Urticaria

Although this cutoff is somewhat arbitrary, hives that last longer than 6 weeks are considered chronic.  It is estimated that 15% of all people will develop urticaria at some point in their lives.  Of those with chronic hives, some 80% are idiopathic, the medical term which means that no cause, allergic or otherwise, can be found.

What causes hives?

Hives come about when mast cells, which are part of the skin, release chemicals like histamine that cause blood vessels to “leak” and produce swelling, redness, itching, and the other manifestations of urticaria.

1.    Allergy.  As noted above, many people think of hives as allergy, and indeed allergies can cause urticaria and angioedema.  Some allergic causes include:

•    Medications, such as antibiotics
•    Stings from bees or wasps
•    Foods like fish, eggs, shellfish, and nuts

Anaphylaxis. Some allergic reactions, such as those caused by bee stings and injections of antibiotics, can be serious, producing anaphylactic shock.  Patients who develop this have not just hives but wheezing, shortness of breath, tightening of the chest, faintness, and collapse.  Anaphylactic shock is a medical emergency which requires urgent attention and treatment that includes injection of epinephrine (adrenaline) and administration of intravenous fluids.  People prone to such reactions need to have epinephrine with them at all times (an Epi-pen.)   It should be emphasized, however, that most patients with hives, even the dramatic-looking welts all over the body that young children often get during viral infections, do not cause anaphylaxis and do not progress to the point of shock.  

2.  Infection.  Hives may be associated with a variety of bacterial, viral, and fungal infections.  Whether these infections actually cause hives or are just coincidences is hard to prove in many cases.

3.  Medications that release histamine.  Morphine, codeine, aspirin, and other non-steroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen) can make the body release histamine and develop urticaria through non-allergic mechanisms.

4.  Physical urticaria.  Many patients develop hives when external physical influences cause mast cells to leak histamine.  Here, too, no allergy is involved.  Examples include:

•  Derrmographism.  This literally means “skin writing.”  To some extent everyone gets a welt when something sharp or firm (a fingernail, belt, or bra strap) rubs against the skin.  This becomes a medical issue when, often for no specific reason, the skin’s mast cells release more histamine than usual, producing bigger lines and welts, and a lot of itch.

•    Cholinergic urticaria.  These appear as hundreds of small, itchy bumps when the body is exposed to heat, such as in a shower or after intense exercise.  They are almost always gone in a few minutes, before a doctor can see them, but their description usually gives them away.

•   Cold urticaria.  This condition is much rarer, as well as more serious.  Patients who have it may develop severe hives when exposed to cold weather or when swimming in cold water.

•    Contact urticaria.  These can be caused by contact with plants (like nettles) or chemicals (like latex.)  As with other kinds of physical urticaria, the location of the hives helps make the diagnosis, since the hives appear where the skin has contacted it.  (This is in contrast with ordinary hives which, allergic or not, appear all over the place.)

•    Others: heat urticaria, solar urticaria (hives after sun exposure), vibratory urticaria, pressure urticaria, aquagenic urticaria.

What kind of medical evaluation do urticaria need?

Physicians evaluating hives need to know whether patients have eaten any new foods, taken any new medications, or had any unfamiliar environmental exposures.  To be relevant, these would need to be recent; drugs taken for weeks or longer are unlikely to be culprits.

Most patients with hives who consult dermatologists have already inventoried everything they eat, wash with, or use to launder their clothes, and have determined that, indeed, nothing is new.   In general, if an allergic cause isn’t obvious--a bee sting, a shot of penicillin--there is no allergy to be found.

Blood tests for autoimmune diseases and food allergies, as well as other forms of allergy testing, are often performed to evaluate urticaria but hardly ever show anything abnormal.  

Some doctors recommend keeping a diary to look for “triggers” of urticaria.  Such diaries, besides being very boring to read, are not often useful as tools of evaluation.

