Ask about contact with known allergens (i.e., nickel, fragrances, neomycin, and poison ivy/oak).
- Nickel exposure is often related to the wearing of rings, jewelry, and metal belt buckles (Figures 146-3, 146-4, 146-5, and 146-6).
- Fragrances in the forms of deodorants and perfumes (Figure 146-7).
- Neomycin applied as a triple antibiotic ointment by patients (Figures 146-8 and 146-9).
- Poison ivy/oak in outdoor settings. Especially ask when the distribution of the reaction is linear (Figures 146-10 and 146-11).
- Ask about occupational exposures, especially solvents. For example, chemicals used in hat making can cause ICD on the hands (Figure 146-2).
- Tapes applied to skin after cuts or surgery are frequent causes of CD (Figure 146-12).
- If the CD is on the feet, ask about new shoes (Figures 146-13 and 146-14).
Patient moved up his ring to show the allergic contact dermatitis secondary to a nickel allergy to the ring. (With permission from Milgrom EC, Usatine RP, Tan RA, Spector SL. Practical Allergy. Philadelphia, PA: Elsevier, Inc; 2004.)
Allergic contact dermatitis to the metal in the bellybutton ring of a young woman. (Courtesy of Richard P. Usatine, MD.)
Allergic contact dermatitis to the metal in the belt buckle causing erythema, scaling, and hyperpigmentation. (Courtesy of Richard P. Usatine, MD.)
A 12-year-old girl with atopic dermatitis and allergy to the metal in her pants' fastener and metal belts when she wears them. (Courtesy of Richard P. Usatine, MD.)
Allergic contact dermatitis to the fragrance in a new deodorant. (With permission from Milgrom EC, Usatine RP, Tan RA, Spector SL. Practical Allergy. Philadelphia, PA: Elsevier, Inc; 2004.)
Allergic contact dermatitis to neomycin applied to the leg of a young woman. Her mom gave her triple antibiotic ointment to place over a bug bite with a large nonstick pad. The contact allergy follows the exact size of the pad and only occurs where the antibiotic was applied. (Courtesy of Richard P. Usatine, MD.)
Allergic contact dermatitis to a neomycin containing topical antibiotic on the breasts. This woman applied this medicine to treat her breast discomfort that began when her breastfeeding baby developed thrush. (Courtesy of Jack Resneck, Sr., MD.)
A linear pattern of allergic contact dermatitis from poison ivy. (Courtesy of Jack Resneck, Sr., MD.)
Multiple lines of vesicles from poison oak on the arm. (With permission from Milgrom EC, Usatine RP, Tan RA, Spector SL. Practical Allergy. Philadelphia, PA: Elsevier, Inc; 2004.)
Allergic contact dermatitis to the tape used after an abdominal hysterectomy. (With permission from Milgrom EC, Usatine RP, Tan RA, Spector SL. Practical Allergy. Philadelphia, PA: Elsevier, Inc; 2004.)
Allergic contact dermatitis from new shoes. This is the typical distribution found on the dorsum of the feet. (With permission from Milgrom EC, Usatine RP, Tan RA, Spector SL. Practical Allergy. Philadelphia, PA: Elsevier, Inc; 2004.)
A 25-year-old man with allergic contact dermatitis to a chemical in his boots. His boots were higher but he cut them down to try to alleviate the discomfort coming from the boots higher on his leg. (With permission from Milgrom EC, Usatine RP, Tan RA, Spector SL. Practical Allergy. Philadelphia, PA: Elsevier, Inc; 2004.)
A detailed history of products used on the skin may reveal a suspected allergen. In Figure 146-15, this truck driver was using baby wipes to clean his skin during long drives. Patch testing ultimately revealed that he was allergic to one of the ingredients in those wipes.
A 49-year-old truck driver developed pruritic erythematous eruption on his arms and trunk that persisted for 1 year despite various treatments. Patch testing ultimately revealed that he was allergic to isothiazolinone. He went home and discovered this was one of the ingredients in the baby wipes he used to clean his skin during long drives. His allergic contact dermatitis resolved once he stopped using the wipes. (Courtesy of Richard P. Usatine, MD.)
All types of CD have erythema. Although it is not always possible to distinguish between ICD and ACD, here are some features that might help:
- Location—usually the hands.
