Urticaria is characterized by an erythematous wheal accompanied by a
subjective sensation of itching . The urticarial response has been
described as a defense mechanism against an unwanted intrusion, a
contact with an allergen with which continued exposure leads to the
release of IgE antibodies . All forms of urticaria seem to involve
the irritability and degranulation of cutaneous mast cells. Mast cells
are located in the loose connective tissue and are more concentrated in
the perivascular areas such as the lips, eyelids, and scalp .
Multiple stimuli, both immunologic and non-immunologic, are considered
unwanted intruders and lead to the release of preformed mediators and
the generation of newly formed mediators [5,6]. Many inflammatory
mediators have been identified in urticaria; the most common of these is
histamine, which is vasoactive and generally causes symptoms such as
pruritus, erythema, inflammation, angioedema, and potentially fatal
hypotension. While histamine is the primary mediator found in all
physical urticarias, the variable success rate with histamine blockers
strongly suggests the presence of other mediators [5,7]. The measurement
of these mediators in the ***, however, is difficult due to rapid
THE PHYSICAL URTICARIAS
There are numerous types of urticarias, and countless etiologies.
Physical urticarias constitute approximately 17% to 20% of all
urticarias [5,8]. There are a number of ways of classifying the
urticarias; for example, they can be classified on the basis of
immunologic or non-immunologic etiologies, or by whether they are
chronic or acute. Table 1 depicts an overview of the urticarias based on
etiology and presenting cause. The physical urticarias are different
from other urticarias in that the characteristic wheals can be
reproduced by a physical stimulus such as cold, heat, pressure,
vibration, sunlight, water, exercise, and increases in core body
temperature . In addition to being a distinct group of reactions, the
physical urticarias can also be classified as acute, persisting for less
than 4 to 6 weeks, or chronic, persisting for more than 6 weeks .
The physical urticarias include cholinergic urticaria, cold urticaria,
dermographism, delayed pressure urticaria, solar urticaria, aquagenic
urticaria, ***y urticaria, external localized heat urticaria, and
exercise-induced anaphylaxis. These reactions may coexist, and the
symptoms may not be present to the same extent in different individuals.
It may be helpful to think of the physical urticarias as being on a
continuum, with some individuals having mild occasional symptoms, and
others experiencing life-threatening crises. Because an individual may
have mixed symptoms suggestive of several different types of urticarias,
it can be confusing to ascertain specifically which urticaria exists.
The physical urticarias are distinguished by the following
characteristics : 1. All can usually be reproduced with the
2. Wheal formation is intermittent and occurs soon after the application
of the stimulus (except in the case of delayed pressure urticaria). 3.
The eruption usually lasts less than two hours.
4. The condition occurs most frequently in young ***s.
5. The wheals have a distinctive appearance and location.
6. There may be systemic features such as flushing, headaches,
dizziness, or hypotension.
Thirty-four percent of all the physical urticarias are cholinergic
urticarias . They occur with exercise, anxiety, sweating, and passive
warming (such as with a hot bath or shower). The precipitating factor in
this reaction is elevated core body temperature. The rash of cholinergic
urticaria is smaller than classic urticaria (2 to 4 millimeter wheals),
surrounded by large areas of macular erythema. Intense pruritus almost
always occurs, and may occur without the presence of obvious wheals. The
reaction usually occurs within 2 to 30 minutes of the onset of exercise
or passive warming. Usually the rash begins on the upper thorax and
neck, and may spread to the entire body; however, the rash may be
isolated to specific areas of the body such as the legs. Itching,
erythema, and wheals usually subside within 30 minutes of the
termination of the stimulating activity. The affected individual may
also experience other symptoms of cholinergic stimulation such as
lacrimation, salivation, bronchospasm, and diarrhea. Cholinergic
urticaria is not usually associated with angioedema, vascular collapse,
or hypotension. Rare variants of cholinergic urticaria include
persistent erythema, exercise-induced anaphylaxis (see discussion on
exercise-induced anaphylaxis), cold-induced cholinergic urticaria,
and food-dependent, exercise-induced urticaria.