Or “hives” – itchy plaques or papules (weals), with surrounding flare, typical of histamine reaction in skin. Urticaria can also be accompanied by angioedema – although angioedema on its own may point to hereditary angioedema (else drugs eg NSAID, ACE inhibitors, oestrogens, statins).
Not always allergy, although it is the classic rash of type 1 (histamine and IgE mediated) allergy. Can be inducible or inflammatory. Can be transient, intermittent or chronic. And often, no underlying cause can be found.
Inducible
Various kinds of physical stimuli can trigger urticaria, including:
- Dermatographism – within 10 minutes of pressure
- cf Delayed pressure type – tight clothing, sitting
- Heat (including exercise and emotion) – also called cholinergic urticaria
- Cold – can be secondary to autoimmune conditions or infection. Anaphylaxis risk from swimming!?
- Sunshine (solar)
- Water (aquagenic) – cold, hot, even rain…
Some tests have been suggested eg ice cube test (ice cube in a sealed plastic bag over the forearm for up to 10 min – wait for skin to rewarm), flannel test for aquagenic (wet towel for a few minutes on area of skin most affected).
Can be hormonal in girls, therefore cyclical (catamenial).
Differential
- Delayed food allergy eg alpha gal, or exercise induced
- Atopic dermatitis
- Chronic or recurrent infection (consider occult eg dental)
- Erythema marginatum (as in rheumatic fever, but also a prodrome to HAE!)
- Erythema multiforme
- Drug reactions
- Polymorphous light eruption
- Thyroid disorders
- Cutaneous mastocytosis
- Systemic lupus erythematosus
- Cryopyrin (autoinflammatory) disorders
- Urticarial vasculitis (often spectacular, bruising develops)
- Autoimmune urticaria (caused by autoantibodies vs FC epsilon RI alpha, but antibodies do not correlate well with symptoms)
- Mastocytosis
- Oestrogen, progesterone and pregnancy related dermatoses
And if everything else excluded, that leaves Chronic idiopathic urticaria. [EMJ. 2019;4[1]:39-47.]
Urticaria Activity Score available – wheals and itch over course of day, score 0-3. Moderate wheals are 20-50. Do for 7 sequential days and add up to give UAS7 score.
Diagnosis
Basophil histamine release assay and autologous serum skin tests suggested, 25% of all chronic urticaria patients are positive for one and/or other, but 50% are negative for both – so struggling for a diagnostic standard.
Consider:
- FBC, CRP, ESR
- ASOT
- Immunoglobulin electrophoresis done in adults to look for paraprotein
- H pylori – some have suggested eradication helps but BSACI come down against routine screening
- TFTs, Functional autoantibodies eg Thyroid, ANA
- Pseudoallergen (additives, flavourings, colourings) free diet for 3 weeks? BSACI not v keen
- Tryptase – systemic mastocytosis? Not in BSACI guideline!
- TTG – some case reports of association with coeliac disease
- C3/4 – if suspected urticarial vasculitis, and if reduced, measurement of anti-C1q antibodies [BSACI urticaria guideline]. C4 low in HAE.
- Cryoglobulins for cold induced
- Biopsy – but for mastocytosis, bone marrow aspirate most sensitive!
Specific tests: ice cube, flannel, dermatographism, hot bath, exercise.
Treatment
For acute, non-sedating antihistamines (H1 blockers), else steroids. Evidence for H2 blockers eg ranitidine very weak.
For chronic, non-sedating AH effective in <50% of patients. No evidence that one antihistamine is better than any other. Guidelines recommend up to 4x updosing (weak evidence – for levocetirizine and desloratadine, ironically). Good evidence for ciclosporin. Weak evidence too for steroids, zafirlukast, cimetidine, MTX etc. Omalizumab seems to work well – monthly SC injections for 6 months (from age 12). Side effects include headache, abdo pain, joint pain, fever. Rarely anaphylaxis so observe first few doses. Increased risk of parasitic infections in theory – avoid foreign holidays??
Tranexamic acid for angioedema.
No evidence for thyroxine treatment if autoantibodies, if euthyroid.
Note the high rate of anxiety, depression, somatising disorders (50%).
[BSACI 2015]