After working in garden, patient presents with raised lesions on forearm

What’s your diagnosis?

James H. Brien

A healthy, 19-year-old noticed some pruritic, somewhat raised erythematous lesions on her left forearm (Figure 1). The middle lesion had an unusual linear appearance.

Figure 1. Showing lesions on the left forearm. Image: James H. Brien, DO

Upon closer inspection, it appeared to have a “bumpy” component, but no vesicles or pustules were seen (Figure 2). She first noticed the lesions on a warm summer day, soon after finishing working in her family’s garden for a couple of hours, mostly pulling weeds, clearing vines and trimming rose bushes. She received a few mosquito bites but was unaware of any of other biting insects. The lesions are painless but do have some associated pruritis. Her exam is otherwise normal with no other complaints. Further history reveals that she has never had any other skin problems, and that no one else in the home has a history of similar lesions.

Figure 2. Closeup of one of the lesions in Figure 1. Image: James H. Brien, DO

What’s your diagnosis?

A. Contact dermatitis (poison ivy)
B. Cutaneous herpes simplex
C. Sporotrichosis
D. Southern tick-associated rash illness, or STARI

Answer and discussion:

The answer is contact dermatitis (A), caused by the Toxicodendron genus of plants that produce urushiol, an oily substance that can provoke an allergic reaction of the skin. There appear be multiple closely related species in different geographical locations that are generally referred to as poison ivy. This is a common cause of summertime skin rashes in those unlucky people who are “allergic” to the urushiol, which is contained in the plant’s leaves and stems. The urushiol can be transferred by direct contact with the plant, or by a contaminated artifact or pets. There appear to be varying degrees of sensitivity to these plants, from minimal to severe. The patient in this case had minimal involvement, whereas the patient shown in Figures 3 and 4 had severe involvement, aggravated by spread by his own hands to his face. The best management is avoidance of contact by keeping a lookout for the plant, which can usually be recognized by its characteristic three-leaf configuration, with the middle leaf having a longer stem (Figure 5). You can find numerous examples by simply searching poison ivy on the internet. The treatment is to not scratch the lesions and apply topical corticosteroids, except on the face. For severe cases, and those with facial involvement, oral steroids may be needed (see reference below). After topical triamcinolone for a few days, the patient’s lesions were significantly improved (Figure 6).

Figure 3. Severe contact dermatitis due to poison ivy on the face. Image: James H. Brien, DO

Figure 4. The same patient depicted in Figure 3, shown at a different angle. Image: James H. Brien, DO

Figure 5. Poison ivy plant with the characteristic three-leaf configuration. Note the longer stem of the middle leaf. Image: James H. Brien, DO

Figure 6. Close-up of lesion shown in Figures 1 and 2 after treatment. Image: James H. Brien, DO

One can certainly see cutaneous herpes simplex virus lesions displayed in a similar linear pattern (Figure 7), and they may look and feel similar to those caused by poison ivy. There can be significant inflammation as well. However, HSV lesions are more likely to display discrete vesicles with surrounding erythema, as shown. Additionally, there may be a history of similar lesions seen in the same location in the past. Also, a negative history of working in an area outdoors prior to the onset would make poison ivy highly unlikely.

Figure 7. Cutaneous herpes simplex virus lesions in a mixed, linear and clustering pattern. Image: James H. Brien, DO

Sporotrichosis is caused by invasion the fungus, Sporothrix schenckii complex, which establishes a chronic infection after contaminating an injury to the skin and lymphatic channels, with ulceration being typical (Figure 8). The diagnosis may require a tissue sample for microscopic analysis and/or culture. Currently, molecular techniques are not widely available, if at all. The recommended treatment is usually oral itraconazole (see the Red Book for dosing) for up to 6 months

Figure 8. A well-established case of cutaneous sporotrichosis, originally shown in the March 2011 column. Image: James H. Brien, DO

STARI is caused by an unknown agent that is spread by the Lone Star tick, leaving a cutaneous lesion very similar to Lyme disease (Figure 9). In fact, it is frequently misdiagnosed as Lyme disease (including by me). Diagnosis requires some suspicion in the geographic area where the transmitting ticks are found — typically, from the Eastern United States down to the Southeastern and South-Central states. Since there can be significant overlap of areas where one may also find Lyme disease, a description of the tick may be all that is needed, as the Amblyomma americanum (Lone Star tick) is much larger than Ixodes scapularis, the tick that carries the pathogen that causes Lyme disease (Borrelia burgdorferi), except in the Northwestern states where Ixodes pacificus is found.

Figure 9. STARI rash. Image: Jay Capra, MD

Columnist comments:

An excellent resource for a quick review of poison ivy is the book, Pediatric Dermatology, 4th edition, by Mancini and Krowchuk, published by the American Academy of Pediatrics. There are many other summertime hazards to children, including heat and heat-related injuries, such as being left in hot cars; biting insects that may spread disease; swimming pools; sunburns; physical trauma, like head injuries and broken bones; snake bites and more. A little counseling can go a long way, and it may save a life.

By the way, the case presented here was a hypothetical one. She was not a 19-year-old, but was my wife at a somewhat older age, not to be divulged. Over the last 54 years, she has provided me with many opportunities to photograph typical poison ivy rashes. She can now spot the typical three-leaf configuration and vine characteristics like a hawk. The pictures I have of children are not typical minor rashes, but usually severe reactions, like the patient in Figures 3 and 4. Severe rashes are all that I ever get referred. That being said, please keep in touch, and if you have a good case with a publishable picture that you want to see in this column, please let me know, and I will help you make it happen. In the meantime, stay safe.

References:

• American Academy of Pediatrics. Committee on Infectious Diseases. Red Book. 2021–2024 Report of the Committee on Infectious Diseases. American Academy of Pediatrics; 2024. https://redbook.solutions.aap.org/redbook.aspx. Accessed July 26, 2024.
• Mancini AJ, Krowchuk DP, eds. Pediatric Dermatology: A Quick Reference Guide. 4th ed. American Academy of Pediatrics; 2021.

For more information:

Brien is a member of the Healio Pediatrics Peer Perspective Board and an adjunct professor of pediatric infectious diseases at McLane Children's Hospital, Baylor Scott & White Health, in Temple, Texas. He can be reached at jhbrien@aol.com.