A previously healthy 11-year-old girl presented with an intensely pruritic widespread eruption. The patient reported that this had been ongoing for two days. It initially started with itching and redness of the inner thighs and spread to involve the entire face as well as the arms, neck, and abdomen. She notably developed black spots on her arms as well. Physical examination revealed erythematous eczematous papules and plaques on the neck, arms, legs, and abdomen. Diffuse erythema and swelling of the face was noted (Fig. 1). In addition, there were scattered erythematous papules with central black discolored macules on her arms (Fig. 2). The black material could not be removed with saline gauze or isopropyl alcohol. No other skin lesions of concern were identified in the areas examined. A diagnosis of black spot poison ivy (Toxicodendron dermatitis) was made.
Poison ivy is characterized by a generalized, pruritic, erythematous rash with vesicles and papules in a linear distribution. Black spot poison ivy presents in a similar fashion, with the addition of black lacquer-like macules with surrounding erythema. Our patient presented with these classic erythematous papules and plaques studded with black shiny spots. Histology of these lesions reveals yellow material in the stratum corneum with epidermal necrosis, in addition to classic features of acute allergic contact dermatitis.
When Toxicodendron plants are injured and their sap is exposed to air, oleoresin turns “coal-black.” Contact with a sufficient concentration of this oleoresin will produce black spot poison ivy. The resultant black spots are quite evident; thus, diagnosis can generally be made clinically. If there is doubt, diagnosis can be aided by pathology.
Treatment of black spot poison ivy, like poison ivy, involves oral and topical steroids, combined with antihistamines if the patient continues to experience pruritus.[4, 5] Typically, the rash resolves within 1–3 weeks, and patients do not require further monitoring. We treated our patient with a 20-day prednisone taper, topical clobetasol, and hydroxyzine. She responded well to treatment and did not require further follow-up.
Although a rare phenomenon, black spot poison ivy remains an important diagnosis to consider in evaluating a patient with a pruritic, erythematous rash studded with glossy black macules. An accurate diagnosis can alleviate patient fears about pigmented or necrotic lesions and can allow for prompt treatment. An accurate diagnosis can also allow for proper patient counseling to prevent future re-exposure.