Because urticaria come and go so randomly, correlations are easy to find (with whatever patients ate yesterday) only to break down (when the same food doesn’t produce them next time.)   These sequential broken correlations cause some patients to conclude that they are “allergic” to a whole series of foods and detergents; they would be better off concluding instead that they are allergic to none of them.  With rare exceptions, although “hormones” are often invoked as a cause of hives, most women do not get hives at specific points in their menstrual cycle.  While it is frustrating to have annoying welts for which there is no discoverable reason, it is even more annoying to skip all sorts of tasty and useful things and not be any better off.

How are urticaria treated?

1.  The mainstay of treating hives is the use of antihistamines.  Those available over-the-counter are loratadine 10 milligrams (Claritin), which does not cause drowsiness, cetirazine 10 milligrams and (Zyrtec), which is mildly sedating.  Older OTC antihistamines are diphenhydramine 25 milligrams (Benadryl), and chlorpheniramine 4 milligrams (Chlor-trimeton), both often quite sedating.  Please note that these are “adult¨ doses.  Doses for children range with a child’s age and size, and should be checked with a pediatrician.  Also, some antihistamines come with a decongestant (like Claritin-D, Zyrtec-D).  This decongestant component is not necessary for treating urticaria.

Other antihistamines require a prescription.  Those that cause little sedation are:
•    Fexofenadine (Allegra)
•    Levocetirzine (Xyzal)

Sedating prescription antihistamines include:
•    Hydroxyzine (Atarax)
•    Cyproheptadine (Periactin)

In unresponsive cases physicians supplement treatment the listed with others, known as H2 blockers, like cimetidine (Tagamet) and ranitidine (Zantac).

2.  Oral or injectable steroids (prednisone, methylprednisolone) can help reduce swelling and discomfort in severe cases of urticaria.  Steroids can, however, cause serious side-effects when used for extended periods and are therefore of limited benefit in a condition like urticaria which can last for weeks or months.

3.  A variety of other treatments have been used for urticaria as well, including montelukast (Singulair), ultraviolet radiation, antifungal antibiotics, agents that suppress the immune system, and tricyclic anti-depressants (amitryptyline, nortryptiline, doxepin).  The length of this list testifies how common urticaria are and how frustrating they can be to treat.  Evidence to support the benefit of such treatments is sparse.  In ordinary cases they are rarely needed.

4.  Topical (external) treatment: Topical therapies for hives include creams and lotions which help numb nerve endings and reduce itch. Ingredients which can accomplish this are camphor, menthol, diphenhydramine (Benadryl), and pramoxine.  Many of these topical preparations require no prescription. Cortisone-containing creams (steroids), even strong ones needing a prescription, are not very helpful in controlling the itch of hives.

How can you tell when a treatment for urticaria is “working”?

Although this question is fundamental, answering it is quite difficult.  After all, hives appear suddenly, fluctuate erratically, and disappear mysteriously.  Treatments like antihistamines help by reducing the number and itchiness of hives.  Especially in chronic urticaria, they don’t eliminate the welts altogether.  (If the hives go away completely for several days, that usually means the episode is over and treatment is no longer needed.)

Keeping this in mind, patients suffering from urticaria should keep several things in mind:

•  If they are unaccompanied by wheezing and tightness in the chest, even dramatic hives are unlikely to be serious or life-threatening.
•    Unless the cause is clear-cut and obvious, there probably isn’t one.
•    Treatment helps symptoms but doesn’t eliminate the problem.  
•    Hives that come for no reason usually also go for no reason.
•    Aspirin rarely causes hives, but may aggravate them and is best avoided.
•    Even when patients have chronic urticaria, the hives often go away after long periods (months to years.)

References

For further information, I recommend:

•    New Zealand Dermnet (http://dermnetnz.org/reactions/urticaria.html)  In the best tradition of British-inspired clinically-oriented medicine, this site is clear, sensible, and well-written.  Good pictures, too.
•    The Mayo Clinic site has a good article on hives as well:  http://www.mayoclinic.com/health/hives-and-angioedema/DS00313.