urticaria

Urticaria, also known as Hives, is a reaction to different irritants that results in red, patchy, and itchy areas arising in the skin. It can be acute (short term) or chronic (long term) dependent on what causes the rash and how long it lasts for. The reaction occurs as high levels of histamine (the product released in allergic reactions and hay fever) are released into the body.

Epidemiology

The prevalence of short-term urticaria is approximately 12-23.5% [1]
Patients between 20-40 have been found to be more frequently affected by urticaria [2]
The global prevalence of urticaria in 2017 was 86 million people
Females have a greater burden of disease (measures the impact of living with illness and dying prematurely) than men [3]

Source: DermNetNZ.org

Urticaria
Red/orange hives in different patterns of patches

Source: DermNetNZ.org

Urticaria
Close up of a patch of darker urticaria

Causes [4]

Certain foods (eg. peanuts, eggs, nuts, shellfish)
Medications (eg. penicillin)
Insect stings/bites
Condition exposure eg. pressure, heat, cold
Latex exposure
Blood transfusions
Viral and bacterial infections
Pet fur
Pollen
Certain plants (eg. poison oak, stinging nettle)

Pathophysiology [5]

Medical students
- The cutaneous mast cell plays a central role in urticaria.
- Preformed histamine, tryptase, and cytokines are released from mast cells during degranulation.
- Histamine receptors on post-capillary venules and C-fiber nerve endings cause itching sensation in the central nervous system.
- Lesional skin biopsies show an early influx of inflammatory cells, including neutrophils, eosinophils, basophils, and undifferentiated T-cells.
- Cross-linking of allergen-specific IgE bound to FcεRI on mast cells or basophils initiates degranulation in allergic urticaria.
- Autoantibodies against IgE or FcεRI on basophils and mast cells cause histamine release and underpin autoimmune urticaria.
- Physical stimuli causing inducible urticarias may involve IgE and mast cells.
- Angioedema without wheals may be mast cell-dependent or independent, with bradykinin-mediated angioedema considered a different disease.
- Clinicians should actively confirm or exclude hereditary angioedema and other mast cell-independent angioedema through appropriate assessment, including C4 complement and C1 esterase inhibitor assays on fresh blood samples.
Patients
- Cells involved in the allergic response (mast cells) on the skin plays a central role in urticaria.
- Proteins (histamine, tryptase, and cytokines) are released from mast cells during degranulation (the process of the body responding to a wound by releasing substances from mast cells to trigger a cell- focused response).
- The histamine receptors on veins and nerve endings cause itching sensation
- Skin samples show an early entry of cells involved in inflammation, including cells like neutrophils, eosinophils, basophils, and undifferentiated T-cells.
- The connection of certain proteins onto mast cells or basophils triggers the process of mast cell release of substances in allergic urticaria.
- Immune proteins work against basophils and mast cells which causes histamine release and contributes to the body’s reaction to the formation of urticaria.
- Physical triggers causing urticaria may involve the protein, IgE, and mast cells.

Urticaria

Widely distributed urticaria across the upper back and neck with red circular borders and pale centres

Risk factors
- Exposure to certain conditions (eg. pollen, heat, UV, pressure, cholinergic- emotional trigger) [4,6]

Presentations [7]
- Elevated patches
- Itchiness
- Red coloured plaques
- Reddish- brown macules (spots)
- Spots with yellow/white colouration on darker skin

Urticaria

Swelling on the skin tissue and areas of depression/dimpled skin within the lesions

Investigations [6]
- Clinical examination of the appearance as well as a history of urticaria
- Tests for the liver function for hepatitis and thyroid function for autoimmune urticaria
- Erythrocyte sedimentation rate to investigation an underlying condition
- Full blood count to invest the presence of infections
- Allergy testing using a skin prick or patch test or IgE tests for specific allergic triggers that cause urticaria
- Elimination of food or drugs as urticaria triggers
- Urine test for urinary tract infection or renal involvement
- Physical challenges to determine the origin of urticaria
- Cold-induced- ice placed on the arm
- Dermographism- lightly scratching the skin
- Aquagenic- placing a body part into the water
- Cholinergic- exercising the person to trigger heat from sweating
- Delayed- pressure- 15 pounds of weight can be placed on the person’s shoulders to determine wheals with a delay of 4-6 hours

