PubMed · 8022560
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E A McConnell. 1994. What's wrong with this patient? Identifying a rash.. https://doi.org/10.1097/00152193-199407000-00016
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While the frequency of patch test reactivity to many cosmetic allergens has decreased over the last 20 years, we have previously shown that in our clinic, the patch test reactivity to p-phenylenediamine (PPD) has remained stubbornly high between 2.5% and 4.2% in the years when patch testing was performed with 1% PPD. Further retrospective analysis of the PPD patch test frequency over the last 6 years shows an increasing rate of PPD patch test frequency, showing an upward linear trend. This increasing trend cannot be fully explained by any increase in patch testing of Southern Asian patients or of sensitization caused by PPD exposure from 'temporary henna tattoos'. An alternative explanation may be the increasing use of permanent hair dyes.
The elicitation of a positive patch test reaction in a given individual depends upon the dose of the sensitizer applied, the patch test technique and the occlusion time. The dose is determined by the concentration and volume/amount of test preparation applied. If the same amount/volume of a test preparation is applied all the time with the same test technique (same area of skin) and occlusion time, it is appropriate to use concentration as a dose parameter. Most contact sensitizers are incorporated in petrolatum (pet.). With pet. as vehicle, it is impossible to repeatedly apply an exact volume/amount. This study was performed to investigate the inter- and intra-individual variation of pet. preparation applied at patch testing by 3 technicians. Weighing demonstrated that the 3 technicians had about the same precision in their pet. application. The investigation demonstrates that there is both an inter-individual (statistically significant) and intra-individual variation in the amounts of pet. applied at patch testing for the 3 technicians. Presently, there is no recommendation on what amount of pet. preparation to apply, which merits a decision to be taken based on thorough investigations on the appropriate volumes of pet. preparation to be applied in various patch test systems.
Contact dermatitis may be either irritant, allergic or both. The differential diagnosis is based on information from the patient, nature and concentration of chemicals involved and clinical examination. In case of suspicion of allergic contact dermatitis, the search for the responsible allergen(s) is built on patch testing. Positive patch test results, the current and/or past relevance of which has to be assessed, are confirmative. Additional tests, such as the repeated open application test, are sometimes recommended. Treatment which is symptomatic, is mainly based upon corticosteroids, either local or systemic; efficacy is rather limited. By any means, it cannot be substituted to the eviction of allergens. Primary and secondary prevention are linked with the complete eviction of allergens, but this caveat can be attenuated in some circumstances.