Clinical Presentation and Differential Diagnosis

The severity of the hypersensitivity reaction is classified into four grades (see Table 4.3): IgE- or non-IgE-mediated reactions and anaphylactoid or anaphylactic reactions, respectively, cannot be differentiated clinically.

The most important clinical signs are (Chiu and Kelly 2005):

Cutaneous reactions (erythema, urticaria ) and soft tissue swelling (e.g., eyelids, lips) • Hypotension and tachycardia

Table 4.3. Severity of immediate hypersensitivity reactions

Grade Symptoms

Grade 1 Only cutaneous signs: diffuse erythema, urticaria Grade 2 Same as grade 1 + nausea, cough, dyspnea, tachycardia, hypotension Grade 3 Same as grade 2 + vomiting, diarrhea, broncho-

spasm, cyanosis, shock Grade 4 Cardiovascular arrest (apparent death)

Histamine

Leukotrienes

Histamine

Leukotrienes

Tryptase

Histamine

After Ring and Messmer (1977)

• Respiratory symptoms (cough, dyspnea, broncho-spasm, laryngeal edema, and cyanosis)

• Gastrointestinal reactions (nausea, vomiting, diarrhea)

• Neurological reaction (loss of consciousness)

Other diagnoses that might mimic anaphylaxis should be considered, since there are several conditions that can also cause abrupt and dramatic patient collapse. Acute reactions should be excluded if possible; these include vasodepressor (vasovagal) reactions, acute anxiety (e.g., panic attack or hyperventilation syndrome), myocardial dysfunction, pulmonary embolism, aspiration, and hypoglycemia.

The clinical presentation of an anaphylactic/ana-phylactoid reaction can differ greatly in each patient; it is also very much dependent on the route of allergen exposure, the rate of absorption, and the grade of sensitivity to the allergen. The symptoms may appear only seconds or minutes after the contact with the allergen.

In more than 90 % of all cases, cutaneous symptoms such as pruritus, flush, or erythema happen prior to systemic reaction. However, cutaneous manifestations might be delayed or absent in rapidly progressive ana-phylactic shock.

Obstruction of the pulmonary system is very common and can be life threatening. The reason maybe ex-trathoracic (caused by swelling of the larynx or pharynx) or intrathoracic (caused by obstruction of the bronchi). Most often the swelling of the larynx is the cause of death in anaphylactoid reactions and starts with hoarseness, wheeze, and stridor. As in acute shock, edema of the larynx may be the only symptom of anaphylaxis.

Gastrointestinal symptoms such as nausea, vomiting, diarrhea, abdominal pain, bowel urgency are caused by disturbance of the permeability of the gastrointestinal system and additionally by the hypermo-bility of the bowels due to stimulation of histamine receptors.

The exact mechanism of hemodynamic reactions is not fully understood. Leading symptoms are hypovole-mia due to vasodilatation and fluid shift into the inter-stitium, and tachycardia as well as decreased cardiac filling pressure.

It is unknown whether cerebral signs such as dizziness, syncope, cramps, and unconsciousness are caused by cerebral lack of perfusion or a direct effect of the mediators.

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