Delayed Contact Allergy to Other Plants
Many other plants, reaction including house plants, trees, and ornamental garden covers, can cause a delayed hypersensitivity. Depending on the plant and mode of contact, the pattern may show streaks of acute vesicular eczema indistinguishable from toxicodendron dermatitis. The source must be sought from the history and confirmed with a patch test.
Certain wild plants, some varieties of meadow grass, and some common garden plants contain a photosensitizing furocoumarin in their sap that, if deposited on the skin and exposed to sun or long-wave ultraviolet light, will produce an accelerated sunburn reaction. The pattern is often one of prominent linear streaks. These reactions are usually bullous rather than vesicular, and are accompanied by sting or pain rather than itching. The acute lesions are usually replaced by dark pigmentation, which resolves very slowly.
When toxicodendron dermatitis shows a patchy rather than linear pattern, it must be distinguished from other causes of delayed hypersensitivity. Careful historical data and indicated patch testing for suspect substances will need to be carried out if the problem persists. Dermatologists are specifically trained in this area.
Peculiar as it may seem, early acute zoster can be very similar to early toxicodendron dermatitis. Both eruptions can show a linear "dermatomal" pattern. Zoster with minimal acute neuritis may be pruritic rather than painful. Early toxicodendron dermatitis may exhibit only modest itching. Both conditions may have an orange-peel surface and similar-sized vesicles (see Photo 28). History of recreational exposure helps. Dysesthesia rather than itching, unilateral distribution, and umbilication of the vesicles suggest zoster. Intense pruritus, widespread satellites, and extension over the midline favors toxicodendron dermatitis. When in doubt, a Tzanck smear or rapid immunofluorescence (RIF) test for herpesvirus will help distinguish between them.
The bedbug (C. lenticularis) can cause linear, vesicular bite patterns in a sensitized victim. Hemorrhagic puncta from the bite helps to distinguish it from toxicodendron dermatitis.
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