Medical Mystery of the Week

       You are asked to make a diagnosis in this patient merely by looking at photos of her skin rash.
DIAGNOSIS: Poison ivy.
      Poison ivy, poison oak, and poison sumac are the most common causes of clinically diagnosed allergic contact dermatitis in North America, with approximately 50-75% of the US adult population being sensitive to these allergens.
      Whenever possible, sensitized individuals should avoid contact with the plant resins. Burning of these plants can result in resin inhalation and upper and/or lower airway allergic responses.
      Exposed individuals should immediately wash their skin with a detergent soap. Depending on its severity, treatments include calamine lotion and topical and/or systemic steroids. Desensitization regimens are not available, although persons repeately exposed to the resin may eventually become desensitized.

     The clinical clues to the diagnosis in this patient include the linear vesicles on an erythematous base (left picture) and the black patches on erythematous bases (right image). The principle allergen in poison ivy is urushiol, a resin that oxidizes on exposure to air changing from clear to black. The rash will not improve until the urushiol is washed off the skin.