| Chronic
idiopathic urticaria is defined as urticaria lasting longer
than 6 weeks, for which no obvious cause can be found. This
is the commonest type of urticaria in a dermatology clinic
and a study by Champion reported that 80% of urticaria is
chronic idiopathic urticaria.
Although symptomatic relief can be achieved
with drug therapy, a certain percentage of patients may suffer
from continuous symptoms for years without true remission.
Numerous factors have been suggested for causing
this disease including sea food, azo dyes, food preservatives,
candida in the gut and trace of penicillin in dairy products.
Some patients may benefit from elimination of one of these
factors, but for most others the cause of the disease remains
obscure. Recently an autoimmune aetiology has also been proposed.
By definition, no obvious aetiological factor
is apparent and special investigations are nearly always unhelpful.
For most patients with chronic idiopathic urticaria, a complete
blood count, ESR for screening may be adequate. Stool for
ova is indicated if there is eosinophilia. Other tests detailed
above should be performed for individual patient as directed
by the history and examination.
Prick test and intradermal skin test are often
positive but are difficult to interpret. Challenge tests with
food coloring agents and preservatives if available, are helpful
in the management.
Although no underlying cause can be found,
for the majority of patients their symptoms can be well controlled
by drug with minimal disturbance to their daily life. Depending
on the patient's tolerance, a sedating or non sedating antihistamine
can be prescribed during daytime. Because most patients have
more severe attack at night time, an additional nocte dose
of more sedating drug like promethazine is helpful.
The patient should be encouraged to keep a
food diary. Food containing tartrazine dye and preservatives
as well as drugs that known to aggravate urticaria should
be avoided. In suitable cases, elimination diet can be carried
out with the help of a dietitian.
Tolerance to antihistamine therapy may develop
in a patient whose symptoms are previously under control.
This tolerance cannot be overcome by increasing the dosage
or by changing to another antihistamine. The cause of tolerance
is thought to be due to the down regulation of the H1 receptors.
Ketotifen and sodium cromoglycate can be tried
and responsiveness to antihistamine may return. Hospital admission
may be required for alternative therapy in difficult cases.
What
is Urticaria ?|Classification
of Urticaria|Chronic
Idiopathic Urticaria|Cholinergic
Urticaria|
Cold
Urticaria| Urticaria
causes|Traditional
Chinese Medicine and Urticaria|Pressure
Urticaria|
Solar
urticaria
|
