First, an exacting review of the anatomy of I. scapularis...
|This depiction is actually more realistic than how some CT politicians view ticks and Lyme disease.|
#1 The "bulls-eye" rash, while classic, is uncommon.
Anytime a sign is described as classic, you ought to expect that, basically, you will never see it. My rule of thumb when being pimped about how often you see a "classic sign" is to reply "Well, recent research, ah, I believe, shows a lower rate in the modern era, ah, about 15% I believe."
And the literature on erythema migrans (EM) backs me up. A "bulls-eye" pattern, with central-clearing, may have been more common years ago, when Lyme took weeks to diagnose. In contrast, a study from 2002 found that only 9% of confirmed EM had central clearing. Instead, the majority either were homogenous, or were darker centrally!
In fact, central clearing occurred at the same rate as rashes which had vesicles or a blue center.
So, all these are erythema migrans:
|Central vesicles (source)|
|Central raised punctum (source)|
|Triangular, rather than round (source)|
What should you look for, if not a bull's eye? Five key elements are:
- Blanchable erythema,
- Flat, with non-raised border.
- Large, and rapidly expanding (20 cm2/day).
#2 Don't routinely get "Lyme tests."
The patient lives in suburban Connecticut, it's July, they describe "flu-like" aching and chills, and you find a 15 cm diameter homogenously erythematous rash on their back. You're done - 2 weeks doxy 100 BID, and go see the next patient!
But what about a test, "just to make sure?" Hey, we're always getting tests. We order BNPs on patients who are on BiPAP and getting 400 µg/minute of nitro, we get a troponin on the patient being rushed to the cath lab for anterior "tombstones," we get a white count in, well, everyone. So why not order a test for Lyme?
Because they don't work well. Some of the pitfalls are:
- In early localized disease (i.e. EM) about 50% of patients will not yet have a rise in IgM levels.
- About 5% of the population can have a positive ELISA test at any given time.
- In the absence of a supportive history or clinical signs, a positive IgG just indicates past exposure.
- Elevated IgG, and even IgM, levels can be seen for a long time after successful treatment.
|And I enjoy trying to page PMDs almost as much as I enjoy this new yogurt flavor!|
#3 Lyme carditis
An otherwise healthy 35 y.o. male comes to the ED with severe presyncope, after having been found to have a heart rate of 30 in the walk-in clinic. He admits to having been told by a coworker at his landscaping job that he had a big red rash on his back 3 months ago (in July), but he never saw it himself. The blood pressure is 80/40, and the ECG shows a complete heart block with a narrow QRS.
How bad is this? I mean, complete heart block - yikes. What should we do right now? Does he need a permanent pacemaker? Will the echo show a nasty cardiomyopathy? How bad is the mortality?
Ok, in order:
- Not that bad. These blocks usually last under a week, once antibiotics have been started.
- Not a question... But AV blocks are very common in Lyme carditis - about 50% of patients.
- Put on pacer pads, order some ceftriaxone, and don't let him walk to the bathroom!
- Unlikely. Permanent conduction defects are rare, even though some folks need temporary pacing.
- Maybe in the short-term there can be some "reduced squeeze," but the long-term prognosis is very good.
- Almost unheard of: a recent review only found two case reports that plausibly link a death due to Lyme disease
#4 Prophylactic Doxycyline
If a deer tick has been for at least 36 hours, and the patient can take antibiotics within 72 hours after tick removal, and we're in Connecticut (i.e. a Lyme endemic area), the the patient should get doxycyline 200mg PO once.
There are a few wrinkles in this, however. For example, you can't do this for kids - there is no data for prophylactic-dose amoxicillin.
But most importantly, you have to know the risk-benefit numbers. First, what is the risk of developing erythema migrans after a tick bite, and how much does doxy help? The key NEJM study found:
It looks like most deer tick bites, even in Westchester, NY (a Lyme endemic area), do not result in EM. The risk tops out at about 10% for a somewhat engorged nymph, and plummet for the other categories. The one-time dose of doxy drops that rate down to a little over 1%. That's a pretty decent benefit.
Well, how about the risks of prophylactic dosing?
A 6% risk of vomiting, and 7% abdminal pain? Hmm.
So, another way of looking at it, the patient potentially has a 90% chance of having nothing happen (if no prophylactic dose), versus a 6% chance of being sick as a dog from the doxy. That's the choice!
The Bottom Line
There's a big fear about Lyme disease in Connecticut, and plenty of people work hard every day to make sure that the paranoia doesn't die down.
|Like one of our senators, who investigated and sued the Infectious Disease Society of America|
(spending at lot of CT tax money in the process), and was ultimately 100% in the wrong. ***
*** My own political views are not represented here, just a medical perspective. So, in order to balance out my criticisms of a Democrat, let me point out that no political party has a lock on pandering to the "chronic Lyme" folks. To highlight a recent example:
|He planned to "improve synergy" in treating Lyme. Cool.|