Physical and Cholinergic Urticaria

Physical urticaria is classified according to the nature of the eliciting stimulus, i.e., mechanical, thermal or electromagnetic (Table i). Rarely, urticaria has also been reported in association with decompression and with X-ray and argon laser treatment (reviewed in Henz et al. 1997). Cholinergic urticaria is often classified as physical urticaria since an increase in body heat is involved. Aquagenic urticaria is elicited by a chemical rather than a physical stimulus to the skin surface, with the water dissolving a water-soluble 

Physical urticarias are not known to be induced by specific occupations, but they may become manifest in this setting. This holds particularly for professions requiring heavy mechanical work. Increased physical and sportive activities may also explain the higher frequency of manifest cholinergic and delayed pressure urticaria in men (Table 1). Severely affected persons 

Eliciting stimulus Type of urticaria Time of onset Duration (h) Diagnostic test 

Sheering forces Dermographic urticaria 2-5 min 1-3 Firm stroking with a dermographometer 

Sheering forces Delayed urticarial dermographism 0.5-8 h 1-8 Same as above 

---

In some individuals, urticarial weals are provoked by physical stimuli, e.g. friction (dermographism), heat or cold. Exercise may induce weals, particularly on the upper trunk (cholinergic urticaria). Physical urticarias may require combined Hj- and receptor receptor antagonists fully to block the vascular effects of histamine, which causes flushing and hypotension. Cyproheptadine is usually the preferred choice of Hj-antihistamine but causes drowsiness. 

After local elicitation of cold urticaria, wheals and swellings can also spread over the entire skin, whereas in patients who react only to cold air when sitting in cold rooms, or to cold wind, lesions are generalized. Similarly, in cholinergic cold urticaria, wheals and swellings extend over the entire body. Cholinergic cold urticaria develops after physical strain in the cold and is characterized by small, transient wheals. 

---