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9th June 2025
Aetiology
The primary cells responsible for the pathogenesis of urticaria are basophils and mast cells, degranulation of which results in preformed vaso-mediators such as histamine to be released. The consequence of this is vasodilatation and increased permeability resulting in the manifestation of dermal oedema. IgE-mediated immediate hypersensitivity reaction is the typical mechanism by which mast cells are known to degranulate, however this is not present in all cases. IgE is probably less implicated in chronic urticaria. This is supported by a lack of correlation between IgE levels and disease severity. Patients with chronic urticaria show activation of the extrinsic pathway of the coagulation and fibrinolysis cascade, and this has been shown to correlate with disease activity. The implications are unclear but it suggests a more complex aetiology than simple mast cell degranulation explaining the disease process.
Urticaria is implicated in a host of larger disease processes. The most common of which are:
| Urticarial vasculitis | Urticarial lesions typically remain in the same location for greater than 24 hours +/- residual purpura;
more painful than pruritic angioedema in 40% of cases often accompanied by systemic symptoms such as fever and arthralgia, look for other organ involvement Lesions may be self-limiting in some cases. Antihistamines or NSAIDs may be used for symptom relief. In cases of urticarial vasculitis that are unresponsive to corticosteroids or immunosuppressive medications such as azathioprine, cyclophosphamide or ciclosporin may be trialed. |
| Cutaneous Mastocytosis | Reddish-brown maculopapular rash with positive Darier sign (urticarial reaction elicited by stroking lesion).
May have evidence of systemic involvement: peptic ulcers; lymphadenopathy; splenomegaly. May be diagnosed on clinical signs alone, however skin biopsy and histology is useful to confirm. Avoidance of triggers is an important part of management. Other measures for cutaneous lesions include anti-histamines, topical steroids, montelukast, and phototherapy. |
| Insect bites | Central punctum, obvious precipitant.
Managed with antihistamines. May require antibiotics if infection develops. |
| Sweet syndrome (acute febrile neutrophilic dermatosis) | An uncommon condition most often seen in middle-aged females. Usually occurs following an acute systemic infection or in the context of chronic disease (including rheumatoid arthritis, IBD, leukaemia, solid organ malignancies), but may occur sporadically.
Skin lesions are tender and painful, and may be papular, vesicular, nodular or resemble plaques. It is associated with fever, arthralgia, malaise, headache, and myalgia. First-line treatment is systemic corticosteroids, which may be required for a number of weeks. Colchicine, NSAIDs, dapsone and biologic agents may be needed in refractory disease. |
Table 1: Causes of urticaria (Adapted from (Antia et al., 2018)
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