Fixed Drug Eruption (FDE) is a distinctive and often perplexing manifestation of drug hypersensitivity. Diagnosing FDE accurately is crucial for effective management and prevention of future reactions. A recent multicenter study titled “In Situ Patch Test and Repeated Open Application Test for Fixed Drug Eruption: A Multicenter Study” sheds new light on this diagnostic challenge. This study, conducted across 11 dermatology and allergology centers in France, offers a thorough examination of the sequential diagnostic approach involving in situ patch tests (PT), repeated open application tests (ROAT), and drug challenges (DC).
Background
Fixed drug eruption (FDE) is a cutaneous adverse drug reaction characterized by erythematous plaques or blisters that recur at the same site upon re-exposure to the causative drug. It can leave residual pigmentation and, in severe cases, may present as generalized bullous fixed drug reaction (GBFDE).
Objective
The study aimed to evaluate the sensitivity of a standardized allergy workup for diagnosing the cause of FDE, with an emphasis on in situ repeated open application tests (ROATs).
Methods
A retrospective multicenter study analyzed the allergy workup practices for FDE diagnosis across 11 centers in France. The workup involved a three-step process:
- In Situ Patch Tests (PTs): Potential offending medications were applied directly to previously affected skin sites, except in cases of pure mucosal involvement.
- In Situ Repeated Open Application Test (ROAT): If the in situ PT results were negative, the suspected drug was applied daily for 7 days to the same skin area.
- Drug Challenge (DC): This was conducted only if both in situ PT and ROAT were negative. It involved administering the drug under controlled conditions to confirm the diagnosis.
Results
Out of 98 suspected FDE cases, 61 patients (median age 61 years, male-to-female ratio 1.8) with a complete allergy workup were included. The implicated drugs included paracetamol, β-lactams, imidazoles, NSAIDs, iodinated contrast media, and cotrimoxazole, among others.
- In Situ PT: Positive in 17 of 54 cases (31.5%).
- In Situ ROAT: Positive in 14 of 40 cases (35%), with remote reactivation in 4 cases.
- Drug Challenge: Positive in 26 cases.
Study Highlights
The study’s design is commendable for its breadth and depth. By involving multiple centers, the research achieves a level of diversity in its patient sample, enhancing the generalizability of its findings. The sequential allergy workup involving in situ PT, in situ ROAT, and DC is a reliable and safe method for diagnosing the cause of FDE. The sensitivity of in situ tests was over 50%, making them valuable tools in the diagnostic process.
Our Perspectives
This new technique offers several advantages:
- Enhanced Diagnostic Accuracy: Combining the two steps potentially leads to a more definitive diagnosis compared to traditional methods.
- Improved Patient Care: Accurate identification of the culprit medication allows healthcare providers to effectively prevent future reactions and optimize treatment plans.
However, some considerations remain:
- FDE Reactivation: The study noted that in situ ROAT occasionally caused the FDE to reappear in areas beyond the application site. Careful monitoring is necessary.
- Inconclusive Results: Even with both tests, some cases might remain inconclusive, requiring alternative diagnostic measures.
In summary, this research demonstrates a promising new approach to diagnosing FDE by utilizing a sequential workup with in situ patch tests, repeated open application tests, and drug challenges. While these initial results are encouraging, further research with prospective designs and larger, more diverse cohorts is needed for definitive validation and establishment as a standard tool. Additionally, addressing potential biases in the current sample, standardizing test preparations, and delving deeper into areas like remote reactivation management and negative test results would strengthen the study’s findings. Integrating routine histopathological confirmation and long-term patient follow-up data could further solidify the clinical applicability of this method. By refining this approach through future research, we can unlock its potential for improved patient care and FDE management.
