Urticaria, Angioedema, and Anaphylaxis Flashcards
Urticaria
The medical term for hives. pruritic, erythematous papules or plaques, with an erythematous border and often a lighter center.
Angioedema
The medical term for swelling
It is estimated that __% of the population experiences urticaria at some point in their life.
It is estimated that 20% of the population experiences urticaria at some point in their life.
Urticaria
Three sources of edema
- Lymphedema (indicative of inflammatory process or failure of lymphatic system)
- Edema arising from heart failure
- Edema arising from liver failure
Reflection coefficient
Denoted σ, ranges from 0 to 1. A measure of how open the capillaries are to fluid exchange, 1 being maximally open and 0 being impenetrable to fluid.
Pcap - Pint
The expression denoting the difference in hydrostatic pressure between the capillary space and the interstitial space
πcap - πint
The expression denoting the oncotic pressure difference between the capillary space and the interstitial space
Fick equation
J = σ { ( Pcap - Pint ) - ( πcap - πint ) }
Where J is the fluid flux rate between the capillary and the interstitial space
Anything that ___ will shift the balance towards the accumulation of fluid in the tissue and thus the development of (angio-)edema
Anything that increases the net hydrostatic pressure, decreases the net oncotic pressure, increases the reflection coefficient, or impairs lymphatic drainage will shift the balance towards the accumulation of fluid in the tissue and thus the development of (angio-)edema
As opposed to angioedema, “regular” edema is __
As opposed to angioedema, “regular” edema is gravity dependent
Angioedema classically affects the ___ and does not migrate based on ___.
Angioedema classically affects the lips, tongue, face, hands, feet, and genitals and does not migrate based on gravity.
Cutoff for acute vs chronic angioedema and urticaria
6 weeks
Differential diagnosis for angioedema with urticaria
- Urticarial vasculitis: occurs when IgG or IgM containing immune complexes, such as form in a serum sickness reaction or some autoimmune diseases, trigger mast cell activation. Often results in complement cascade and complement mediated inflammation as well.
- Hereditary and Acquired Angioedema: It occurs without hives or itching, and is the result of the action of a chemical called bradykinin on vascular endothelial cells. It does not involve histamine or other mast cell mediators much if at all.
- Angiotensin converting enzyme inhibitor (ACE-I) associated angioedema: Also a bradykinin mediated swelling. The ACE enzyme, which catabolizes bradykinin, is antagonized by the ACE-I antihypertensive drug and can lead to the accumulation of bradykinin and thus itchless and hiveless angioedema.
In dermal tissues, approximately __% of histamine receptors are of the H1 subtype
In dermal tissues, approximately 85% of histamine receptors are of the H1 subtype
Complement, Coagulation, and Contact Cascades in Angioedema
Chronic autoimmune urticaria
Represents an important subset of patients who have no clear external triggers for hives and swelling, and previously were told they had idiopathic urticaria/angioedema. Many patients with autoimmune urticaria and angioedema have an IgG autoantibody that binds to FcεRI, leading to cross-linking and mast cell activation and degranulation.
What triggers bradykinin mediated angioedema?
In disease such as hereditary angioedema (HAE), there is a congenital defect in one or both of the genes encoding the enzyme C1 esterase inhibitor (C1INH). Lack of C1INH activity allows for the abnormally high conversion of prekallikrein to kallikrein, which in turn generates excess bradykinin.
Angiotensin converting enzymes inhibitors (ACE-Is), a class of anti-hypertensive medications, block the activity of the ACE enzyme that helps degrade bradykinin.
Bradykinin activates the endothelium via
Bradykinin type-2 receptors
Treatment and Prevention
- Antihistamines
- Montelukast (cysteinyl leukotriene antagonist)
- Corticosteroids (at least for short term)
- Omalizumab (IgG anti-IgE)
Treatment and Prevention for Bradykinin-mediated angioedema
- Very different from the rest, so deserves its own category
- Will not respond to antihistamines or mast cell degranulation inhibitors
- Infusion of C1INH may arrest attack
- Bradykinin type-2 receptor blockers
- Kallikrein inhibitors
Etymologically, anaphylaxis is the opposite of. . .
. . . prophylaxis
” During attempts by Portier and Richet (1902) to immunize dogs, animals accidentally sensitized to previously sub-lethal doses of sea anemone venom died in a rapid, dramatic reaction the researchers termed ana (the opposite of pro = for)-phylactic (protection). “
You should strongly suspect anaphylaxis when you see a patient with:
- Acute onset of illness (min to hr) involving skin or mucosa and either respiratory compromise or shock
- Rapid onset of symptoms following exposure to likely allergen involving two or more of: GI symptoms, skin/mucosa, respiratory, blood pressure
- Clear evidence of shock following exposure to a known allergen
Frequency of anaphylaxis manifestation in various organ systems
