Patch Testing for ACD Overview

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Questions and Answers

What is meant by 'doubtful relevance' in patch testing?

It suggests that the patient is allergic to multiple allergens.

It indicates a strong allergic reaction to the test substance.

It refers to the absence of identifiable exposure source. (correct)

It is used to describe positive test reactions that fade quickly.

Which of the following is the most common side effect of patch testing?

Persistent patch test reactions.

Induction of dermatitis flares.

Anaphylaxis.

Itching at the site of positive test reactions. (correct)

What can lead to hyperpigmentation at the patch test site?

Immediate contact with cold water following the test.

Using topical corticosteroids too soon after testing.

Reapplication of the adhesive tape used in testing.

Prolonged exposure to sunlight after test removal. (correct)

Which situation is likely to minimize the risk of inducing a dermatitis flare during patch testing?

Testing patients without current active dermatitis. Signup and view all the answers

What is a potential consequence of failure to patch test appropriate dermatitis patients?

It may result in repeated episodes of avoidable contact dermatitis. Signup and view all the answers

What is the primary purpose of the T.R.U.E.Test?

To identify allergens causing allergic contact dermatitis Signup and view all the answers

How many allergens are currently included in the T.R.U.E.Test?

35 allergens plus 1 blank control Signup and view all the answers

Which of the following allergens is NOT included in the T.R.U.E.Test?

Fragrance mix II Signup and view all the answers

What is a significant benefit of expanded patch testing?

It improves sensitivity by identifying more allergens Signup and view all the answers

What is the standard protocol for conducting a patch test with the T.R.U.E.Test?

Allergens are applied and removed after 48 hours, with a final read at 72 or 96 hours Signup and view all the answers

Why might metals, antibiotics, and corticosteroids produce delayed reactions in patch testing?

They often require more time to show reactions Signup and view all the answers

What distinguishes the repeat open application test from the standard closed-test patch method?

It involves applying a substance twice a day for 1 to 3 weeks Signup and view all the answers

What is the purpose of the semiopen patch test protocol?

To test liquid products with irritant potential. Signup and view all the answers

How are positive results from patch tests graded according to the Wilkinson scale?

<ul> <li>is weak, ++ is strong, +++ is extreme.</li> </ul> Signup and view all the answers

What characterizes a typical irritant reaction in patch testing?

Erythematous reactions with well-defined margins. Signup and view all the answers

What type of reaction is characterized by petechial hemorrhage in patch testing?

Purpuric reaction associated with cobalt chloride. Signup and view all the answers

What is a common allergen that produces marginal irritant reactions?

Glutaraldehyde. Signup and view all the answers

In patch testing, how is a questionably weak or faint reaction recorded?

With a question mark ( +/– ). Signup and view all the answers

What distinguishes irritant reactions from allergic reactions in terms of their pattern during testing?

Irritant reactions appear early and resolve quickly, while allergic reactions are slow to develop and often persist. Signup and view all the answers

Which of the following is true about evaluating patch test reactions in darker skin types?

Palpation of the test site can help identify allergic reactions. Signup and view all the answers

What defines 'current relevance' in the context of patch test results?

The allergen is among the chemicals the patient is currently exposed to. Signup and view all the answers

Which of the following best describes thimerosal in relation to patch testing?

It rarely causes dermatitis despite frequent positive patch test reactions. Signup and view all the answers

Study Notes

Patch Testing for Allergic Contact Dermatitis (ACD)

Patch testing is the gold standard for identifying ACD allergens.
The T.R.U.E. Test, introduced in 1995, is an FDA-approved epicutaneous patch test system for adults.
The T.R.U.E. test system initially had 23 allergens and a control; now, it has 3 panels with 35 allergens and a blank control.
Nonstandard/expanded patch tests, including testing with patient products and pediatric patients, are common.
The T.R.U.E. test omits some of the 30 most common positive allergens (fragrance mix II, lanolin, etc).
More allergens tested generally increases the sensitivity of patch testing.
Standard patch tests place allergens on the back under occlusion, removed at 48 hours, and read again at 72/96 hours.
Preliminary readings at 48 hours are sometimes done, but allow enough time for tape irritation to subside. (20 minutes usually sufficient).
Delayed reactions (metals, antibiotics, corticosteroids) may take longer to show.

Patch Test Protocols

Standard closed test protocols are used for commercially available standardized allergens and patient products.
Repeat open application protocols are used to test leave-on products and can last 1-3 weeks.
Semiopen patch testing is for liquid products by applying to skin and allowing them to dry.
Test substance is measured in 1 cm2.

Patch Test Reading and Interpretation

Patch test results are recorded as positive, negative, questionable, or irritant.
Positive reactions are graded (Wilkinson scale): + (weak, non-vesicular), ++ (strong, edematous/vesicular), +++ (extreme, bullous/ulcerative).
Questionable reactions (faint/macular erythema): +/-.
Irritant reactions (IR) have distinct characteristics (erythematous, sharp margins, discrete scaling). Fragrance mix, cocamidopropyl betaine, etc. are frequent irritant triggers.
Purpuric (petechial hemorrhage) is a specific irritant reaction from cobalt chloride.
Pustular reactions are a sign of irritant reaction associated with metals (potassium dichromate, cobalt etc).
Some allergens (formaldehyde, benzalkonium chloride, certain fragrances) have mild irritant potential and should be evaluated cautiously.
Strong irritant reactions appear early and disappear quickly.
Strong allergic reactions spread, disappear more gradually, and show a more eczematous pattern.

Patch Testing in Different Skin Types

Reactions may be harder to evaluate in darker skin types (Fitzpatrick V/VI) due to less obvious erythema; edema & papules/vesicles are still often visible.
Palpation helps detect reactions.
Fluorescent marking inks (yellow highlighter) and Wood light are best for marking patch tests in dark skin types.

Relevance of Positive Patch Test Results

A positive patch test indicates sensitization, but not necessarily ACD.
Establishing relevance (importance to the patient's dermatitis) is a challenge.
Relevance can be preliminary, current, past, or doubtful.
Definitive relevance occurs with a positive use test or suspected object/product patch test.
Relevance is judged at follow-up visits after avoidance.

Patch Test Safety and Side Effects

Patch testing is generally safe.
Common side effects: itching at positive reaction sites, tape irritation/pruritus.
Less common effects: post-inflammatory changes, infections, scarring, persistent reactions, flare-ups, sensitization, and rarely anaphylaxis.
Hyperpigmentation is common in darkly pigmented persons and usually fades with time.
Photosensitivity to allergens with direct light exposure can occur.

ACD Burden and Patch Testing Benefits

ACD is the third most common consultation reason for dermatologists and a common reason for primary care doctor visits.
Estimated burden is 72 million people in US with ACD.
16% of chronic eczema patients may benefit from patch testing.
Patch testing is helpful in identifying causes of chronic recalcitrant eczema.
Approximately 2.2 million US patients could benefit from patch testing annually.

Patch Testing Considerations in Patients on Immunosuppressive Drugs

Systemic drugs that suppress T-cell responses interfere with patch testing.
Testing should be done when patients are off these drugs (prednisone, cyclosporine).
If this is not possible, minimize the dose.

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Description

This quiz covers the fundamentals of patch testing for allergic contact dermatitis (ACD). It includes details on the T.R.U.E. Test, its development, common practices, and the variety of allergens involved. Understand the importance of this testing in diagnosing ACD effectively.