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