In this episode of Derms and Conditions, host James Q. Del Rosso, DO, welcomes Walter Liszewski, MD, for a discussion on the role of patch testing in patients with atopic dermatitis (AD), from the fundamentals of testing and interpretation to its application in patients with persistent or incomplete responses to therapy.

Dr Liszewski explains why allergic contact dermatitis is frequently overlooked in dermatology practice and how it commonly overlaps with AD and irritant contact dermatitis. Because these conditions often appear clinically similar, Dr Liszewski explains that, unlike AD or irritant contact dermatitis, allergic contact dermatitis has a diagnostic test available, making patch testing an important tool when the underlying cause of eczema is uncertain.  

The conversation explores when patch testing should be considered in light of the absence of formal guidelines, with Dr Liszewski sharing his practical approach to identifying patients who may benefit from testing and how it can fit into the management of patients who continue to experience residual eczema despite advanced therapies. He also discusses the different reasons biologic-treated patients may have persistent disease and how patch testing can help distinguish allergic contact dermatitis from a more complex inflammatory phenotype.

Dr Liszewski reviews practical considerations for preparing patients for patch testing, including which medications should be discontinued beforehand and which can generally be continued. He explains why he typically does not stop biologic therapy before testing, while outlining situations in which temporary interruption may be appropriate. The discussion also covers newer molecular testing that may provide additional information in difficult cases and introduces the "paraben paradox," an important concept illustrating how impaired skin barrier function can influence allergic responses.

Tune in to the episode to gain a clearer understanding of when patch testing should be considered in patients with AD, learn how to approach patients with persistent or partial treatment responses, and learn practical considerations for preparing patients and optimizing test accuracy.