Physical urticaria

Physical urticarias provide a reproducible model for the study of mediators of inflammation. They also provide a diagnostic and therapeutic challenge for the clinician. Patient diaries using a daily notebook or monthly calendar can be useful in assessing triggering factors and frequency of reactions, along with the effects of therapeutic agents and procedures. It is not uncommon to see more than one physical urticaria in the same patient. All physical tests that relate to the patient's symptoms should be performed. Repeat physical testing may also be useful. Except for hereditary forms, there is a tendency for patients to improve spontaneously, although often not for several years. Once the symptoms have been controlled through medication, smaller doses may be sufficient to maintain control. Therefore, an attempt should be made to reduce dosage and thus minimize side effects. Single nightly doses of antihistamines may control urticaria, while minimizing the inconvenience caused by drowsiness. However, the clinician must remember that because the beneficial effect of antihistamines is through competitive inhibition of histamine at the H1 or H2 peripheral receptor level, continuous blood levels of antihistamines must be maintained. The new insights into the pathophysiologic mechanisms of the physical urticarias that continue to be learned will help researchers and clinicians to develop more rational and effective approaches to treatment.