11.01 Rhus (Toxicodendron) Contact Dermatitis (Poison Ivy, Oak, or Sumac)

agk’s Library of Common Simple Emergencies

Presentation

The patient is troubled with a pruritic rash made up of tense vesiculo-papular lesions on a mildly erythematous base. Typically these are found in groups of linear streaks and may be weeping, crusted, or confluent. If involvement is severe, there may be marked edema, particularly on the face and periorbital and genital areas. The thick protective stratum corneum of the palms and the soles generally protect these areas. The patient is often not aware of having been in contact with poison ivy, oak, or sumac but may recall working in a field or garden from 24 to 48 hours before the onset of symptoms.

What to do:

• Have the patient apply cool compresses of Burow’s solution (Domeboro Powder Packets 2 packets in 1 pint of water) for 20- 30 minutes every 3-4 hours (more often if comforting).
• Small areas can be treated 2-3 times per day, enhanced at night with an occlusive plastic (Saran) wrap dressing.
• Diphenhydramine (available over the counter as Benadryl) or Hydroxyzine (Atarax) 25mg po q6h will help mild itching between application of compresses.
• Tepid tub baths with Aveeno colloidal oatmeal (one cup in 1/2 tub) or cornstarch and baking soda (1 cup of each in 1/2 tub) will provide soothing relief.
• When there is involvement of the face, in severe reactions or in situations where the patient’s livelihood is threatened, early and aggressive treatment with systemic corticosteroids should be initiated. Prednisone (60-80mg a day tapered over 2 weeks) will be necessary to prevent a late flare-up or rebound reaction. One 40mg dose ot intramuscular triamcinolone acetonide (Kenalog) will be equally effective.

What not to do:

• Do not try to substitute pre-packaged steroid regimens (Medrol Dosepak, Aristopak). The course is not long enough and may lead to a flare up.
• Do not allow patients to apply fluorinated corticosteroids such as Topsyn or Valisone indefinitely to the face, where they can produce premature aging of the skin.
• Do not institute systemic steroids in the face of secondary infections such as impetigo, cellulitis, or erysipelas. Also, do not start steroids if there is a history of tuberculosis, diabetes, herpes or severe hypertension.

Discussion

Poison oak and poison ivy are forms of allergic contact dermatitis that result from the exposure of sensitized individuals to allergen in sap. These allergens induce sensitization in more than 70 percent of the population, may be carried by pets, and are frequently transferred from hands to other areas of the body in the first few hours before the sap becomes fixed to the skin. The gradual appearance of the eruption over a period of several days is a reflection of the amount of antigen deposited on the skin and the reactivity of the site, not an indication of any further spread of the allergen. The vesicle fluid is a transudate, does not contain antigen, and will not spread the eruption elsewhere on the body or to other people. The allergic skin reaction usually runs a course of about 2 weeks which is not shortened by any of the above treatments. The aim of therapy is to reduce the severity of symptoms, not to shorten the course.

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