1/3 Urticaria, pathomechanisms and clinical forms of urticaria

Question 1

Morphologic subtypes of urticaria

Answer 1

urticaria rubra -
red, erythematous vascular dilation causing erythema and urticaria

urticaria porcelanea -
white, pale extravassation compresses the vessels

u. hemorrhagica
deep red, with RBCs in the extravasate

u. gigantea
Covering whole body segments

u. anularis
Spreading rim of erythema surrounding the hives

u. circinata
- forming a polycyclic pattern.

Question 2

Angioedema vs urticaria

Answer 2

Urticaria only affects the piapillary dermis.

Angioedema involves the whole dermis and subcutical layers of skin.

Question 3

Pathogenesis of urticaria

Answer 3

Degranulation of mast cells in the dermis
Histamine release causing arteriolar dilation, venous constriction, and increased capillary permeability.

Histamine release can be induced by many different factors, generating the various immunologic urticarias and physical urticarias.

Question 4

Treatment of acute urticaria

Answer 4

2nd generation antihistamine
10mg loratadine or cetirizine

If pruritis is causing great distress, use a sedating antihistamine

avoid corticosteroids if the edema is caused by an infection,
but they should absolutely be given if there are signs of anaphylaxis or laryngeal edema.
50-200mg prednisolone oral or i.v.

i.m. epinephrine 0.3-0.5 milliliters,
(dose for anaphylactic shock is 0.5mg MAX i.m. (0.15-0.5mg))

Question 5

Anaphylaxis treatment

Answer 5

1st: i.m. epinephrine, repeated every 10 minutes.
2nd: inhaled beta-2 agonist - a SABA - SALButamol aka Albuterol, or Levosalbutamol

3rd line: H1 and H2 antihistamines
Remove the cause

Glucagon should be administered to anaphylactic patients on beta-blockers if they have a hypertensive response to the treatment, or in refractory cases of anaphylaxis.

Maintain patients airway
Crystalloid fluid support

Watch patients carefully for the next 24 hours, due to frequent biphasic course of anaphylaxis, can recurr after 8 hours even if the first phase was properly managed.

Question 6

Types of immunologic urticaria (5+2)

Answer 6

IgE mediated - mast cells activated by previously sensitized allergic stimuli

Complement mediated - complement system activated by immune complexes

Autoimmune - Autoantibodies against the IgE receptor on mast cells.

Immunologic contact uricaria - mast cells activated by previously sensitized contact allergens.

Hereditary angioedema - in rare cases is accompanied by urticaria. Defect of C1 esterase inhibitor.

Acquired angioedema - autoantibodies against C1 esterase inhibitor

Question 7

Types of physical urticarias (7)

Answer 7

(note that the physical urticarias are all chronic urticaria)

Dermographism, factitious urticaria - excoriation induced urticaria. White dermographism, variant with urticaria porcelanea caused by scratches.

Cold urticaria - ice cube test

Solar urticaria - sunlight induced, may cause wheezing or syncope also

Cholinergic urticaria - caused by exercise-induced sweating (cholinergic innervation of sweat glands).
This is the most common physical urticaria.

Aquagenic urticaria - very rare, caused by water

Pressure angioedema - sustained pressure causes erythematous swelling, ie. sitting on the butt, walking on the feet. Occurs after a delay of 1/2-12 hours

Vibratory angioedema - familial or sporadic, vibrations induce it.

Question 8

Pathogenesis of angioedmea

Answer 8

Results from C1 esterase inhibitor deficiency.
Presents lab values as low C4 levels with normal C1 and C3 levels.

Caused by increased bradykinin formation, from excessive kallikrein and Hageman factor enzyme activity.

Question 9

Types of chronic urticaria

Answer 9

Idiopathic chronic urticaria >50% of the chronic uts.

All of the physical urticarias

Autoimmune urticaria

Possible contact urticaria from a recurrent contact

Question 10

Treating chronic urticaria

Answer 10

FIRST.
Rule out any causes of inducible urticaria, allergen tests and physical stimuli tests.
Halt drugs that might be inducing it if possible - NSAIDs, penicillin.

Check blood counts and ESR/CRP for any underlying infections or malignancies.

Check blood for autoantibodies.
Perform autologous serum skin test
Biopsy the lesion.

Rx:
1st line: second generation antihistamines.
Loratadine, Fexofenadine, Cetirizine

2nd line: if symptoms last >2 weeks
Increase dose up to 4X

3rd line:
Add on 
cyclosporine A - 
Montelukast - leukotriene receptor blocker
or
Omalizumab - anti IgE antibody