Urticaria, hives or wheals are raised, pink or red skin lesion that are usually associated with allergy. The lesion can be generalized or localized at certain body parts. It is a fairly common problem that everyone will experience in their lifetime. Some are mild, but some can be serious.
When the mast cells are stimulated by allergens, they release certain chemical mediators such as histamine etc. These mediators result in the dilation of the small blood vessels in which fluid will leak out from the vessels into the tissues under the skin, causing the swelling in urticaria and the itchiness.
Urticaria rash
Urticaria can be classified into a few types depends on its clinical manifestation
- acute (last<6 weeks)
- chronic (last>6 weeks)
- episodic (acute & intermittent)
Common causes of acute urticaria are allergy to certain foods or medication, insects bite and viral infection esp in children. The urticaria emerges within few minutes to few hours after the contact with allergens and typically goes away within a day.
If the urticaria does not really goes away and persist for more than 6 weeks, then it is called chronic urticaria. The causes for chronic urticaria are more complex and may overlap with causes of acute urticaria.
Causes of chronic urticaria include:
- Physical
- dermatographism
- pressure
- cold
- heat, exercise, stress (cholinergic)
- sunlight
- water (aquagenic)
- vibration
- Food consumption (milk, nuts, eggs, seafood etc)
- Insects bite/sting (scabies, bedbugs, fleas etc)
- Contact urticaria (latex, animals, foods etc)
- Medication and drugs
- aspirin
- NSAIDs
- ACE-inhibitors
- opioids
- alcohol
- Autoimmune conditions
- urticarial vasculitis
- systemic lupus erythematosus (SLE)
- autoimmune thyroid disorders
- rheumatoid arthritis
- Infection
- hepatitis B
- mycoplasma
- streptococcus
- herpes simplex virus
- helicobacter pylori
- mycobacterium tuberculosis
- Chronic idiopathic urticaria (no cause can be found)
The actual cause for chronic urticaria is not easy to determine accurately. History from the patients is important and it can suggest physical, medication and food related urticaria. For example if the urticaria rash appears after a hot bath, then it is likely a cholinergic urticaria. Physical challenge can be done if physical cause is suspected.
Papular urticaria
Laboratory tests are mainly done to rule out the presence of autoimmune disorders in chronic urticaria. Acute episode usually does not need any test. Tests that can be done include complete blood and differential count, ESR, CRP, IgE, ANA, RF, complement, thyroid function and its autoantibodies. Skin biopsy is beneficial only if urticarial vasculitis is suspected.
The type of tests to be done depends on clinical evaluation by the doctor. If no cause can be found after thorough examination and investigation, the urticaria is referred to as chronic idiopathic urticaria.
Most common and useful treatment for urticaria is oral non-sedating anti-histamine (2nd or 3rd generation). If anti-histamines do not work well, other types of medication can be tried. If you know what is the most likely precipitating cause, then try your best to avoid it. Sometimes chronic urticaria may improve after a few years.
No comments:
Post a Comment