Urticaria
Classification
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
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.
Histamine 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
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
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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