So you think you have Lyme Disease?
During a routine skin exam, I noticed an unusual black dot on my patient’s right forearm. He didn’t have many moles, so it was quite striking.
“How long has this been there?”
“It definitely wasn’t there yesterday morning,” he replied.
So I put my dermatoscope (basically a handheld magnifying glass with a light source) on the lesion and saw this:
So I said, “You have a tick on you…”
He was a bit stunned, as expected. On further questioning, he said he had a dog at home but never went into the woods or parks. Overall he felt fine — no joint pains, fevers, malaise. So what now?
First things being first, the tick needed to be removed. But you shouldn’t just take tweezers and pull them off, as that risks tearing the tick in half and leaving the mouth in, leaving the disease transmitting portion of the tick behind.
A simple, popular and effective approach involves two common household items: liquid soap and a q-tip. The technique is nicely demonstrated here:
We tried this approach and … success! The tick had been extracted en bloc, shown below:
It was too soon for him to have full blown Lyme disease. So the question was whether or not he should get prophylaxis. This would involve one dose (at 200 mg) of an antibiotic called doxycycline. Fortunately, the Infectious Diseases Society of America has some nice guidelines for us, and these guidelines are nicely tabulated on UpToDate:
So let’s walk through these.
1. Attached tick identified as an adult Ixodes scapularis tick (deer tick).
This is important because the Ixodes or blacklegged deer tick is the one that carries Lyme disease bacterium, Borrelia burgdorferi. A comparison of our tick and some look-alikes confirms that we are dealing with an adult Ixodes scapularis tick.
2. Tick is estimated to have been attached for at least 36 hours.
3. Prophylaxis is begun within 72 hours of tick removal.
There’s this tight window of the tick being attached for more than 36 hours or fewer than 72 hours for meeting prophylaxis guidelines. This is based on the observation that removal of the tick within 2–3 days of attachment usually prevents transmission of the disease causing bacterium (B. burgdorferi), and that Lyme disease is usually transmitted by allowing the tick to feed to repletion (~4–5 days).
According to our patient, he said the tick was not there yesterday morning, suggesting the tick could not have been attached for more than a day. So he would not meet criteria #2.
4. Local rate of infection of ticks with B. burgdorferi is at least 20 percent.
The exact rate of infection was rather hard to find. An incidence map for 2018 from the CDC shows there’s a lot of cases in Pennsylvania, so it probably’s reasonable to assume criteria #4 is met. As a side note, it’s interesting to see how the incidence of Lyme disease has risen in the past couple decades (see below).
5. Doxycycline is not contraindicated.
Our patient denied any allergies to doxycycline, was over the age of 8 and was neither pregnant nor lactating.
So everything rested on our patient’s word that he likely did not fall within the time window that the guidelines had suggested for optimal prophylaxis. So the textbook move would have been watchful waiting. And this idea is supported by the observations that 1) an overwhelming majority of patients with Lyme disease will develop a distinct rash called erythema migrans (perhaps to be discussed another time), 2) early therapy leads to excellent outcomes and 3) unnecessary antibiotic consumption leads to microbial resistance and mutation into superbugs.
But could it have been possible he just didn’t notice the tick yesterday because it was so small? Despite reading it hundreds of times in the textbook, something just felt unsettling about physically removing an Ixodes tick and not doing something active about it. We gave him the one dose of prophylactic doxycycline. This was probably not the best antibiotic stewardship (sorry to all the infectious disease doctors reading this), but what would you have done?
