++
For further information, see CMDT PART 6-32: REACTIVE ERYTHEMAS
+++
Essentials of Diagnosis
++
Evanescent wheals or hives
Intense itching; rarely, pruritus may be absent
Most episodes are acute and self-limited (1–2 weeks)
Urticaria is divided into acute and chronic forms
Chronic urticaria (episodes lasting longer than 6 weeks) may have an autoimmune basis
+++
General Considerations
++
Urticaria may be acute (less than 6 weeks' duration) or chronic (more than 6 weeks' duration)
Urticaria can result from many different stimuli on an immunologic or nonimmunologic basis
Most common immunologic mechanism is mediated by IgE, which is seen in the majority of patients with acute urticaria
Another involves activation of the complement cascade
Cholinergic urticaria is triggered by a rise in core body temperature (hot showers, exercise)
Cold urticaria is acquired or inherited and triggered by exposure to cold and wind
Chronic urticaria
Some patients with chronic urticaria demonstrate autoantibodies directed against mast cell IgE receptors
Autoimmune thyroid disease may be associated with autoimmune urticaria
Acute hepatitis infection may be associated with urticarial vasculitis
++
Lesions are itchy red swellings of a few millimeters to many centimeters
The morphology of the lesions may vary over a period of minutes to hours
Individual lesions in true urticaria last less than 24 h, and often only 2–4 h
Angioedema is involvement of deeper vessels, with swelling of the lips, eyelids, palms, soles, and genitalia
Angioedema is no more likely than urticaria to be associated with systemic complications such as laryngeal edema or hypotension
Dermatographism
In cholinergic urticaria, wheals are 2–3 mm in diameter with a large surrounding red flare
+++
Differential Diagnosis
++
++
Laboratory studies are not likely to be helpful in the evaluation of acute or chronic urticaria unless there are suggestive findings in the history and physical examination
A complete blood count with differential, erythrocyte sedimentation rate or C-reactive protein, thyroid-stimulating hormone, and liver chemistries might be appropriate for some patients with chronic urticaria
Functional ELISA test can detect patients with an autoimmune basis for their chronic urticaria
+++
Diagnostic Procedures
++
++...