The role of trauma in the spreading weals of hereditary angio-oedema.

Twenty patients with hereditary angio-oedema (HAO) were regularly observed. Trauma often initiates the swellings of HAO which, once formed, may continue to spread. In the prodromal rash too, a narrow band of weals spreads out from a central point, which often corresponds to a site of trauma e.g. a pin prick. The relationship of these observations to the role of trauma in the initiation and spread of weals in other forms of urticaria is discussed.