Atopic Urticaria: Phenotypes
Malcolm W. Greaves, MD
St. John’s Institute of Dermatology
St. Thomas’ Hospital
London, United Kingdom
Physical urticarias are common, by definition “atopic”, frequently passively transferrable and are presumed to involve reaction of a physically evoked neoallergen with specific IgE. The diagnosis is established by physical challenge testing in the clinic, and laboratory investigations are rarely warranted. Most have a natural history of eventual spontaneous remission, and respond to H1 antihistamines. However in a minority of patients symptoms can be severe, unremitting, and disabling, with substantial impairment of quality of life.
Four important physical urticarias will be discussed with regard to clinical presentation, pathophysiology and treatment.
Symptomatic dermographism needs to be distinguished from simple dermographism. In the latter there is no axon reflex flare or itch. Using a dermographometer challenge pressure of 49g/mm2 about 4% of the population have symptomatic dermographism. In a modified PK reaction, dermographic reactivity can be passively transferred by IgE. Most patients respond to suppression of dermographism by low sedationH1 antihistamines though off-label dosages are often required. Spontaneous remission usually occurs in 2-3 years.
Apart from the well known acquired cold contact urticaria, there are several variant phenotypes of cold urticaria including cold reflex urticaria, cold urticaria with cryoglobulinaemia and the familial cold autoinflammatory syndromes (FCAS). Recent advances include refined technology for accurate measurement of cold sensitivity. Cold urticaria is passively transferrable by IgE and there is convincing evidence of the role of virus infections in causation of some cases. Besides H1 antihistamines, cold tolerance treatment and occasionally omalizumab have been used in selected cases.
Cholinergic urticaria is common, and is significantly associated with atopy. Classically, cholinergic urticaria has been deemed to be due to aberrations in autonomic cholinergic innervation of eccrine sweat glands and consequent dermal mast cell activation. That autologous sweat and serum skin reactions are recently reported in cholinergic urticaria, as well as in atopic eczema, provides additional evidence of a link between the two skin disorders. As with other physical urticarias no laboratory tests are indicated once the diagnosis is confirmed by challenge testing. H1 antihistamines, often in off-label dosages, are effective, although attenuated androgens or omalizumab are of utility in severely incapacitated individuals, especially those with angioedema.
Solar urticaria can be passively transferred, and two types have been defined: type 1 in which an abnormal photoallergen is formed in sunlight exposed skin which elicits specific IgE antibodies, and type 2 in which sunlight evokes a normal chromophore antigen which also leads to formation of specific IgE antibodies. Exposure to wavelengths outside the action spectrum in individual cases causes subsensitivity to clinical sunlight exposure and this has been used with benefit in phototolerance treatment. However, most cases respond well to a combination of H1 antihistamines and sun barrier creams. Monochromator phototesting is useful in precisely defining the action spectrum in individual cases, and enabling focused selection of optimal sun barrier cream protection.
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