20 Toxicodendron Dermatitis (Poison Oak, Poison Ivy, Poison Sumac; Also Known as Rhus Dermatitis )
INTRODUCTION
Plants of the genus Toxicodendron are found throughout East Asia, North America, and South America. Five species common to North America cause more cases of allergic contact dermatitis than all other contact antigens combined. These species are known best by their common designations:
1. Poison ivy (two varieties).
2. Poison oak (two varieties).
3. Poison sumac.
When these plants are bruised or injured, they emit a sap called urushiol, which con- tains a mixture of highly allergenic, cross-reacting catechols. Contact with this sap in suf- ficient quantity can induce immune recognition (sensitizing dose), and with subsequent exposure (eliciting dose), a delayed hypersensitivity reaction will occur. Once allergic, an immunologically competent person will continue to react with any threshold reexposure to the offending antigen.
Some portion of the plant must be damaged for exposure to occur. Smoke from wood that contains part of a toxicodendron plant can contain enough antigen to cause severe exposure. The plant resin dries rapidly under fingernails and on skin, clothing, tools, and sporting equipment. It will retain antigenicity indefinitely unless removed. Toxicodendron dermatitis is important not only because of its frequency, but also because it serves as a model for understanding other types of allergic contact dermatitis.
CLINICAL APPLICATION QUESTIONS
A young mother seeks help for an uncooperative 5-year-old with a 7-day history of dermatitis of the right posterior thigh, right buttock, and right foot. Examination reveals patches of secondarily infected (impetiginized) dermatitis. Some areas are urticarial, while others are clearly vesicular. Excoriations are present, and the mother states that the eruption has gradually spread over several days. The vesicular eczematous areas and exco- riations lead you to suspect toxicodendron exposure.
1. What additional pertinent history should you obtain?
2. The history reveals that 2 days prior to onset the 5-year-old went fishing with the father down by the river. What physical features of the rash would offer additional support for the diagnosis?
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From: Current Clinical Practice: Dermatology Skills for Primary Care: An Illustrated Guide D.J. Trozak, D.J. Tennenhouse, and J.J. Russell © Humana Press, Totowa, NJ
3. What laboratory data are indicated in this case?
4. Should hyposensitization with urushiol extract be considered in this patient?
5. What is the appropriate treatment for this patient?
APPLICATION GUIDELINES
Specific HistoryOnset
Toxicodendron dermatitis occurs most often in teenagers and young adults after recre- ational outings, and in young and middle-aged adult patients following both occupational and recreational exposure. Forestry, utility maintenance, timber, landscape, and agricul- tural workers are among those most frequently affected. The symptoms typically start with erythema and pruritus about 48 hours after the exposure. Exquisitely sensitive victims may react in as little as 6 hours, whereas persons with low levels of sensitization or min- imal antigen exposure may take up to a week to react. Different body regions have varied reaction times and some sites may require several days to respond.
When new sites continue to develop late in an episode (7 to 10 days or more), it is nec- essary to look for continuing exposure from fomites such as contaminated clothing, tools, or sporting equipment.
Evolution of Disease Process
The duration and severity of an individual reaction will be determined by the patient’s level of sensitivity, the degree of exposure to the antigen, and the skin areas involved. In average cases, the rash and pruritus worsen for the first week. During this period, new areas of involvement may develop. These are caused by variations in skin reactivity and the uneven distribution of the antigen. Blister fluid from active lesions does not spread the dermatitis. An average episode lasts 14 to 18 days. Without treatment, severe episodes may last as long as 1 month.
Evolution of Skin Lesions
Early lesions consist of pruritic patches of erythema that evolve within a few hours into raised erythematous plaques. Within 12 hours some areas will progress to a coarse orange-peel appearance composed of tiny vesicles. If the reaction is severe, 1- to 5-mm vesicles will follow. As noted above, new areas of dermatitis may occur for at least a week while the initial lesions intensify.
Because of the marked itching, the blisters are usually excoriated and ruptured so that secondary infection is a common complication. The presence or absence of sec- ondary impetiginization should always be assessed when treating any acute contact dermatitis.
Extensive facial or genital involvement may be accompanied by massive local edema that interferes with vision or micturition, respectively. When extensive lesions are present in these locations, prompt systemic therapy should be considered.
As the reaction wanes, the pruritus diminishes, the plaques of erythema regress, the vesicles deflate, then the vesicles dry and desquamate. The duration and intensity can be dramatically altered by early treatment.
