A problem with timing
I had the man repeat his story. It did not offer me any new directions. I considered the possibilities. Lyme disease famously caused a bulging eye rash with a central clearing, but the timing was all wrong. The ree-tick vector must be attached to the body for at least 36 hours to transmit its Lyme spirochete gift. And then it takes several days for the rash to appear. Could this world be caused by a toxin injected by a bite or sting? The time course seemed to be off as well. Insect bites usually cause an immediate reaction. A brown spotted spider can cause a slow reaction, but if it is serious, it causes skin blisters and necrosis – not this lumpy red rash. And how could it appear on the other leg? Did that mean that all it was was his bloodstream invaded and scattered throughout his body? Should we start the patient on doxycycline – the antibiotic used to treat most infections caused by tick bites? But the patient did not feel sick. He was just worried about the outcome. And so was I.
Keith Choate, a dermatologist, teaches residents at my clinic. This was one of his learning days. Raman and I found the dermatologist followed by a handful of residents. He was not with a patient, and so we described ourselves briefly. We brought Choate into the patient’s room. The occupants looked out the door. Choate introduced himself to the man, looked quickly at the twins and asked only one question.
One simple question
“Do you use triple antibiotic ointment?” he asked the patient. Triple antibiotic ointment is a mixture of three topical antibiotics: neomycin, polymyxin B and bacitracin. It is sold under the brand name Neosporin, but generic versions of the mixture are available and sold under the name Triple Antibiotic Ointment. The patient had used this ointment, he told Choate. But only a few times, because it did not help. “Well, do not use it again,” Choate advised. The rash was not an infection, helped by the topical antibiotic, but an allergy caused by it. This ointment is one of the most common causes of what is known as allergic contact dermatitis (ACD).
The skin contains a wealth of white blood cells that help protect the body against invaders that want to enter through it, the body’s largest organ. In allergic contact dermatitis, a benign substance that is in contact with the skin becomes mistaken as a predator, eliciting a protective inflammatory response. Some substances – including neomycin and bacitracin, two of the three antibiotics contained in this ointment – have been found to be common causes of this type of adverse protective reaction. According to one large study of surgical patients, more than 4 percent of the people who were exposed to ingredients found in triple antibiotic ointment developed allergic contact dermatitis. It is often listed among the top 10 causes of ACD, along with some of the common ingredients in lotions and fragrances.
Choate recommended a strong steroid cream to achieve the inflammation and rapid resolution of the rash. But it will take time to clean up, the dermatologist warned.
Make contact
As we left the room, Raman asked Choate how the rash spread to the other leg. His answer was simple and had a clue as to how he invented it. It’s a contact dermatitis, he reminded her. When the man crossed his ankles or put his legs next to each other, perhaps while he was sleeping, the ointment on one leg was brought into contact with the other.
I consulted the patient a week after he started the steroid cream. The rash disappeared, but slowly. He headed out to the spot in the garden where he felt the sting and searched the surrounding shrubs and grasses for clues as to what got him. He found no probable culprit. No mounds like beehives. No sparse plants like grass. No spider webs. It’s a mystery, he told me. But from now on, he averred, he will cut the lawn with long pants as well as socks and shoes.
