Urticaria (acute, chronic) Flashcards
Define urticaria.
Urticaria (also called hives) are erythematous, blanching, oedematous, non-painful, pruritic lesions that typically last less than 24 hours and leave no residual markings upon resolution.
What % of urticaria is associated with angio-oedema?
Approximately 40% of episodes of urticaria have associated angio-oedema. Angio-oedema is swelling involving the deeper layers of the sub-dermis and can occur in both the acute and chronic setting.
How common is urticaria?
- Urticaria affects 10% to 25% of the population
- 30% will go on to have prolonged symptoms
- Acute urticaria is more common in children and adolescents
- Chronic urticaria typically affects adults (and women are more affected 1.5:1)
- ACE-i related angio-oedema is more common in black ethnic groups
What is the difference between acute and chronic urticaria?
Acute - Episodes that occur over a period of <6 weeks are generally considered acute, can be caused by a specific stimulus (usually hypersensitivity reaction), and are self-limiting.
Chronic - Episodes of hives that occur daily or almost daily over a period of >6 weeks are classified as chronic and appear to be “spontaneous”. They have a complex aetiology.
What is a common cause of acute urticaria in children?
Hypersensitivity reaction or underlying viral infections are a common cause of acute urticaria, particularly in children.
Summarise briefly the differences in investigations/management of acute and chronic urticaria.
Acute:
- Self resolving
- Diagnosis based on history and physical examination
- Antihistamines are mainstay therapy
Chronic:
- Diagnosis may require laboratory testing, depending on history
- Referral to a specialist may be needed
- Antihistamines are mainstay therapy
*For those who don’t respond to mainstay therapy options include omalizumab and immunomodulatory medications.
Angio-oedema in which locations is dangerous?
Angio-oedema involving the face or neck can potentially compromise the airway and requires prompt airway management
What is the pathophysiology of urticaria?
MAST cells are found everywhere including in dermis, sub-dermis, mucosal surfaces
- Soluble antigen (IgE mediated) –> mast cell activation –> degranulation –> release of vasoactive mediators including histamine, leukotriene C4, prostaglandin D2
- Vasoactive mediators –> 1) vasodilation, 2) increased vascular permeability –> oedema and pruritus
- Delayed release of cytokines (TNF, IL-4, IL-5) causes longer-lasting lesions
Biopsies of lesions contain CD4+ lymphocytes, eosinophils, basophils and neutrophils and sometimes immune complex depoosition
Urticaria is confined to the DERMAL layer; angio-oedema involves the SUB-DERMAL and MUCOSAL sites
What type of hypersensitivity reaction is urticaria? Which immunoglobulins are involved? What is the antigen?
- This is a type 1 hypersensitivity reaction
- IgE mediated
- Soluble antigen
What are the risk factors for urticaria?
- FH
- Exposure to trigger (drug/food)
- Recent viral infection - in children; non-IgE
- Insect bite
- Female sex
What are the most common causes of acute urticaria?
Allergy (IgE mediated reaction)
- Drugs - penicilins, sulfonamides, muscle relaxants, diuretics, NSAIDs
- Foods - milk, eggs, peanuts, tree nute, finfish, shell fish
- Insect bites
Other (non-IgE mediated mechanisms)
- Drugs - NSAIDs, opioids, vancomycin
- Radiocontrast dye
- Acute viral infection (in children)
What are the most common causes of chronic urticaria?
- 40% are thought to be autoimmune causes - IgG autoantibodies to high-affinity receptor for IgE or thyroid antibodies
- Idiopathic
- Strong emotional situations
Only 10% of those with chronic urticaria have an identifiable cause.
What are the clinical features of urticaria?
- Wheals
- Erythematous oedematous lesions
- Pruritus
- Resolution in 24hrs with no residual markings
- Swelling of face, tongue, lips
- Blanching lesions (non-blanching = vasculitis)
- Stridor - if severe laryngeal angio-oedema causing airway obstruction
What investigations would you do for urticaria?
- Usually diagnosed from history and physical examination
- Ask patient to keep a food diary if suspected trigger is food then re-introduce slowly.
Consider these for chronic urticaria:
- FBC with differential
- Complete metabolic panel
- Urinalysis - renal dysfunction in vasculitis -> proteinuria and WBC
- ESR and CRP - raised in vasculitic urticaria
- IgE receptor antibody and related tests - +ve in AI related chronic U
- TSH
- Antithyroid antibody - Hashimoto’s thyroiditis
- ANA - rheumatological conditions
- Skin biopsy - check for vasculitis
- C4 lecels - low in angio-oedema
- C1-esterase inhibitor level or function - low in hereditary AO
- C1q levels - low levels in acquired angio-oedema (normal in hereditary)
How do you manage urticaria?
- Trigger identification and avoidance
- H1 receptor antagonists (antihistamines) e.g. cetirizine 10mg OD or loratadine 10mg OD
- Systemic corticosteroids - if severe
- Adrenaline (0.3mg IM every 1-2hrs as required) - if severe or causing airway compromise
