Rhus Dermatitis

Rhus Dermatitis (Poison Ivy, Poison Oak, Poison Sumac)

Description :

■ Poison ivy, poison oak, and poison sumac (plants of the Anacardiaceae family) and Toxicodendron species are the most common causes of allergic contact dermatitis in the United States; this problematic prototype of contact dermatitis is rarely reported in Europe, although related plants grow in Southeast Asia, Central America, and South America.
■ Oleoresin (lipid-soluble portion) contains a mixture of highly allergenic catechol chemicals called urushiols, a term derived from the Japanese word for sap, urushi.

History :

■ Contact with the plant’s leaf, stem, or root, even in autumn and winter, results in a pruritic bullous eruption within 8 to 72 hours of exposure in a previously sensitized individual and within 12 to 21 days in an individual who has not yet been sensitized (primary sensitization).
■ Primary sensitization can result from exposure to the allergenic plant. This process requires an intact immune system. After an individual has become allergic (sensitized), repeat exposure will cause the rash to occur more promptly (a process called elicitation).
■ About half of American adults develop the rash if they are exposed; 30% to 40% require prolonged exposure to produce the dermatitis.
■ About 10% to 15% of Americans do not become sensitized (allergic).

Skin Findings :

■ Clinical findings vary with the quantity of oleoresin that contacts the skin, the pattern of contact, individual susceptibility, and regional variations in skin reactivity.
■ Findings include pruritic, edematous, linear erythematous streaks, usually with vesicles and large bullae on exposed skin.
■ Airborne particulate matter from burning the plant can result in intense, pruritic facial erythema and marked edema; the eyelids can be dramatically swollen.

■ Trauma to the skin from the plant may leave a temporary black mark on the skin—a clue to exposure and a result of dried and oxidized urushiol allergen.

Course and Prognosis :

■ The itchy eruption lasts from 10 days to as long as 3 weeks.
■ Short courses of oral corticosteroids (e.g., dose packs) are inadequate and may result in a rebound phenomenon with prompt blistering when discontinued.
■ The rash resolves completely without scarring.
■ Impetigo or cellulitis may occur from scratching and secondary bacterial infection (usually S. aureus).
■ Short-term disability and time lost from work are significant occupational problems associated with this contact dermatitis, especially among firefighters, foresters, landscapers, and outdoor workers.

Discussion :

■ Poison ivy is not spread by blister fluid and is not spread from person to person.
■ The allergenic oleoresin can be spread by contaminated clothing, garden tools, or animals.
■ Cross-reacting allergens from other plants of the Anacardiaceae family include mango peel, the oil of raw cashew nut shells, Japanese lacquer, and ginkgo fruit pulp. Individuals sensitized to poison ivy may also react after exposure to these related plants.
■ Poison ivy grows as a shrub or climbing vine. In the United States, Eastern poison oak is typically found in the Southeast, whereas Western poison oak grows typically on the West Coast, in the form of a small shrub or tree. Poison sumac prefers a moist location and is common in peat bogs and wetlands of the eastern United States and southeastern Canada.

Management :

■ The skin should be washed with soap to inactivate and remove allergic oleoresin, thereby preventing further skin penetration and contamination. Washing is most effective if done within 15 minutes of exposure.
■ Exposed clothing and tools should be cleansed with soapy water.
■ Short, cool tub baths, with or without colloidal oatmeal (Aveeno), are soothing for itching and swelling.
■ Calamine lotion controls itching, but prolonged use can lead to excessive drying.
■ Oral antihistamines (hydroxyzine and diphenhydramine) may control itching. They are sedating and may be best used at night to reduce nighttime scratching and promote rest, thus offering relief from the  
stress of intense itch, which often interferes with sleep.
■ Cool, wet dressings made with tap water or Burow’s solution are highly effective during the acute blistering stage. They are applied for 15 to 30 minutes several times a day for 1 to 4 days until blistering and severe itching are controlled. Cool, wet tap-water dressings are very useful for severe facial or eyelid edema.
■ A medium-potency topical steroid (groups II–V) should be generously applied after the wet dressing. If the periorbital skin is involved, a weaker topical steroid (groups VI–VII) is advised for a specified limited duration (twice daily for 7 days).
■ The immunomodulatory topical therapies, pimecrolimus (Elidel) and tacrolimus (Protopic), are not advised for acute allergic contact dermatitis to poison ivy, given their cost, the amount often required, and delay of efficacy compared with topical steroids.
■ A course of oral corticosteroids for severe, widespread inflammation is started at 0.5 to 1 mg/kg/day and is slowly tapered over 3 weeks.
■ A barrier cream, IvyBlock, contains quaternium-18 bentonite that can be successful in preventing the dermatitis or reducing the severity of reactions. However, it is essential that it be applied at least 15 minutes before anticipated exposure.
■ Poison ivy oleoresin in capsules and an injectable form for hyposensitization have been removed from the market as a result of side effects and incomplete efficacy. There are no means available currently for desensitization to poison ivy.

Pearls :

■ The classic presentation of poisonous plant contact dermatitis is variably sized vesicles and bullae appearing in a linear distribution on exposed skin.
■ Generally, repeated exposure over short periods of time (i.e., the summer months) results in increasingly severe bouts of the dermatitis.
■ Oral ingestion of raw or incompletely roasted cashews can cause an internal–external reaction—a sudden erythematous pruritic dermatitis in a characteristic distribution on the buttocks, upper inner thighs, and axillary vault in individuals sensitized to urushiol.

■ Poison ivy, poison oak, or poison sumac can involve wide areas. The decision to use oral or topical steroids depends on the severity of the symptoms, age of the patient, and potential for short-term adverse reactions anticipated through review of the medical history.
■ Short courses of low-dose systemic corticosteroids are inadequate treatment for severe, generalized cases of poison ivy.