Anaphylaxis, is a medical emergency characterized by the sudden onset of urticaria, angioedema, dyspnea, and hypotension. It is most commonly encountered :1fter the administration of penicillin or the ingestion of shellfish or nuts in persons who have specific IgE antibodies attached to their mast cells as a result of previous sensitization.
The physical urticmias include cholinergic urticaria and nrticarial reactions resulting from heat, ultraviolet light, cold, and pressure. In a simplistic way, dermographism, which is the appearance of urticaria at sites of firm stroking, can be considered as a variant of pressure urticaria.
Hereditary angioedema is a rare familiar disease in which affected persons lack the clesterase inhibitor for complement. In these individuals many nonspecific events trigger an unregulated initiation of the complement cascade with the consequent onset of sudden and severe angioedema. A few patches of reticulated erythema may also appear, but urticarial wheals are essentially absent. Long-term administration of androgenic hormones such as danazol is quite effective in preventing recurrent episodes.
Urticarial vasculitis is somewhat of a misnomer. The disease is characterized by the appearance of flat-topped erythematous papules, but these lesions remain in place for days at a time rather than possess the transient nature of true urticarial wheals. Biopsy reveals a neutrophilic vasculitis. These patients are often hypocomplementemic, and they may have symptoms and signs suggestive of a lupus-like syndrome.