non-allergic manner (e.g. aspirin,non-steroidal anti-inflammatory drugs [NSAIDs],angiotensin-converting enzyme [ACE] inhibitors
and morphine).
#Contact urticaria
This may be IgE mediated or caused by a pharmacological effect. The allergen is delivered to the mast cell from the skin surface rather than from the blood. Wheals occur most often around the mouth. Foods and food additives are the most common culprits but drugs, animal saliva, caterpillars, insect repellents and plants may cause the reaction.


Presentation
Most types of urticaria share the sudden appearance of pink itchy wheals, which can come up anywhere on the skin surface. Each lasts for less than a day, and most disappear within a few hours. Lesions may enlarge rapidly and some resolve centrally to take up an annular shape.

Angioedema is a variant of urticaria that primarily affects the subcutaneous tissues, so that the swelling is less demarcated and less red than an urticarial wheal. Angioedema most commonly occurs at junctions between skin and mucous membranes ( peri-orbital, peri-oral and genital). It may be associated with swelling of the tongue and laryngeal mucosa.

Course

The course of an urticarial reaction depends on its cause. If the urticaria is allergic, it will continue until the allergen is removed, tolerated or metabolized. Only half of patients with chronic urticaria and angioedema will be clear 5 years later. Those with urticarial lesions alone do better, half being clear after 6 months.

Differential diagnosis

Insect bites or stings and infestations commonly elicit urticarial responses, but these may have a central punctum and individual lesions may last longer than 24 h. Erythema multiforme can mimic an annular urticaria. A form of vasculitis (urticarial vasculitis;p. 114) may resemble urticaria, but individual lesions last for longer than 24 h, blanch incompletely and may leave bruising after healing. Some bullous diseases (e.g. dermatitis herpetiformis, bullous pemphigoid and pemphigoid gestationis) begin as urticarial papules or plaques, but later bullae make the diagnosis obvious. On the face,erysipelas can be distinguished from angioedema by its sharp margin, redder colour and accompanying pyrexia. Hereditary angioedema must be distinguished from the angioedema accompanying urticaria as their treatments are completely different.

Investigations

Almost invariably, more is learned from the history than from the laboratory. Careful attention should be paid to drugs. If no clues are found in the history, investigations can be confined to a complete blood count and erythrocyte sedimentation rate (ESR). An eosinophilia should lead to the exclusion of bullous and parasitic disease, and a raised ESR might suggest urticarial vasculitis or a systemic cause. Patients frequently suspect a food allergy, but this is rarely found in chronic urticaria. Prick tests are unhelpful, although many patients with chronic urticaria are sure that their problems could be solved by intensive ‘allergy tests’, and ask repeatedly for them.

Treatment

The ideal is to find a cause and then to eliminate it. In general, antihistamines are the mainstays of symptomatic treatment. Cetirizine 10 mg/day and loratadine 10 mg/day, both with half-lives of around 12 h, are useful. If necessary, these can be supplemented with shorter acting antihistamines (e.g.hydroxyzine 10–25 mg up to every 6 h, or acrivastine 8 mg three times daily). H2-blocking antihistamines (e.g. cimetidine) may add as light benefit if used in conjunction with an H1 histamine antagonist. Chlorphenamine or diphenhydramine are often used during pregnancy because of their long record of safety, but cetirizine and loratadine should be avoided. Sympathomimetic agents can help urticaria, although the effects of adrenaline (epinephrine) are short lived. Pseudoephedrine (30 or 60 mg every 4 h) can sometimes be useful adjuncts .A tapering course of systemic corticosteroids may be used, but only when the cause is known and there are no contraindications, and certainly not as a maintenance therapy for chronic urticaria or urticaria of unknown cause. Low doses of ciclosporin may be used for particularly severe cases.