Podcast
Questions and Answers
Which condition is least likely to cause permanent changes at the patch test site?
Which condition is least likely to cause permanent changes at the patch test site?
What is the primary risk of not performing patch testing on appropriate dermatitis patients?
What is the primary risk of not performing patch testing on appropriate dermatitis patients?
What is the most common delayed reaction noticed after patch testing?
What is the most common delayed reaction noticed after patch testing?
Which of the following allergens is most commonly associated with anaphylaxis during patch testing?
Which of the following allergens is most commonly associated with anaphylaxis during patch testing?
Signup and view all the answers
What is the recommended strategy for performing patch testing in patients taking immunosuppressive drugs?
What is the recommended strategy for performing patch testing in patients taking immunosuppressive drugs?
Signup and view all the answers
What is the primary purpose of patch testing in diagnosing allergic contact dermatitis (ACD)?
What is the primary purpose of patch testing in diagnosing allergic contact dermatitis (ACD)?
Signup and view all the answers
What components are included in the current T.R.U.E.test?
What components are included in the current T.R.U.E.test?
Signup and view all the answers
Why is expanded patch testing necessary in many patients?
Why is expanded patch testing necessary in many patients?
Signup and view all the answers
How long after patch test removal should a reading typically be performed?
How long after patch test removal should a reading typically be performed?
Signup and view all the answers
Which of the following allergens is NOT included in the T.R.U.E.test?
Which of the following allergens is NOT included in the T.R.U.E.test?
Signup and view all the answers
What is the main difference between the closed-test protocol and the repeat open application test?
What is the main difference between the closed-test protocol and the repeat open application test?
Signup and view all the answers
What is a common recommendation for reading results after patch testing?
What is a common recommendation for reading results after patch testing?
Signup and view all the answers
What is the grading scale used for positive patch test reactions according to Wilkinson and colleagues?
What is the grading scale used for positive patch test reactions according to Wilkinson and colleagues?
Signup and view all the answers
How is an irritant patch test reaction typically characterized?
How is an irritant patch test reaction typically characterized?
Signup and view all the answers
Which of the following allergens is listed as potentially causing pustular irritant reactions?
Which of the following allergens is listed as potentially causing pustular irritant reactions?
Signup and view all the answers
What does a positive patch test result indicate?
What does a positive patch test result indicate?
Signup and view all the answers
What may complicate the evaluation of positive reactions in darker skin types?
What may complicate the evaluation of positive reactions in darker skin types?
Signup and view all the answers
Which possible outcome follows the initial patch test reading?
Which possible outcome follows the initial patch test reading?
Signup and view all the answers
What type of reactions are considered as 'questionable' in patch testing?
What type of reactions are considered as 'questionable' in patch testing?
Signup and view all the answers
What does current relevance of a positive patch test result indicate?
What does current relevance of a positive patch test result indicate?
Signup and view all the answers
What characterizes an irritant reaction compared to an allergic reaction?
What characterizes an irritant reaction compared to an allergic reaction?
Signup and view all the answers
Study Notes
Patch Testing for Allergic Contact Dermatitis (ACD)
- Patch testing is the gold standard for identifying allergens causing ACD.
- The T.R.U.E. test (SmartPractice, Denmark) is an epicutaneous patch test system approved for adults (≥18).
- Originally containing 23 allergens and 1 control, the T.R.U.E. test now has 3 panels with a total of 35 allergens and 1 blank control.
- Expanded patch testing, including testing with patient items and pediatric patients, is considered standard practice in ACD diagnosis (off-label).
- The T.R.U.E. test misses some commonly positive allergens, including fragrance mix II, lanolin, and several others.
- Increasing the number of allergens tested improves the sensitivity of patch testing. A standard 28 allergen series identifies allergens for less than one-third of patients.
- A standard closed-test protocol uses occluded patches, 48-hour removal, and a 72- or 96-hour read. An early read may also be performed at 48 hours.
- A 20-minute interval is typically sufficient after patch removal before reading to minimize tape irritation effects. Certain cases may require prolonged readings (7-10 days).
- Delayed reactions (metals, antibiotics, corticosteroids) are significant.
- Repeat open application testing applies substances twice daily (1–3 weeks) for leave-on products. Semiopen testing is suitable for liquids.
- Patch test results are graded as positive, negative, questionable, or irritant.
- The International Contact Dermatitis Research Group recommends a + to +++ scoring system.
-
- = weak nonvesicular reaction, palpable erythema.
- ++ = strong edematous or vesicular reaction.
- +++ = extreme bullous or ulcerative reaction.
- ?/+– indicates very weak or questionable reactions with faint or macular nonpalpable erythema.
- IR = irritant reactions.
-
- Irritant patch test reactions (erythematous, sharply demarcated, discretely scaly) are associated with fragrance mix, cocamidopropyl betaine, iodopropynyl butylcarbamate, glutaraldehyde, and thiuram mix.
- Purpuric reactions (petechial hemorrhage) can be associated with cobalt; pustular reactions with metallic salts (potassium dichromate, cobalt, nickel, gold, copper).
- Other allergens with potential irritant reactions include various preservatives, rubber allergens, fragrance chemicals, foaming agents, and emulsifiers.
- Distinguishing allergic from irritant reactions can be challenging but there are useful clues. Strong irritant reactions appear early and resolve quickly; strong allergic reactions spread slowly and develop into eczema.
- Darker skin types may have less obvious erythema during patch testing, needing careful palpation for edema and papules/vesicles. A fluorescent marking ink is best for marking and locating patch test sites on dark skin.
- A positive patch test indicates sensitization but not necessarily ACD. Relevance of a positive result is assessed (preliminary, final, current, past, doubtful) for clinical relevance.
- Patch testing is generally safe, with common side effects such as itching at the reaction site and tape irritation. Post-inflammatory changes, infections, scarring, persistent reactions, induction of dermatitis flareups, sensitization, and anaphylaxis are less common.
- Post inflammatory hypopigmentation/hyperpigmentation occurs; hyperpigmentation is more likely in darker skin tones. Sunlight exposure can worsen hyperpigmentation.
- Persistent reactions (>30 days) may be related to medications like gold.
- Patch testing can be used to induce flare-ups of pre-existing dermatoses. Patch testing should ideally be done in patients without active dermatitis.
- Active sensitization may occur (new reactions 10–21 days post-testing), often appearing in strong sensitizers.
- Anaphylaxis is a very rare but possible complication in those with known type I hypersensitivity reactions.
- Failure to test appropriate patients is the greatest hazard, potentially leading to repeated ACD episodes.
- Approximately 72 million people in the US have ACD and it's the third-most common reason for dermatological consultations.
- Systemic immunosuppressant medications may confound patch testing results; reducing the dose is recommended if unavoidable.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
This quiz delves into the principles of patch testing and its role in diagnosing allergic contact dermatitis (ACD). Learn about the T.R.U.E. test, its panels, sensitivity, and common allergens missed in standard testing. Understand the protocols and best practices in allergen identification.
