Anaphylaxis
What is anaphylaxis?
Systemic anaphylaxis is characterized by the presence of two or more of urticaria / angioedema, bronchospasm, gastrointestinal symptoms and hypotension. It is the end result of catastrophic mast cell degranulation, triggered by IgE-dependent or independent mechanisms (Table 1). Some patients will manifest milder or intermittent symptoms (such as short-lived urticaria) only when co-factors such as exercise are present. Occasional patients suffer from idiopathic anaphylaxis, where extensive evaluation fails to identify an underlying cause. Specialist evaluation is recommended after a diagnosis of possible anaphylaxis.
Patient evaluation
An anxious patient will enthusiastically
relate a series of relevant and irrelevant events and theories
as to causation. It is useful to undertake a structured interview
to first determine whether anaphylaxis occurred before
examining the surrounding circumstances to define a cause. Disorders
mimicking anaphylaxis should be considered in the differential
diagnosis (Table 2).
Exposure to stinging insects, food, beverage and medication in
the previous 12 hours should be recorded. This is because anaphylaxis
generally occurs within minutes of a sting, and within hours of
a food or drug allergen.
The presence of known food allergy should be recorded and the
possibility of accidental exposure considered. A commonly missed
form of food allergy is known as Oral Allergy Syndrome
in which an itchy mouth or angioedema develops soon after eating
fresh fruit or semi-cooked vegetables. Affecting mainly hay fever
patients with pollen allergy, anaphylaxis may sometimes occur
if ingestion is followed by vigorous exercise.
Co-factors that enhance the likelihood or severity of an allergic
reaction (such as exercise, alcohol, spicy food, NSAIDS or a high
ambient temperature on the day of reaction) should also be identified.
Exercise and anaphylaxis
Exercise-induced anaphylaxis typically
affects young adults. Manifestations include itch, urticaria /
angioedema, bronchospasm, sweating, syncope, gastrointestinal
symptoms and nasal congestion. Some experience symptoms with exercise
alone; others will only do so if allergenic foods are ingested
around the same time.
Foods implicated in this syndrome include wheat and other cereals,
celery, seafood, nuts, fruit and some vegetables. Mast cell degranulation
appears to be triggered by cross-linking of allergen-specific
IgE combined with neuropeptide release by adjacent nerve endings.
The syndrome of food and exercise-induced anaphylaxis usually
occurs during exercise. The severity of symptoms is generally
influenced by the amount of food ingested, the vigor
of exercise and the time between the two. Thus severe
symptoms are usually due to food eaten only a few hours earlier.
Less commonly, symptoms are triggered when the allergenic food
is ingested following exercise.
Investigation
Skin prick testing of patients (based on the history of events
as well as a "screen" with other common allergens) will
often detect candidate dietary allergens for either provocation
testing or avoidance. Testing is normally performed using commercial
food extracts. Occasionally, it is necessary to repeat testing
with the actual food prepared as eaten. This is because some protein
allergens are denatured by commercial extraction procedures.
RAST testing is less reliable and remains invalidated for all
but a small number of foods. Total IgE or RAST testing of food
mixes frequently provides misleading or irrelevant results. The
scientific validity of "alternative tests" such as the
cytotoxic food test, the Vega test, bioelectrical testing, hair
analysis, pulse test or kinesiology has not been demonstrated
(reviewed at "Quackwatch": http://www.quackwatch.com).
Challenge testing with foods, medication or exercise (under strictly
supervised conditions) is sometimes required. Negative challenge
testing with food followed by supervised exercise does not, however,
always exclude the diagnosis.
Management
Patients at risk of anaphylaxis should
wear an identifying MedicAlert bracelet, which will increase the
likelihood that adrenalin will be administered in an emergency
(Tel 1800 882 222; Fax 1800 643 259; http://www.span.com.au/medic).
They should avoid medication that may enhance the severity of
anaphylaxis or complicate its treatment. Beta blockers (and perhaps
ACE inhibitors) fall into the first group as they inhibit counter
regulatory mechanisms that may protect from uncontrolled hypotension.
Patients in whom episodes are unpredictable, who are allergic
to foods that are extremely difficult to avoid or when the cause
cannot be identified should carry injectable adrenalin (epinephrine)
and be trained in its use. Patients in whom exercise is a co-factor
are best advised to premedicate with H1 and H2 antagonists, to
carry injectable adrenalin, to not exercise alone and to consider
carrying a mobile telephone.
Immunotherapy
Immunotherapy is effective for the
treatment of inhalant allergies and bee or wasp stings. Unfortunately,
there is no reagent at this time for down regulating "jumper
ant" or tick reactions. Attempts to modify the severity of
food allergy using similar techniques have failed.
Emergency Action Plan
Since episodes of anaphylaxis are unpredictable,
a well thought-out "Action Plan" is an essential part
of management and should be practiced. It requires the patient
to recognize early warning symptoms, to carry appropriate medication
and to be trained in its use.
Common
Food
Hymenoptera stings
(e.g. bee, wasp, "jumper ants")
Medication
(e.g. aspirin, NSAIDS, antibiotics, radio contrast, anaesthetic
agents, herbal remedies etc)
Uncommon
Latex Immunotherapy
Exercise Transfusions
Idiopathic Cold urticaria
Tick bites Dialysis membranes
Hormonal Airborne allergen
(domestic & laboratory animals, pollen)
Vasovagal episodes
Hereditary angioedema
Idiopathic urticaria / angioedema
Idiopathic hypovolaemic syndrome
Shock (septic, cardiogenic, haemorraghic)
Neurological syndromes (seizures, strokes)
Flushing syndromes (carcinoid, medullary carcinoma, mastocytosis)
Functional syndromes (panic disorders, globus hystericus, larygospasm)
Miscellaneous (ruptured hydatid cyst, ingestion of scombroid fish,
serum sickness)
Common triggers of anaphylaxis include food, stinging insects
and medication
Exercise and alcohol are common co-factors
Appropriate Management of Anaphylaxis includes:
Identification of triggers and co-factors (where possible)
Identification of patients at risk with a MedicAlert bracelet
Avoidance of medication which may complicate management
Training patients to recognize early warning symptoms, to carry
appropriate medication and to be knowledgeable in its use.
Specialist assessment
