### Date : 2024-06-23 19:30 ### Topic : Skin Patch Test #medicine #dermatology ---- ### Skin Patch (피부첩포검사) Test Overview A **skin patch test** is a diagnostic tool used to identify allergens that cause contact dermatitis, a type of skin inflammation. The test involves applying small amounts of potential allergens to the skin, usually on the back, to observe if any allergic reactions occur. ### Purpose of the Skin Patch Test - **Identify Allergens:** Determines which substances cause allergic skin reactions. - **Diagnose Allergic Contact Dermatitis:** Helps confirm a diagnosis of contact dermatitis and differentiate it from other skin conditions. - **Guide Treatment:** Assists in creating an avoidance plan to reduce exposure to identified allergens. ### Indications for Patch Testing - **Persistent or Recurrent Dermatitis:** Especially when the cause is not obvious. - **Occupational Dermatitis:** Suspected allergies to substances encountered at work. - **Dermatitis Unresponsive to Treatment:** When standard treatments do not resolve the skin condition. - **Atopic Dermatitis with Suspected Allergic Component:** To identify potential triggers. ### Procedure  <Photo from: https://www.healthline.com/health/eczema/eczema-skin-patch-test> **1. Preparation:** - **Patient History:** Detailed history of skin reactions and potential allergen exposures. - **Avoid Medications:** Patients may need to stop taking certain medications (e.g., antihistamines, topical steroids) before the test, as these can interfere with results. **2. Application:** - **Patch Test Kits:** Commercially prepared panels with common allergens (e.g., metals, fragrances, preservatives, rubber chemicals). - **Placement:** The allergens are applied to small patches, which are then placed on the skin, usually on the back. - **Number of Allergens:** Typically, 20-30 allergens are tested at once. **3. Monitoring:** - **Initial Placement:** Patches are left in place for 48 hours, during which the patient must avoid activities that might cause sweating or dislodge the patches. - **First Reading:** After 48 hours, the patches are removed, and the skin is examined for reactions. - **Second Reading:** Another reading is done 72-96 hours after application to check for delayed reactions. ### Interpretation of Results **1. Reaction Types:** - **Negative:** No reaction or minimal redness without itching or swelling. - **Weak Positive (+):** Redness with slight edema (swelling) and possible small vesicles (blisters). - **Strong Positive (++):** Edema, vesicles, and significant redness. - **Extreme Positive (+++):** Intense redness, edema, and large blisters. **2. Common Allergens:** - **Metals:** Nickel, cobalt, chromium. - **Fragrances:** Balsam of Peru, fragrance mix. - **Preservatives:** Formaldehyde, parabens, isothiazolinones. - **Rubber Chemicals:** Thiuram mix, mercaptobenzothiazole. - **Others:** Lanolin, neomycin, epoxy resin. **3. Follow-Up:** - **Positive Reactions:** Indicate an allergy to the specific substance tested. - **Negative Reactions:** No allergy to the tested substances. - **Counseling:** Patients receive guidance on avoiding identified allergens. ### Example Case Study **Patient Profile:** - **Name:** Jee Hoon Ju - **Age:** 35 - **Occupation:** Hairdresser **Medical History:** - Persistent dermatitis on the hands and arms, unresponsive to topical steroids and emollients. - Suspected allergy to hairdressing chemicals. **Procedure:** - **Patch Test Application:** Allergens related to hairdressing, including fragrances, preservatives, and hair dye components, were applied. - **Monitoring:** Patches were left in place for 48 hours, with readings taken at 48 and 72 hours. **Results:** - **Positive Reaction:** Strong positive reaction (+++) to paraphenylenediamine (PPD), a common hair dye ingredient. - **Negative Reactions:** No reaction to other tested allergens. **Diagnosis:** Based on the patch test results, Jee Hoon Ju is diagnosed with allergic contact dermatitis to paraphenylenediamine. **Management:** - **Avoidance:** Advised to avoid products containing PPD and use alternative hair dyes. - **Topical Treatment:** Continued use of topical steroids to manage current dermatitis flare-ups. - **Education:** Provided information on how to read labels and recognize PPD in products. ### Conclusion The skin patch test is a valuable diagnostic tool for identifying specific allergens that cause contact dermatitis. By applying allergens to the skin and observing reactions, healthcare providers can pinpoint the substances responsible for allergic reactions and guide patients on how to avoid them. This test helps in managing and preventing contact dermatitis, improving patients' quality of life.