Cholinergic urticaria

This is one of the most frequent types of physical urticaria. It is characterized for the emergence of a generalized itchy rash of multiple hives of one to three millimeters of diameter, surrounded by an erythematous halo which is triggered just a few minutes after the skin has been exposed to sunlight or heat, or after a situation of stress or emotional tension or intense exercise has taken place.

Although the pathogenic mechanism is not known with certainty, this condition seem to obey to intrinsic disorders at a cellular level which allows the releasing of mediators such as histamine in the presence of acetylcholine which proceeds from cholinergic nerve fibers. In fact in patients affected by this condition the characteristic lesions of cholinergic urticaria can be reproduced locally after twenty minutes of receiving the intradermal injection of 0.1 milliliters of a solution of methacholine on physiological serum.

Clinical manifestations for cholinergic urticaria

It usually affects to people with ages comprised between twenty and fifty years of age. After five minutes of intense exercise, or situations of high temperature or stress, patients start to present hives that are usually small (from one to three diameters), they mainly emerge on trunk, neck and upper extremities. The rush usually disappears spontaneously after twenty to sixty minutes. Sometimes the erythematous component can prevail in just a few hives. In mild forms of the condition, the patient only experiences itching as a response to exercise or heat but without visible changes in the skin.

On the contrary on severe manifestations of this condition, lesions can be accompanied (although this case is not very frequent) of systemic symptoms, diarrhea (cholinergic symptoms), tearing and salivation. Sometimes the lesions can also emerge with the formation of an angioedema in the trunk or face. In some cases all these symptoms are accompanied by bronchospasms; however this can be due to an association of the cholinergic urticaria with asthma induced by exercise. Finally, the anaphylaxis induced by exercise can be a manifestation of cholinergic urticaria. The natural history of the condition is usually oriented to improvement, with an average of duration of about seven years (although there can be some cases where the condition has been extended for more than twenty years).

Diagnostic of cholinergic urticaria

The diagnosis of this condition can be confirmed by the reproduction of lesions in the patient trough the elevation of the body temperature of the patient in about 0.7 to one Celsius degree. This procedure can be done in the following way:

• Submitting the patient to an intense exercise (for instance: climbing and descending stairs or running during five to ten minutes until sweating is produced) being able to observe after the exercise period the emergence of the typical lesions.
• Submitting the patient to a bath on hot water at a temperature of forty to forty two Celsius degrees.
• Lesions can also be reproduced by the application of the intradermal injection of methacholine (positive in 33% of the cases.).