Provoking Factors
In addition to the obvious cause, there are several hidden sources for this type of acute contact reaction. Several related plant and plant products contain identical or related cross- reacting antigens. Persons who are sensitive to toxicodendrons will also react to mango rind, lacquer produced from the sap of the lacquer tree (Japanese, Burmese, and black varieties), cashew nut oil (found in the cashew shell), ink produced from the resin of the India marking nut tree, and the fruit of the ginkgo tree.
Self-Medication
Self-treatment with myriad OTC medications for poison oak and poison ivy is com- mon. Many of these proprietary products are themselves potent sensitizers and should not be applied to dermatitic skin. Products that should be avoided in particular are those that contain “caine” anesthetics and diphenhydramine. OTC steroid creams that contain 0.5 to 1.0% hydrocortisone are readily available but are not potent enough to alter the course of this reaction, and the cream base may be irritating enough to contribute to the problem.
Supplemental Review From General History None.
Dermatologic Physical Exam Primary Lesions
1. Linear patches of erythema (see Photo 24).
2. Linear plaques of erythema (see Photo 24).
3. Vesicles, from pinpoint to 5 mm (see Photo 25).
Secondary Lesions 1. Excoriations.
2. Crusting (see Photo 26).
3. Impetiginization (see Photo 26).
4. Scale, late in the course (see Photo 26).
Distribution
Microdistribution: None.
Macrodistribution: Exposed skin will be heavily involved, while covered areas are protected or minimally affected. Doubly covered skin areas are spared except in instances where the antigen is transferred from the hand to the anogenital region.
The palmar and plantar skin seldom reacts despite heavy exposure. Airborne exposure from burning toxicodendron leaves and stems frequently affects the face and neck (see Photo 27).
Configuration
1. Streaks and linear plaques of vesicles on an erythematous plaque are characteris- tic (see Photos 24,25).
2. Large irregular plaques are sometimes present due to spread from contaminated palms to other skin areas. Occasionally, recognizable handprints can be seen.
3. Confluent lesions are common with airborne exposure (see Photo 27).
Indicated Supporting Diagnostic Data
Toxicodendron dermatitis is a clinical diagnosis. Laboratory testing is not indicated except in rare instances as mentioned under Conditions That May Simulate Toxi- codendron Dermatitis section.
Therapy Prevention
Avoidance: Practitioners should become familiar with the species of toxicodendron found in their geographic area and instruct patients with handouts and photographs show- ing the appearance of the plant and the most likely exposure sites. With the exception of poison sumac, the saying “Leaves of three, let them be!” conveys the basic message. An excellent article by Guin et al. (see ref. 27) contains superb color photographs and com- prehensive information about the characteristics and regional distribution of each major species.
Barriers: Several effective barrier products are available OTC: Ivy Block® (EnviroDerm), Stocko Gard®(Stockhausen Inc.), Hollister Moisture Barrier®(Hollister Inc.), Hydropel® (C&M Pharmacal), Poison Oak-N-Ivy Armor® (Tec Labs) and Tecnu Poison Oak-N-Ivy Armor®(Tec Labs). When applied prior to exposure and according to the package instructions, up to 90% of a reaction can be prevented if exposure occurs.
Removal of the antigen: If exposure to an offending toxicodendron is recognized, immediate washing with mild soap and water may totally prevent the reaction. The anti- gen penetrates the epidermis rapidly and after 10 minutes some penetration may occur.
There is agreement that washing within the first hour of exposure will mitigate the sever- ity of the reaction, and any exposed person should cleanse thoroughly at the first oppor- tunity to limit transfer of the resin to other skin areas. Exposure to this type of contact antigen can occur indirectly from the fur of pets wandering through the brush or from camping equipment that has come in contact with the resin. This may be the surreptitious cause of unexplained or persistent cases. Pets should be shampooed; camping equipment should be washed with detergent.
Hyposensitization: Two extracts of urushiol are commercially available for the pur- pose of hyposensitization. Successful treatment will result in milder and shorter reactions;
however, the results are transient and do not afford complete prevention. This procedure should be undertaken only by a dermatologist or allergist familiar with the process.
Because of the limited results, subjects should be carefully chosen and should be fully aware of the limited results and potential side effects.
