Skin testing with the suspected compound has been reported to be helpful in determining the cause of cutaneous adverse drug reactions (ADRs), but the value and specificity of these tests need to be determined. In this study, 72 patients with presumed drug eruptions (27 maculopapular, 18 urticarial, seven erythrodermic, nine eczematous, four photosensitivity, three fixed drug eruptions, three with pruritus and one with acute generalized exanthematous pustulosis) were assessed. All had drug patch tests; 46 also had prick tests and 30 had intradermal tests (performed on hospitalized patients using a sterile solution of the suspected drug, diluted sequentially) with immediate and delayed readings. Among these patients, 52 (72%) had a positive skin test reaction, 43%, 24% and 67% in patch, prick and intradermal skin tests, respectively. The results of skin tests varied with the drug tested and with the clinical type of cutaneous ADR, as a significantly higher number of positive patch tests was observed in maculopapular rashes than in urticarial reactions (P = 0.001). This study supports the value of careful sequential drug skin testing in establishing the cause of cutaneous ADR. Guidelines are proposed for performing these tests, and these include the use of appropriate negative control patients to avoid false-positive results.

Skin tests with drugs can be of value in investigating patients who have developed cutaneous adverse drug reactions (CADR), but their specificity and relevance remain to be determined. A false-positive result on skin testing can happen if it is not compared to results in control subjects. When performing intradermal tests (IDT), we have determined the lowest concentrations that induce false-positive results for many drugs, including betalactam antibiotics, cephalosporins, other antibiotics or non-steroidal anti-inflammatory drugs. Some drugs in their commercialized form contain sodium lauryl sulfate and can induce irritation when patch tested as such. When patch tested with colchicine at 10% in pet. or with a Cytotec pill (containing misoprostol) at 30% in pet., respectively, 80% of the 29 and 9 of the 10 negative controls developed false-positive results. Lastly, positive results of patch tests with drugs can be related to contact allergy to one of the components of the commercialized form of the drug, without any relevance to the investigation of a CADR, as observed in 2 cases with iodine or avocado oil.

Dermatologic fungal infections are thought to occur less frequently in children than in adults. This study, performed over a 5-year period, emphasizes the interregional variability of dermatophytes that cause skin and cutaneous apprendageal diseases in children. In northeast France, two-thirds of dermatophytoses are due to zoophilic fungi, while they are most commonly caused by anthropophilic agents in the Paris region and in other countries. The clinical features of pediatric dermatophytoses vary with the age of the child: tinea capitis and tinea corporis are far more frequent before the age of 12 years. After the age of 12, even if these are still quite frequent, tinea pedis and onychomycosis become more common.

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