Approach
Diagnosis is typically clinical. It should be considered for any acute dermatitis affecting the face and arms, particularly in the summer. A history of outdoor activity and the presence of vesicles and blisters support the diagnosis.
History
There may be a history of mild dermatitis following previous outdoor activities suggestive of prior exposure and sensitization.
The patient may be able to confirm exposure to one of the species by identifying the plant from a picture. American Academy of Dermatology: poison ivy, oak, and sumac Opens in new window US Department of Agriculture: PLANTS database (search for: toxicodendron) Opens in new window CDC National Institute for Occupational Safety and Health: plant identification Opens in new window Occupation may be important if outdoor work is common. If direct contact cannot be elicited, exposure to pets or livestock who may carry the antigen on their fur may be sufficient. Exposure to smoke from burning plants may cause breathing difficulties, as the antigen is heat-tolerant and can be carried by smoke. Chicken cooked with Toxicodendron species bark (rhus chicken) is a common traditional remedy in Korea. This can lead to a systemic contact dermatitis 4.0 ± 1.5 days after ingestion. Clinical features include generalized maculopapular eruptions, neutrophilia, and leukocytosis.[18]
Symptoms and timeframe
Patients generally complain of itchy or burning skin and develop redness, swelling, and blisters (vesicles and bullae) at the site of contact with the allergenic urushiols.
Symptoms usually start within 24 to 72 hours of exposure to the plant and may start as soon as 5 hours after exposure, typically with crusting, weeping, and oozing of the lesions. New lesions may continue to appear up to 15 days after exposure. The dermatitis usually settles in 7 to 15 days but may persist for 6 weeks.
Appearance
The dermatitis is usually clearly demarcated with sharp edges to the rash and linear distribution of blisters where the plant has brushed against the skin.[19] Palm prints of dermatitis may be seen if patients spread the dermatitis by self-contact. A generalized erythema may be seen if there has been extensive exposure. Other clinical presentations include erythema multiforme-like reactions, and exanthematous and urticarial eruptions. Stomatitis and anal itch have been described after chewing the plant leaves or secondary to hyposensitization treatments. [Figure caption and citation for the preceding image starts]: Phytodermatitis from contact with Toxicodendron succedaneum. Note the linear streaks from the plant having brushed against the forearmFrom the personal collection of Dr M. Rademaker; used with permission [Citation ends].
Black-spot poison ivy dermatitis consists of asymptomatic black lesions on the skin that cannot be washed off. These lesions become pruritic papules, but have been mistaken for melanoma.[20] It may have a specific dermoscopic appearance, namely a jagged, centrally homogeneous, dark brown pigmentation with a red rim. The jagged shape suggests an uneven diffusion pattern of the toxin within the stratum corneum.[21]
Distribution
The most commonly affected areas are the backs of hands, arms, lower legs, and face, but will depend on the activity and the clothing the individual wore at the time of contact. Genital involvement can occur through transfer from contaminated hands.
Investigations
Investigations are not usually required. Diagnosis is made clinically on history and examination findings. Samples of suspect plants can be collected and sent for identification at local garden centers and botany schools. Direct contact with the plants should be avoided by wearing vinyl gloves (as urushiols can penetrate rubber or latex) and keeping samples in sealed plastic bags. The black-spot test can also help identify the plant: three to four leaves of the suspect plant are placed in a folded sheet of white paper and crushed against a hard surface, sufficient to create a wet spot on the paper. If positive, this spot should begin to turn dark after 10 to 15 minutes and becomes black after 24 hours, due to oxidation of the urushiols into a lacquer.[2]
Assessing severity
There are no definitive criteria to define mild, moderate, and severe dermatitis, but broad classification helps direct initial therapy. This is usually a clinical judgment based on:
Symptoms of itch; some patients will complain significantly of itch with minimal signs, while others will tolerate extensive dermatitis. Very itchy rashes are more likely to become secondarily infected from excessive scratching and therefore may be treated as moderate to minimize this risk.
Extent of disease: from a small localized area on one limb (mild end of spectrum) to extensive disease involving >30% of body area (severe).
Severity of the dermatitis: mild erythema only (mild dermatitis) to large bullae formation (severe).
Duration of dermatitis: 1-2 days to 10-20 days (mild to severe).
Very itchy dermatitis with large bullae, covering wide areas, and present for >1 week may be treated as severe. Small localized patches of mildly itchy erythema of a couple of days' duration may be treated as mild. Moderate dermatitis may have features of either or both these extremes.
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