Urticaria is a common vascular reaction pattern characterized by dermal swelling due to vasodilatation and increased vascular permeability. Clinically, it is manifested as intensely itchy, erythematous or pale, oedematous swelling.
Mechanism
It is mainly due to local increase of permeability of the capillaries and the small venules. Histamine, which is derived from mast cell, is an important mediator. Kinins, prostaglandins, fibrinolysin system and complements are other important mediators.
Urticaria can be produced by wide variety of immunological and non-immunological (Physical, chemical, drugs) stimuli.
Provoking Causes
- Aero-allergens
- Blood products and bites (insects)
- Contactants
- Drugs
- Endogenons disease
- Foods
- Genetic diseases
- Physical urticaria
- Infections/Infestations and Idiopathic
Aero-allergens
Important aero-allergens are pollens, housedust, feathers, spores etc.
Blood Products and Insect Bites
Urticaria can be seen with blood transfusion. Bites or stings due to spiders, snakes, insects can produce urticaria by immunological as well as by non-immunological mechanism.
Contactants
Wide variety of contactants like drugs, dyes, cosmetics, tooth paste, fabrics, soaps etc. can be responsible for urticaria.
Drugs
Drugs can produce urticaria by immunological as well as by non-immunological mechanism. The common drugs are penicillamine, sulfonamides, codeine, aspirin and other anti-inflammatory agents, insulin, morphine, thyroid and parathyroid extracts.
Endogenous Diseases
This includes lupus erythematosus, malignancies, polycythemia, psycological factors and endocrinal disorders.
Food
Food allergy usually results in acute or recurrent attacks or urticaria, starting with in minutes or few hours of ingestion and lasting for few hours/days. Common foods are—nuts, fish, eggs, chocolate, tomato, milk, cheese etc. Preservatives and dyes in food are other important factors.
Genetic Diseases
It includes hereditary angioderma and familial cold urticaria.
Physical Urticaria
It is a distinct group in which localised oedema occur in response to physical stimuli i.e. cold, heat, solar rays, pressure, vibrations and water. Dermographism is a type of physical urticaria in which firm stroking of skin causes an exaggeration to triple response (erythema, oedema, and flare).
Infections/Infestations
Urticaria has been seen with viral, bacterial, fungal and parasitic infections. Mechanism is believed to be immunological.
Treatment
It is essential to take very careful and detailed history and make a thorough physical examination to detect the cause. If cause is found, avoidance of that causative agent is obviously the treatment of choice. However, due to difficulty in identifying or eliminating such a factor, symptomatic treatment should be given. Antihistamine drugs are the mainstay in the management of urticaria. The combination of H1 and H2 blocker (Cimetidine) may be effective in treatment of chronic urticaria. The tricyclic antidepressant (Doxipin) adrenergic agonist (Terbutaline) may be beneficial in a few cases. Systemic steroids are only indicated in very acute or recalcitrant cases.
Angio Oedema
This is a variant of urticaria in which subcutaneous tissue rather than dermis is mainly involved. It commonly affects the lips, periorbital tissues, genitalia and sometime even tongue and larynx. Itching is usually absent.
Treatment is same as that of chronic urticaria. Acute cases require adrenaline and corticosteroids.