Differential diagnosis [8]
- Short-term (acute) sudden urticaria
- Long-term (chronic) sudden urticaria
- Physical urticaria caused by factors such as heat, pressure and water
- Drug exacerbation causing urticaria
- Insect bites
- Viral rash
- Atopic dermatitis/ allergic contact dermatitis- inflammation of the skin caused by allergens
- Irritant contact dermatitis- inflammation of the skin caused by irritants Eg. chemicals

Management [9]

Medical students
- Identify and manage underlying causes/triggers of urticaria, providing avoidance strategies if possible.
- Consider discontinuing drugs associated with chronic urticaria (e.g., NSAIDs) for several weeks as a trial.
- If the cause cannot be identified from the history, consider appropriate investigations for recurrent or persistent urticaria.
- Use symptom diaries and validated tools like Urticaria Activity Score (UAS7) to assess the frequency and severity of urticarial episodes.
  - For mild urticaria with identifiable and avoidable causes, advise that it may resolve without treatment.
  - For symptomatic cases, offer non-sedating antihistamines (cetirizine, fexofenadine, or loratadine) for up to 6 weeks or longer as needed.
  - In severe cases, consider a short course of oral corticosteroids in addition to the antihistamine.
- Consider referral to a specialist or dermatologist for children under 16 years requiring oral corticosteroids.
- If an inadequate response to first-line antihistamines, consider increasing the dose, switching to an alternative antihistamine, adding a leukotriene receptor antagonist, or prescribing topical antipruritic treatment.
- Consider adding a sedative antihistamine at night if itch interferes with sleep.
- Assess the impact of urticaria on the person's quality of life using validated tools like the Chronic Urticaria Quality of Life Questionnaire (CU-Q2oL).
- Refer to a dermatologist or immunologist for painful and persistent urticaria (suspected vasculitic urticaria), uncontrolled symptoms, angioedema with no wheals unresponsive to first-line treatment, acute severe urticaria due to food or latex allergy, or difficult-to-manage forms of chronic inducible urticaria (e.g., solar or cold urticaria).
- Consider referral to a clinical psychologist for people whose symptoms significantly affect their quality of life, causing social or psychological problems.
Patients
- Identify and manage underlying causes/triggers of urticaria, providing avoidance strategies if possible.
- Consider discontinuing drugs associated with long term urticaria (e.g., NSAIDs) for several weeks as a trial.
- If the cause cannot be identified from the history, consider appropriate investigations for recurrent or persistent urticaria.
- Use symptom diaries and validated tools like Urticaria Activity Score (UAS7) to assess the frequency and severity of urticarial episodes.
  - For mild urticaria with identifiable and avoidable causes, advise that it may resolve without treatment.
  - For symptomatic cases, offer non-sedating antihistamines (cetirizine, fexofenadine, or loratadine) for up to 6 weeks or longer as needed.
  - In severe cases, consider a short course of oral corticosteroids in addition to the antihistamine.
- Consider referral to a specialist or dermatologist for children under 16 years requiring oral corticosteroids.
- If an inadequate response to first-line antihistamines, consider increasing the dose, switching to an alternative antihistamine, adding a drug that work against leukotriene receptor (antagonist), or prescribing topical (applied to skin) anti-itch treatment.
- Consider adding a sedative (to make you feel sleepy) antihistamine at night if itch interferes with sleep.
- Assess the impact of urticaria on the person's quality of life using tools like the Chronic Urticaria Quality of Life Questionnaire (CU-Q2oL).
- Refer to a dermatologist or immunologist for painful and persistent urticaria (suspected vasculitic urticaria), uncontrolled symptoms, angioedema with no wheals unresponsive to first-line treatment, short term severe urticaria due to food or latex allergy, or difficult-to-manage forms of long term inducible (to be triggered) urticaria (e.g., solar or cold urticaria).
- Consider referral to a clinical psychologist for people whose symptoms significantly affect their quality of life, causing social or psychological problems.

Urticaria

Ring-like, red/pink raised lesions seen on the back on pale skin

Complications [10]
- Angioedema- swelling of the tissues
- Mental health complications such as stress and anxiety caused by presentation
- Anaphylaxis- a severe allergic reaction

Myths
- There is a cure for urticaria
- Long term urticaria is an allergic reaction
- Urticaria is never severe
- Urticaria is contagious
- Avoidance of certain foods is necessary to manage urticaria
- Treatment for urticaria is lifelong [11,12]

Questions to ask the doctor
- What lifestyle choices will help me manage symptoms of urticaria?
- How long will treatment take to be effective?
- How can you determine what triggers my urticaria?
- What can I do to prevent complications from arising