Chapter 146. Contact Dermatitis

A 38-year-old woman twisted her right ankle and applied a Chinese medicine patch to relieve the pain. The following day the patient developed a severe contact dermatitis (CD) with many small vesicles (<5 mm) and bullae (>5 mm) (Figure 146-1). The erythema had a well-demarcated border and was traced by the doctor's pen. Cold compresses and a high potency topical steroid were prescribed. When the patient showed little improvement a 2-week course of oral prednisone was given starting with 60 mg daily and tapering down to 5 mg daily. The patient responded rapidly and the CD fully resolved.1,2

CD is a common inflammatory skin condition characterized by erythematous and pruritic skin lesions resulting from the contact of skin with a foreign substance. Irritant contact dermatitis (ICD) is caused by the non-immune-modulated irritation of the skin by a substance, resulting in a skin changes. Allergic contact dermatitis (ACD) is a delayed-type hypersensitivity reaction in which a foreign substance comes into contact with the skin, and upon reexposure, skin changes occur.3

• Some of the most common types of CD are secondary to exposures to poison ivy, nickel, and fragrances.4
• Patch testing data indicate that the five most prevalent contact allergens out of more than 3700 known contact allergens are nickel (14.3% of patients tested), fragrance mix (14%), neomycin (11.6%), balsam of Peru (10.4%), and thimerosal (10.4%).5
• Occupational skin diseases (chiefly CD) rank second only to traumatic injuries as the most common type of occupational disease. Chemical irritants such as solvents and cutting fluids account for most ICD cases. Sixty percent were ACD and 32% were ICD. Hands were primarily affected in 64% of ACD and 80% of ICD4 (Figure 146-2).

• CD is a common inflammatory skin condition characterized by erythematous and pruritic skin lesions resulting from the contact of skin with a foreign substance.
• ICD is caused by the non-immune-modulated irritation of the skin by a substance, resulting in a skin rash.
• ACD is a delayed-type hypersensitivity reaction in which a foreign substance comes into contact with the skin, and is linked to skin protein forming an antigen complex that leads to sensitization. Upon reexposure of the epidermis to the antigen, the sensitized T cells initiate an inflammatory cascade, leading to the skin changes seen in ACD.

History

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).

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.

Clinical Features

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:

• ICD:
  • Location—usually the hands.
  • Symptoms—burning, pruritus, pain.
  • Dry and fissured skin (Figure 146-2).
  • Indistinct borders.
• ACD:
  • Location—usually exposed area of skin, often the hands.
  • Pruritus is the dominant symptom.
  • Vesicles and bulla (Figures 146-1 and 146-8).
  • Distinct angles, lines, and borders (Figures 146-8, 146-9, 146-10, 146-11, and 146-12).

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

Laboratory Studies

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).

• Atopic dermatitis is usually more widespread than CD. There is often a history of other atopic conditions, such as allergic rhinitis and asthma. There may be family history of allergies. However, persons with atopic dermatitis are more prone to CD (Figure 146-6; Chapter 145, Atopic Dermatitis).
• Dyshidrotic eczema—Seen on the hands and feet with tapioca vesicles, erythema, and scale. Although this is not primarily caused by contact to allergens, various irritating substances can make it worse (see Chapter 147, Hand Eczema).
• Immediate IgE contact reaction (e.g., latex glove allergy)—Immediate erythema, itching, and possibly systemic reaction after contact with a known (or suspected) allergen.
• Fungal infections—A dermatophyte infection that can closely resemble CD when it occurs on the hands and feet. Tinea pedis is usually seen between the toes, on the soles or on the sides of the feet. CD of the feet is often on the dorsum of the foot and related to rubber or other chemicals in the shoes (Figures 146-13 and 146-14; Chapter 140, Tinea Pedis).
• Scabies on the hands can be mistaken for CD. Look for burrows and for the typical distribution of the scabies infestation to distinguish this from CD (see Chapter 143, Scabies).
• Allergies to the dyes used in tattoos can occur. Although this is not strictly a CD because the dye is injected below the skin, the allergic process is similar (Figure 146-18).