Topical Therapy
Proprietary lotions: An array of OTC products is available at any pharmacy. These contain different combinations of ingredients that relieve the itching, dry the exudate from the vesicles, and prevent secondary infection. They may, in fact, be modestly effective in
mild cases. As noted earlier, several products contain benzocaine and diphenhydramine, which are both highly sensitizing when applied to dermatitic skin. These products are not effective in cases of severe or widespread exposure except for the local drying and antimi- crobial effect. A prescription cream containing 5% doxepin HCl is an effective antipru- ritic, but caution must be taken to avoid systemic side effects and drug interactions.
Topical steroids: Despite some claims to the contrary, topical steroid creams are of considerable value provided they are used appropriately. These products are effective in mild to moderate cases applied to the sites of active dermatitis that are not overtly blis- tered. In some cases, they are sufficient as monotherapy. In more severe cases, they can be used in conjunction with systemic medication on the areas of acute erythema. Once an area is overtly blistered, these medications cannot penetrate and are ineffective. Potency should be a group IV steroid or stronger.
Antihistamines: An antihistamine may be occasionally useful in an agitated patient with intense itching. In adult patients, 25 to 50 mg hydroxyzine QID or 10 mg doxepin QID can be used. In children, hydroxyzine or cyproheptadine in appropriate dosage for weight or age is recommended.
Systemic steroids: Severe reactions can be incapacitating and result in time lost from work or vacation. If a reaction is progressing rapidly, and especially if there is extensive facial or genital involvement with edema, systemic steroids should be considered.
Treatment for adults should start with 30 to 40 mg prednisone STAT dose, then 30 to 40 mg in a single morning dose for the next 14 days. The prednisone can then be rapidly tapered over the ensuing week. This 3-week regimen will usually avoid late flare-ups.
Conditions That May Simulate Toxicodendron Dermatitis Delayed Contact Allergy to Other Plants
Many other plants, reaction including house plants, trees, and ornamental garden cov- ers, 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.
Phytophotodermatitis
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 usu- ally bullous rather than vesicular, and are accompanied by sting or pain rather than itch- ing. The acute lesions are usually replaced by dark pigmentation, which resolves very slowly.
Other Contact Allergens
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.
Herpes Zoster
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 toxicoden- dron dermatitis. When in doubt, a Tzanck smear or rapid immunofluorescence (RIF) test for herpesvirus will help distinguish between them.
Bedbug Bites
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 der- matitis.
ANSWERS TO CLINICAL APPLICATION QUESTIONS
History ReviewA young mother seeks help for an uncooperative 5-year-old with a 7-day history of dermatitis of the right posterior thigh, right buttock, and right foot. Examination reveals patches of secondarily infected (impetiginized) dermatitis. Some areas are urticarial, while others are clearly vesicular. Excoriations are present, and the mother states that the eruption has gradually spread over several days. The vesicular eczematous areas and exco- riations lead you to suspect toxicodendron exposure.
1. What additional pertinent history should you obtain?
Answer:
a. History of prior toxicodendron sensitivity or other history of allergic con- tact dermatitis.
b. History of possible toxicodendron exposure especially in the 48-hour period preceding the onset of symptoms.
c. History of self-treatment that may have modified or worsened the problems.
In the absence of toxicodendron exposure, obtain a history of any other plant expo- sure, gardening, or exposure to other cross-reacting products such as mango rind.
2. The history reveals that 2 days prior to onset, the 5-year-old went fishing with the father down by the river. What physical features of the rash would offer additional support for the diagnosis?
Answer: A configuration with streaks and linear plaques is characteristic of plant- acquired contact allergy. This configuration is particularly typical of toxicoden- dron dermatitis.
3. What laboratory data are indicated in this case?
Answer: In this case no laboratory data are indicated.
4. Should hyposensitization with urushiol extract be considered in this patient?
Answer: No. Urushiol hyposensitization should be reserved for cases of extreme sensitivity or individuals with repeated episodes. Even in these cases, the efficacy of hyposensitization is questionable.
5. What is the appropriate treatment for this patient?
Answer:
a. Instruct the parent as to how to recognize local toxicodendron species.
b. Instruct the parent or victim to use an effective barrier product before anticipated exposure.
c. Instruct the parent or victim regarding prompt antigen removal when expo- sure does occur.
d. Give a broad-spectrum antibiotic such as a first-generation cephalosporin if there is significant secondary infection.
e. Give a group IV topical steroid BID and as needed for itching to the active lesions.
f. Give a sedating antihistamine at least at bedtime for sleep.
g. The degree of involvement described here does not warrant the use of sys- temic steroids.
