Clinical Features of Allergies

Clinical manifestations of an allergic reaction are dependent upon the nature of the response, the antigenic challenge and the individual’s allergic predisposition. Early symptoms and signs of a type I (immediate) hypersensitivity reaction include wheezing, breathlessness, sneezing, runny eyes, itching and urticaria, which typically occur within a few minutes to an hour. As the reaction progresses, bronchospasm, acute hypotension and angioedema of the face and laryngopharynx may result in life-threatening anaphylactic shock (Table 17.4).

Contact allergy (type IV delayed hypersensitivity), being a T-cell-mediated process, is characterized by local inflammation at the allergen contact site (skin or mucous membrane), and is usually slower and less profound. Metals, disinfectants, rubber, detergents and bonding agents can cause allergic contact (and irritant contact) dermatitis. Rashes are seen in many allergies (Fig. 17.3).

General Management of Allergies

Physical factors (thermal stimuli, sunlight, water, pressure) and drugs may also release histamine in susceptible individuals and cause features similar to allergies. For example, morphine can directly trigger mast cell histamine release and occasionally causes anaphylactoid reactions.

Diagnosis of an allergy is based on clinical history and presentation, including a family history of allergy; skinprick or patch testing to identify contact allergens using a battery of test allergens (European Standard Contact Dermatitis Testing Series; Table 17.5); or an elimination diet to identify food allergens. Patch testing is usually carried out with Finn chambers on Scanpor, a non-woven adhesive skin-friendly tape that contains no colophony. Assays of serum IgE levels (PRIST: paper radio-immunosorbent test) and serum specific IgE antibodies (RAST: radioallergosorbent test) can help. In the RAST, purified extracts of a range of allergens are coupled to cellulose or paper discs to which the patient’s serum is applied. Its ability to react with one or more of these allergens is tested by adding rabbit anti-IgE labelled with radioactive iodine. The level of radioactivity then indicates the levels of specific IgE antibodies.

The British Standard Series of 12 allergens, used in addition to those already in the European Standard Series, includes carba mix, ethylenediamine, cetearyl alcohol, 2-bromo-2-nitropane-1,3-diol, diazolidinyl urea, chlorocresol, fusidic acid, imidazolidinyl urea and chloroxylenol.

The Dental Series typically includes amalgam, amalgam alloying metals, ammoniated mercury, ammonium tetrachloroplatinate, benzoyl peroxide, bisphenol A (Bis-GMA), diurethane dimethacrylate, ethylene glycol dimethacrylate, eugenol, 2-hydroxyethyl methacrylate (2-HEMA), hydroquinone, menthol, methyl methacrylate, palladium chloride peppermint oil, potassium dicyanoaurate, N,N-dimethyl-p-toluidine, sodium thiosulfatoaurate and triethylene glycol dimethacrylate.

No tests, however, can reliably predict the possibility of allergic or anaphylactic reactions. Many cases of ‘local anaesthesia (LA) allergy’ represent untoward events, such as the unintended intravenous injection of the drug, while many cases of ‘food allergy’ are of food intolerance or occasionally food poisoning only. Supposed phenomena such as systemic ‘allergy’ to amalgam restorations, ‘candida syndrome’ and ‘total allergy syndrome’ are myths.

Medications such as antihistamines or antidepressants that interfere with allergy tests must be stopped from 2 days to 6 weeks or more before testing. Resuscitation facilities must be available during allergy testing, since anaphylactic reactions can occasionally follow intradermal skin test doses, particularly of penicillin. The test procedure includes a positive control (usually histamine), a negative control – a solution without allergens, and then the test – the various suspect allergens. If the test substance provokes an allergic reaction, a raised, red, itchy wheal may develop within about 20 minutes; in general, the larger the reaction, the more sensitive is the patient. A negative skin test means that the patient is not allergic to that particular allergen. A complication of skin testing is that it can induce sensitivity to the test compound.

To avoid future allergic reactions, known allergens should be avoided, which is easier said than done, since sensitive individuals may react to minute traces and allergens can be present in the most unexpected places (more likely in commercially prepared foods and drinks than in natural products).

Individuals with a complex history of allergy should be referred to a specialist allergy clinic for careful assessment and management. Treatments include drugs to block allergic mediators, or the activation of cells and degranulation (Table 17.6). These include antihistamines, corticosteroids and cromoglicate. Antileukotrienes (leukotriene receptor antagonists, e.g. montelukast or zafirlukast) are also effective. Intravenous injection of monoclonal anti-IgE antibodies (omalizumab), which bind to free and B-cell–associated IgE, causes their destruction. Immunotherapy by desensitization or hyposensitization is a treatment in which the patient is gradually vaccinated with progressively larger doses of the responsible allergen for at least a year – but this is potentially hazardous, as it can induce anaphylaxis.

Patients who have had serious allergic reactions are also usually advised always to carry adrenaline (epinephrine) with them, for subcutaneous self-administration in the event of a reaction (e.g. EpiPen; see below).

There is no reliable evidence that supports the use of alternative medicine in the control of allergies.

Anaphylaxis

General aspects

Anaphylaxis is a severe life-threatening type I hypersensitivity reaction, which may affect up to 15% of the population. Hyper-IgE syndromes predispose to anaphylaxis and it is caused mainly by food, drugs, latex and insect stings (Table 17.7).

Clinical features

Bronchospasm, acute hypotension and angioedema of the face and laryngopharynx are the critical features, but there may also be flushing, dizziness and urticaria. The condition may progress to arrhythmias or cardiac arrest. The time to onset is usually indicative of the severity of the reaction (i.e. the more rapid the onset, the more severe the reaction). Most reactions occur within seconds to 30 minutes of exposure to the responsible precipitant.

General management

People at risk must avoid the allergens responsible and carry adrenaline (epinephrine) for immediate use to inject into the outer thigh muscle. Patients should carry 2 EpiPens® with them because>35% of patients may require more than one adrenaline dose and up to 20% of patients will go on to develop a biphasic anaphylactic response sometimes hours later (Fig. 17.4).