Dermatology Online Journal

Dermoscopy of black-spot poison ivy
Ryan K Rader¹ BS, Ruipu Mu² BS, Honglan Shi² PhD, William V Stoecker¹ MS MD, Kristen A Hinton¹ BS
Dermatology Online Journal 18 (10): 8

1. Stoecker & Associates, LLC, Rolla, Missouri
2. Missouri University of Science and Technology, Department of Chemistry, Rolla, Missouri

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Abstract

Black-spot poison ivy is an uncommon presentation of poison ivy (Toxicodendron) allergic contact dermatitis. A 78-year-old sought evaluation of a black spot present on her right hand amid pruritic vesicles. The presentation of a black spot on the skin in a clinical context suggesting poison ivy is indicative of black-spot poison ivy. Dermoscopy revealed a jagged, centrally homogeneous, dark brown lesion with a red rim. A skin sample was obtained and compared against a poison ivy standard using ultra-fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS). This finding confirmed the presence of multiple urushiol congeners in the skin sample. Black-spot poison ivy may be added to the list of diagnoses that show a specific dermoscopic pattern.

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Introduction

Figure 1	Figure 2
Figure 1. Clinical black-spot urushiol image Figure 2. Contact, non-polarized image of black-spot urushiol

A 78-year-old female sought evaluation of pruritic vesicular lesions on the right hand and a 6mm irregular “black spot” in the same area that had arisen 5 days prior. Examination was consistent with “black-spot” poison ivy (Figures 1 and 2). Scraping with a Gillette^® blade easily removed the pigment without bleeding, confirming the superficial location of the pigment—within the stratum corneum. The scraped material was submitted for chemical analysis by ultra-fast liquid chromatography—tandem mass spectrometry.

Chemical analysis

Extraction procedure

To obtain a comparison standard, poison ivy vines were procured from a single tree in St. Charles, Missouri. A methanol extract of the vines was prepared by mixing small sections with 5 mL methanol for 4 hours at room temperature. Two grams of poison ivy extract were diluted 100-fold with methanol/water (50:50) mixture containing 1 mM ammonium acetate followed by ultra-fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS). The skin sample was extracted with 1 ml methanol by the same procedure and UFLC-MS/MS analyzed after dilution.

Instrumentation

To perform UFLC-MS/MS, a 4000Q TRAP mass spectrometer (AB SCIEX, Concord, ON, CA) with an electrospray ionization interface and a Shimadzu UFLC system consisted of a degasser (DGU-30A3), two pumps (LC-20 AD XR), an auto sampler (SIL-20AC XR) and a column oven (CTO-20A) were utilized.

UFLC separation/Mass Spectrometry detection

The chromatographic separation was performed on a P kinetex C-18 reversed-phase column (75 x 3.0 mm i.d. 2.6 μm particle size, Phenomenex, Torrance, CA, USA) at a flow rate of 0.25 mL/min. The UFLC mobile phase was composed of methanol and water, both containing 1 mM ammonium acetate. Mass spectrometry utilized negative electrospray ionization (ESI–) with Q1 scan mode. The ion source temperature was set at 410°C with an ion spray voltage of –4500 V.

Results

Chromatograms of poison ivy extract and skin scraping extract are shown in Figure 3. Urushiol is shown in Figure 4 as a catechol (six-membered aromatic ring with adjacent hydroxyl groups), with an R group representing the urushiol congeners–long, aliphatic 15-carbon or 17-carbon side chains.

Figure 3	Figure 4
Figure 3. Chromatograms of poison ivy extract and skin scraping sample extract Figure 4. Urushiol molecule. R represents one of the possible urushiol aliphatic side chains

There were a total of 7 urushiol congeners identified in the poison ivy and skin sample (Table 1). Four urushiol congeners, C₁₅ monoene, C₁₅ saturated, C₁₇ diene, and C₁₇ monoene, were identified in both poison ivy extract and skin scraping sample extract. C₁₇ tetraene and C₁₇ triene were only identified in plant extract, not in skin scraping sample; C₁₅ diene was only identified in skin scraping sample, not in the plant extract.

Discussion

Poison ivy contact dermatitis affects an estimated 25-40 million people every year in the United States who are exposed to the resin of the Toxicodendrons species [1]. An uncommon reaction to poison ivy is black-spot poison ivy, in which the urushiol sap is blackened via a dopa oxidase-mediated oxidation process in the presence of oxygen and moisture [2]. Indeed, black residue has been shown on areas of Toxicodendron plants that have been injured [3]. Black-spot poison ivy is postulated to be uncommon because a high concentration of urushiol and direct contact is needed [4]. Correct diagnosis of this phenomenon is important, because these lesions may be confused clinically with melanoma [5, 6]. Dermoscopic examination allows a definitive diagnosis.

Dermoscopy revealed a jagged, centrally homogeneous, dark brown lesion with a red rim. The jagged shape suggests an uneven diffusion pattern of the toxin within the strateum corneum. The combination of this irregular outline together with the observed color, centrally brown and peripherally red, has not been previous observed. We propose that this dermoscopic appearance is unique for black-spot poison ivy. The UFLC-MS/MS urushiol spectrum for the poison ivy extract sample and the skin scraping sample provides analytic confirmation that the lesion contains urushiol, confirming black-spot poison ivy. The presence of pruritic vesicular lesions, in conjunction with the black deposit, substantiates the diagnosis [4, 6].

References

1. Baer RL. Poison ivy dermatitis. Cutis 1990;46(1):34-6. [PubMed]

2. McNair JB, Rhus dermatitis from Rhus toxicodendron, radicans and diversiloba (poison ivy): Its pathology and chemotherapy. Chicago: University of Chicago Press, 1923.

3. Guin JD. The black spot test for recognizing poison ivy and related species. J Am Acad Dermatol 1980;2:332-3. [PubMed]

4. Mallory SB, Miller OF, Tylor WB. Toxicodendron radicans dermatitis with black lacquer deposit on the skin. J Am Acad Dermatol 1982; 6:363-8. [PubMed]

5. Paniagua CT, Bean AS. Black-spot poison ivy: A rare phenomenon. J Am Acad Nurse Pract 2011;23(6)275-7. [PubMed]

6. Kurlan JG, Lucky AW. Black spot poison ivy: A report of 5 cases and a review of the literature. J Am Acad Dermatol. 2001 Aug;45(2):246-9. [PubMed]

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