• Identify and avoid the offending agent(s).4 SOR A
  • Be aware that some patients are actually allergic to topical steroids. This unfortunate situation can be diagnosed with patch testing.
  • In cases of nickel ACD, we recommend the patient cover the metal tab of their jeans with an iron-on patch or a few coats of clear nail polish.
• Cool compresses can soothe the symptoms of acute cases of CD.4 SOR C
• Calamine and colloidal oatmeal baths may help to dry and soothe acute, oozing lesions.3,4 SOR C
• Localized acute ACD lesions respond best with mid-potency to high-potency topical steroids such as 0.1% triamcinolone to 0.05% clobetasol, respectively.4 SOR A
• On areas of thinner skin (e.g., flexural surfaces, eyelids, face, anogenital region) lower-potency steroids such as desonide ointment can minimize the risk of skin atrophy.3,4 SOR B
• There is insufficient data to support the use of topical steroids for ICD, but because it is difficult to distinguish clinically between ACD and ICD, these agents are frequently tried. SOR C
• If ACD involves extensive skin areas (>20%), systemic steroid therapy is often required and offers relief within 12 to 24 hours. The recommended dose is 0.5 to 1 mg/kg daily for 5 to 7 days, and if the patient is comfortable at that time, the dose may be reduced by 50% for the next 5 to 7 days. The rate of reduction of steroid dosage depends on factors such as severity, duration of ACD, and how effectively the allergen can be avoided.4 SOR B
• Oral steroids should be tapered over 2 weeks because rapid discontinuance of steroids can result in rebound dermatitis. Severe poison ivy/oak is often treated with oral prednisone for 2 to 3 weeks. Avoid using a Medrol dose-pack, which has insufficient dosing and duration.4 SOR B
• The efficacy of topical immunomodulators (tacrolimus and pimecrolimus) in ACD or ICD has not been well established.4 However, one randomized controlled trial (RCT) did demonstrate that tacrolimus ointment is more effective than vehicle in treating chronically exposed, nickel-induced ACD.8 SOR B
• Although antihistamines are generally not effective for pruritus associated with ACD, they are commonly used. Sedation from more soporific antihistamines may offer some degree of palliation (diphenhydramine, hydroxyzine).4 SOR C
• Bacterial superinfection should be treated with an appropriate antibiotic that will cover Streptococcus pyogenes and S. aureus. Treat for MRSA if suspected.
• Once the diagnosis of any CD is established, emollients and moisturizers may help soothe irritated skin.4 SOR C

For ICD and occupational CD of the hands:

• Wear protective gloves when working with known allergens or potentially irritating substances such as solvents, soaps, and detergents.6,9 SOR A
• Use cotton liners under the gloves for both comfort and the absorption of sweat. Wearing cotton glove liners can prevent the development of an impaired skin barrier function caused by prolonged wearing of occlusive gloves.9 SOR B
  • There is insufficient evidence to promote the use of barrier creams to protect against contact with irritants.6,9 SOR A
  • After work, conditioning creams can improve skin condition in workers with damaged skin.9 SOR A
• Keep hands clean, dry, and well-moisturized whenever possible.
• Petrolatum applied twice a day is a great way to moisturize dry and cracked skin without exposing the patient to new irritants.

If the CD is severe enough (Figure 146-19), the patient may need to change work to completely avoid the offending irritant or antigen.

May need frequent follow-up if the offending substance is not found, the rash does not resolve and if patch testing will be needed.

Avoid the offending agent and take the medications as prescribed to relieve symptoms.

Patient Resources

• PubMed Health. Contact Dermatitis—http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001872/.
• The T.R.U.E. Test website has a wealth of information on reading labels, common allergens and patch testing for patients—http://www.truetest.com/.

Provider Resources

• American Family Physician. Diagnosis and Management of Contact Dermatitis—http://www.aafp.org/afp/2010/0801/p249.html.
• The T.R.U.E. Test website has a wealth of information on patch testing for healthcare professionals—http://www.truetest.com/.