Urticaria Flashcards
(34 cards)
. Explain the pathophysiology of urticaria and how mast cell degranulation contributes to its symptoms.
Urticaria results from mast cell degranulation, releasing histamine and other mediators. Histamine increases capillary permeability, causing fluid leakage into surrounding tissues, leading to wheals. This also stimulates sensory nerves, causing itching and erythema.
Describe the role of histamine in the formation of wheals and angioedema.
• Histamine increases vascular permeability and dilates capillaries, leading to localized swelling (wheals). In angioedema, histamine affects deeper tissues, causing more pronounced swelling.
- What are the main types of inducible urticaria? Provide examples for each.
• Symptomatic dermographism:
Triggered by skin stroking or tight clothing.
• Cold urticaria: Triggered by cold air or water.
• Cholinergic urticaria: Triggered by exercise, stress, or hot showers.
• Solar urticaria: Triggered by sun exposure.
• Delayed pressure urticaria: Triggered by sustained pressure on the skin.
- Compare and contrast dermographism and cholinergic urticaria in terms of triggers and presentation.
• Dermographism is triggered by stroking or scratching the skin, presenting as linear wheals. Cholinergic urticaria is induced by heat or stress, presenting as small, itchy wheals, often accompanied by cutaneous inflammation.
- Define wheals and describe their appearance and duration in urticaria.
Wheals are raised, itchy, red or pale lesions caused by fluid leakage. They typically last less than 24 hours, resolving without scarring.
Wheals are raised, itchy, red or pale lesions caused by fluid leakage. They typically last less than 24 hours, resolving without scarring.
Angioedema involves deeper tissue layers, lasts up to 72 hours, and may be less itchy but more painful. It often affects areas like the lips, eyes, and genitalia.
- Discuss the clinical features of chronic spontaneous urticaria and how it differs from acute urticaria.
• Chronic
• Chronic spontaneous urticaria presents as recurrent wheals for over 6 weeks without a known cause. Acute urticaria resolves within 6 weeks and is often triggered by infections or allergens.
- How does the distribution and appearance of wheals differ in acute anaphylactic reactions versus chronic urticaria?
• In anaphylaxis, wheals rapidly cover large skin areas, often with systemic symptoms like difficulty breathing. Chronic urticaria presents fewer, localized wheals without systemic involvement.
- Explain how chronic urticaria is aggravated by heat, viral infections, and certain medications.
• Heat and viral infections stimulate mast cells, worsening symptoms. Certain drugs like NSAIDs can trigger pseudoallergic reactions, exacerbating chronic urticaria.
- List the common infectious, allergic, and physical triggers for acute urticaria.
• Infectious triggers:
Viral (e.g., hepatitis), bacterial (e.g., dental abscess).
• Allergic triggers: Foods (e.g., peanuts), drugs (e.g., penicillin).
• Physical triggers: Pressure, cold, or heat.
- How does food pseudoallergy differ from IgE-mediated food allergy in urticaria?
• Food pseudoallergy involves non-immune mechanisms (e.g., salicylates, food additives) causing symptoms, whereas IgE-mediated allergy is an immune response to specific food proteins.
- Outline the differential diagnosis for urticaria.
• Insect bites/stings:
Central punctum, lesions last longer than 24 hours.
• Urticarial vasculitis: Lesions last >24 hours, may bruise.
Describe the key aspects of history-taking in a patient with urticaria.
• Include onset, duration, and triggers. Review systems for underlying diseases, medications (e.g., NSAIDs), and environmental exposures.
- What laboratory investigations are useful in chronic urticaria?
• CBC to detect eosinophilia (parasitic or allergic causes), ESR for inflammation, and specific tests if autoimmune or infectious causes are suspected
- When should investigations for urticaria be deferred?
• If the condition is acute and self-limiting, investigations can be deferred unless it persists beyond a few weeks.
- What is the primary treatment goal for urticaria?
• To identify and eliminate the underlying cause while relieving symptoms.
- What is the first-line treatment for urticaria, and how does it work?
• Antihistamines (e.g., cetirizine) block histamine receptors, reducing itching and swelling.
- List antihistamines that are safe during pregnancy.
Chlorphenamine and diphenhydramine are considered safe due to their long safety record.
- When are systemic corticosteroids used in urticaria?
• Only in severe cases, when the cause is known, and there are no contraindications.
- What is the role of omalizumab in chronic urticaria?
• Omalizumab is a monoclonal antibody targeting IgE, reducing mast cell activation in antihistamine-resistant cases.
- What adjunct therapies are available for urticaria?
• Sympathomimetics (e.g., pseudoephedrine), H2 antihistamines (e.g., cimetidine), and off-label drugs like methotrexate or ciclosporin.
- Why are beta blockers contraindicated in urticaria with anaphylaxis?
• They block adrenaline receptors, potentially worsening anaphylaxis
- What distinguishes hereditary angioedema from angioedema in urticaria?
• Hereditary angioedema lacks wheals, is non-itchy, and results from C1 esterase inhibitor deficiency, requiring different treatment.
- How does erysipelas differ from angioedema?
• Erysipelas has sharp borders, intense redness, and is often accompanied by fever, unlike angioedema.