- Symptoms—burning, pruritus, pain.
- Dry and fissured skin (Figure 146-2).
- Indistinct borders.
Both ICD and ACD may be complicated by bacterial superinfection showing signs of exudate, weeping, and crusts.
Toxicodendron (Rhus) dermatitis (poison ivy, poison oak, and poison sumac) is caused by urushiol, which is found in the saps of this plant family. Clinically, a line of vesicles can occur from brushing against one of the plants. Also, the linear pattern occurs from scratching oneself and dragging the oleoresin across the skin with the fingernails (Figures 146-10 and 146-11).
Systemic CD is a rare form of CD seen after the systemic administration of a substance, usually a drug, to which topical sensitization has previously occurred.6
The diagnosis is most often made by history and physical examination. Consider culture if there are signs of superinfection and there is a concern for methicillin-resistant Staphylococcus aureus (MRSA). The following tests may be considered when the diagnosis is not clear.
- KOH preparation and/or fungal culture if tinea is suspected.
- Microscopy for scabies mites and eggs.
- Latex allergy testing—This type of reaction is neither ICD (nonimmunologic) nor ACD. The latex allergy type of reaction is a type I, or immunoglobulin (Ig)E-mediated response to the latex allergen.
- Patch testing—Common antigens are placed on the skin of a patient. The T.R.U.E. Test comes in three tape strips that are easy to apply to the back (Figure 146-16). There is no preparation needed to test for the 29 common allergens embedded into these strips (Table 146-1 for a list of the 29 allergens). The strips are removed in 2 days and read at that time and again in 2 more days (Figure 146-17). The T.R.U.E. Test website provides detailed information on how to perform the testing and how to counsel patients about the meaning of their results. Any clinician with an interest in patch testing can easily perform this service in the office.
- A metaanalysis of the T.R.U.E. Test shows that nickel (14.7% of tested patients), thimerosal (5.0%), cobalt (4.8%), fragrance mix (3.4%), and balsam of Peru (3.0%) are the most prevalent allergens detected using this system.5
- Critics of the T.R.U.E. Test state that it misses other important antigens. There are a number of dermatologists who create their own more extensive panels in their office. If the suspected allergen is not in the T.R.U.E. Test, refer to a specialist who will customize the patch testing. Also, personal products, such as cosmetics and lotions, can be diluted for special patch testing.
- A metaanalysis of children patch tested for ACD showed the top five allergens to be nickel, ammonium persulfate, gold sodium thiosulfate, thimerosal, and toluene-2,5-diamine (p-toluenediamine).7 Only two of these five allergens are in the T.R.U.E. Test, so it may be best to not use this standardized patch testing for children.
- Once the patch test results are known, it is important to determine if the result is “relevant” to the patient's dermatitis. One method for classifying clinical relevance of a positive patch test reaction is: (a) current relevance—the patient has been exposed to allergen during the current episode of dermatitis and improves when the exposure ceases; (b) past relevance—past episode of dermatitis from exposure to allergen; (c) relevance not known—not sure if exposure is current or old; (d) cross-reaction—the positive test is a result of cross-reaction with another allergen; and (e) exposed—a history of exposure but not resulting in dermatitis from that exposure, or no history of exposure but a definite positive allergic patch test.6
- Punch biopsy—When another underlying disorder is suspected that is best diagnosed with histology (e.g., psoriasis).
The T.R.U.E. Test is an easy-to-use standardized patch test that is applied to the back using 3 tape strips to test for 36 common allergens. Extra hypoallergenic tape is applied to keep the strips from peeling off for 2 days. (Courtesy of Richard P. Usatine, MD.)
Table 146-1 Allergens in T.R.U.E. Test (Patch Test for Contact Dermatitis) ||Download (.pdf)
Table 146-1 Allergens in T.R.U.E. Test (Patch Test for Contact Dermatitis)
Balsam of Peru
p-tert-Butylphenol Formaldehyde Resin
Black Rubber Mix
Cl+ Me− Isothiazolinone (MCI/MI)
Gold sodium thiosulfate
Disperse blue 106
This positive patch test result for nickel shows small vesicles on an erythematous base. The T.R.U.E. Test reading strip is held against the skin to identify the positive antigen. (Courtesy of Richard P. Usatine, MD.)