Patch testing in drug allergy.

PURPOSE OF REVIEW: The review intends to clarify understanding of when and how skin patch tests can be used to help drug allergy diagnosis and identify causally relevant drugs. It aims to give an understanding of which clinical patterns of drug reaction are produced by T-lymphocyte-mediated pathomechanisms since these are what are detected by patch tests. It also covers fundamental principles underlying patch test methodology and summarizes clinical patterns and causal drugs for which patch tests have reasonable value to diagnose culprit drugs.

RECENT FINDINGS: A number of recent studies have consolidated evidence that the use of patch tests in drug hypersensitivity diagnosis is not a robust science. The field is bedeviled by the lack of standardized approach to ascertain and define clinical entities in a sufficiently clear way that allows researchers to be confident that patch tests are used appropriately in T-cell-mediated clinical conditions. The literature is confounded by case series including patch tests from conditions which may be the wrong type of test causing the sensitivity of the test system to be measured incorrectly.

SUMMARY: For certain drug eruptions mediated by T cells (exanthemata, acute generalized exanthematous pustulosis, drug rash with eosinophilia and systemic symptoms, erythema multiforme/toxic epidermal necrolysis, fixed drug eruption and symmetrical drug-related intertriginous and flexural exanthem) patch tests can elicit positive responses in a proportion of cases. The test works best with aromatic anticonvulsants and various antibiotics but does not appear to work consistently with a wide range of drugs. A coordinated and systematic research effort is required to resolve inconsistencies to encourage greater utilization of this potentially important diagnostic methodology.