Plant Contact Dermatitis

April 12, 2012

Poison ivy, oak, or sumac? What is this "itchy rash" that appeared 2 days after the patient cleared some "weeds" from the yard. What should be done about it?

A patient presented for help with an “itchy rash” on the arms of 2 days’ duration. The eruption appeared after she had helped her parents clear thick overgrowths of “weeds” from the yard.

Key point: Almost the entire rash was composed of linear arrays of papules and small blisters. Pruritic linear vesicles are virtually always caused by plant contact dermatitis. Poison ivy, oak, and sumac are the most common causes, and they vary in prevalence by geographic area.

Treatment: Mild cases of very limited extent can be treated with twice-daily or three-times-daily application of a potent topical corticosteroid. More extensive disease requires a 2- to 4-week, tapering course of oral corticosteroids (such as prednisone, starting at 40 to 60 mg/d).

Note: Sensitivity to the rhus family of plants is essentially lifelong and difficult to completely eliminate, even following desensitization protocols.