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Contact%20dermatitis Diagnosis
Diagnosis
Allergic Contact Dermatitis
- An immunologic cell-mediated skin reaction to exposure of antigenic substances; patch test-positive
- Can be suspected in patients with both generalized and anatomically localized skin eruptions (eg hands, face, eyelids) that had contact with exogenous substances
Irritant Contact Dermatitis
- A nonimmunologic skin reaction to skin irritants; patch test-negative
- Results from innate immunity activation without prior sensitization
- Pathophysiological changes that may occur are disruption to the skin barrier, epidermal cellular changes and release of cytokine into the circulation
- In some situations, there is a simultaneous exposure to both an irritant and contact allergen or 2 contact allergens that can reduce the clinical threshold concentration to elicit response to a given allergen
Differentiating between Allergic Contact Dermatitis and Irritant Contact Dermatitis:
| Allergic Contact Dermatitis | Irritant Contact Dermatitis | |
| Risk group | Genetically predisposed | Everyone |
| Mechanism of response | Immunological response: Delayed hypersensitivity reactions | Nonimmunologic: Physical and chemical alteration of the skin epidermis |
| Nature of exposure | Can be very low concentration of low molecular weight hapten (eg metals, formalin, epoxy) after one or many exposures | Normally high concentration of organic solvent or soaps, etc after few to many exposures |
| Onset | Usually hours to days | Usually minutes to hours |
| Distribution | May correspond exactly to contactant (eg elastic waist band, wristband) | Indistinct borders |
| Diagnostic test | Based on patch test or usage test | Based on trial of avoidance or negative patch test |
| Management | Complete avoidance | Protection and reduced incidence of exposure |
History
Determine trigger factors based on:
- Medical history
- Physical exam
- Questioning on the relationship between skin condition and include:
- Date of onset
- Occupation
- Skin care products
- Exposure to light
- Histopathological examination of the skin biopsy may be done in atypical cases
Screening
Patch Testing
- Gold standard test in a patient wherein allergic contact dermatitis is suspected
- Involves reproducing under patch tests of an allergic contact dermatitis in an individual sensitized to a particular antigen
- Recommended in cases where symptoms persist despite avoidance of trigger factors and topical therapy
- Studies have shown that it is valuable to have the test done by a specialist in contact dermatitis with a clinic with access to extended series of allergens for the investigation of dermatitis in specific anatomical sites, occupational groups and chemical exposures
- Sensitivity of this test is 70% and specificity is 80%
- Specialty trays are helpful in conducting extensive patch testing for evaluation of occupational sources of dermatitis
- May consider using supplemental series of allergens depending on patient's exposure history
- Photopatch testing is indicated in photoallergic contact dermatitis
- Not recommended as a diagnostic test for irritant contact dermatitis
