Urticaria, commonly known as hives, is the most frequent dermatologic disorder characterized by sudden onset of raised, well-circumscribed erythematous (red) and edematous (swollen) plaques or wheals affecting the dermis and epidermis. These lesions are intensely pruritic (itchy).
Classification
- Acute urticaria: Duration < 6 weeks
- Chronic urticaria: Duration > 6 weeks
Variants of Urticaria
- Acute IgE-mediated urticaria (allergic)
- Chemical-induced (non-IgE-mediated)
- Autoimmune urticaria
- Cholinergic urticaria (triggered by heat/sweating)
- Cold urticaria
- Mastocytosis / Urticaria pigmentosa (mast cell proliferation)
- Physical urticarias: pressure, vibration, solar, etc.
- Periodic fever syndromes: Muckle-Wells syndrome
- Others: adrenergic urticaria, contact urticaria, papular urticaria (insect bites), urticarial vasculitis
Epidemiology and Pathophysiology
- Affects 10–20% of the population at some point.
- Mast cells are central; histamine is the primary mediator causing vasodilation and increased vascular permeability.
- Mast cell activation may be triggered by:
- IgE-dependent mechanisms
- Direct non-IgE stimuli (drugs, complement fragments C3a, C5a)
- Autoantibodies against IgE or its receptor (FcεRI) in some chronic cases
- Acetylcholine sensitivity in cholinergic urticaria
Causes
Acute Urticaria
- Often due to exogenous allergens or acute infections.
- Food, drugs, insect stings, infections.
Chronic Urticaria
- Mostly idiopathic (75%)
- Autoimmune mechanisms in some cases
- Physical triggers (cold, pressure, heat)
- Infections (Helicobacter pylori, Lyme disease)
- Autoimmune diseases (SLE, thyroid disorders)
- Stress
- Rare syndromes (Muckle-Wells, mastocytosis)
- Nutritional deficiencies (iron, B12, folate)
Differential Diagnosis
- Atopic dermatitis (eczema)
- Maculopapular drug eruptions
- Contact dermatitis
- Insect bites
- Erythema multiforme
- Pityriasis rosea
- Urticarial vasculitis (painful, often systemic symptoms)
Diagnosis
- History and physical examination are crucial.
- Identification of triggering factors and lesion characteristics.
- Dermographism test (stroking skin causes wheal).
- Physical urticaria can be reproduced:
- Pressure test
- Ice cube test for cold urticaria
- Blood tests:
- CBC, ESR/CRP
- Thyroid function tests
- Autoantibodies if autoimmune suspected (ANA, ENA, dsDNA, RhF)
- Cryoglobulins in cold urticaria
- Skin biopsy if vasculitis suspected.
Treatment
First-line: Antihistamines
- Use non-sedating H1-antihistamines at standard or increased doses (up to 4x normal dose if needed).
- Examples: fexofenadine, cetirizine, levocetirizine.
- Acute attacks: short-acting antihistamines like acrivastine may be used.
- H2-blockers (ranitidine, cimetidine) can be added but evidence is limited.
Second-line and Adjunctive Therapies
- Doxepin: antidepressant with H1 and H2 blocking properties
- Ketotifen: mast cell stabilizer with antihistamine effects
- Mirtazapine: useful for sedative and antihistaminic properties
- Calcium-channel blockers: stabilize mast cells (nimodipine preferred)
- Leukotriene antagonists
- Colchicine: for delayed pressure urticaria
- Immunosuppressants:
- Methotrexate
- Cyclosporine or tacrolimus (reserved for severe cases)
- Mycophenolate mofetil
- Others: terbutaline (β2-agonist), phosphodiesterase inhibitors, pentoxifylline
Special considerations
- Steroids: for short-term use only due to side effects; may worsen upon withdrawal
- High-dose IVIg: used in resistant cases with variable success
- Cold urticaria: antihistamines often ineffective; NSAIDs may help in familial cases
Monitoring and Prognosis
- Chronic urticaria may spontaneously remit after 1–2 years.
- Regularly reassess need for treatment to avoid unnecessary long-term medication.
- Avoid known triggers where possible.
