Photoepicutaneous testing

The effects of various vehicles, the occlusion time and the concentration of the test substances on the phototoxic reactions were studied using the Finn Chamber method in photoepicutaneous testing, with methoxsalen and coal tar as test substances. Petrolatum proved to be a suitable base for methoxsalen and carbowax for coal tar. The optimal concentration of coal tar was 5% and that of methoxalen 0.03-0.05%. The optimal occlusion time for methoxsalen was 1-2 hours and for coal tar 24 hours. It was concluded that in order to obtain the most reliable results, these parameters should be determined separately for every photosensitizing compound to be tested.     

Epicutaneous patch testing

Epicutaneous patch testing is still regarded as the best method of diagnosing allergic contact dermatitis. The present patch test technique is the result of a continuous process of development and improvement since its first application in the late 19th century. During the last decades of the 20th century a lot of effort was put into standardization of materials and methods used in patch testing. Patch tests can be used to confirm a suspected allergic contact dermatitis and either to recommend avoidance of particular products or to recommend alternative products in a particular patient. The true rate of clinically relevant hypersensitivity in positive patch test reactions remains to a great extent unknown. The ideal patch test should cause as few adverse reactions as possible, but a lot of adverse reactions have been described. How-ever, it has to be noted that the overall risk-benefit equation of patch testing is in favor of the benefit, if performed correctly and with the proper indications. A careful history taking and attention to the clinical picture are key actions to facilitate the interpretation of the clinical relevance of the epicutaneous patch test results.     

Merthiolate testing in twins

Positive and negative patch tests to merthiolate occur with the same frequency in monozygotic and dizygotic twin pairs. There is no correlation to strong or weak reactions to primary irritants. Consequently, the positive merthiolate reactions should be considered allergic rather than irritant.     

Patch testing in children

92 children (45 girls, 47 boys), mean age 9.3 years (3-14.75), were referred to the Contact Dermatitis Investigation Unit, Belvidere Hospital, Glasgow, for patch testing during the period 1979–93 for the investigation of allergic contact dermatitis (ACD). The diagnoses at the time of referral were atopic dermatitis (45). non-atopic with localized dermatitis (26), juvenile plantar dermatosis (15), orofacial granulomatosis (2), vaccination reaction (2) and atypical psoriasis (2). In total, there were 55 positive reactions in 30 children. The commonest allergens were metals (18), fragrances (11) and rubber compounds (6). The patient groups with the highest yield of positive patch tests were those patients with atopic dermatitis who had a good history of a precipitating contact factor (4/5), and non-atopic patients with dermatitis of hands and/or feet (7/14). Our findings suggest that allergic contact dermatitis is more common in children than generally appreciated and that patch testing is a practicable and clinically worthwhile procedure in children.     

In vitro allergy testing

Along with the history, skin tests and provocation tests, in vitro test procedures are essential for the adequate care for patients with allergies. While serological investigations of immediate-type allergic reactions primarily detect allergen-specific IgE antibodies, basophil activation tests with different read-out parameters are available for cellular diagnosis of immediate-type reaction patterns. If clinically necessary, further immunological methods (i. e. immunoblots, lymphocyte transformation tests) can be employed. New options are provided by allergen microarray technology, which makes it possible to determine not only the specific antigenic protein but also to analyze different epitopes.     

Patch testing in infants

The aim of this study was to evaluate the frequency of contact sensitization in infancy because very few data on this topic are available in the literature. We patch tested 53 children, ranging in age from 3 months to 2 years, admitted to our allergological outpatient department for eczematous dermatitis with the Italian Research Group on Contact and Environmental Dermatitis standard series. Thirty-nine of the 53 patients were affected by atopic dermatitis. Thirty-two patients (60%) showed positivities to patch tests; 16 of these were polysensitized. Twenty-five of the contact-sensitized children had atopic dermatitis. The haptens responsible for the highest number of positivities were thimerosal and nickel, followed by ammoniated mercury, disperse dyes, fragrances, and preservatives. Our results stress the importance of patch testing patients with atopic dermatitis or suspected contact dermatitis younger than 2 years of age.     

Patch testing with colophony

Colophony (rosin) has been fractionated into 2 parts, an acidic and a neutral fraction. Routine patch testing with neutral components gives positive reactions at a 40% higher frequency than routine patch testing with colophony (20%) (w/w in pet.). A concentration of 60% colophony is suggested for routine patch testing.