Sunday, July 21, 2013

Lime's Disease - some underappreciated elements.

This is not meant to be a comprehensive review of B. burgdorferi, the life cycle of I. scapularis, or all the other stuff that belong in a thorough introduction to Lime's disease. Instead, I just want to highlight a few aspects that seem to have been under-appreciated.

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.
If the rash is equivocal-looking, you can get active and convalescent assays, but this is not routine, and should require discussion with the PMD.

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:
  1. Not that bad. These blocks usually last under a week, once antibiotics have been started.
  2. Not a question... But AV blocks are very common in Lyme carditis - about 50% of patients.
  3. Put on pacer pads, order some ceftriaxone, and don't let him walk to the bathroom!
  4. Unlikely. Permanent conduction defects are rare, even though some folks need temporary pacing.
  5. Maybe in the short-term there can be some "reduced squeeze," but the long-term prognosis is very good.
  6. Almost unheard of: a recent review only found two case reports that plausibly link a death due to Lyme disease
Lastly, atropine is not felt to do much, good or bad.

#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. ***
So, as an emergency doctor in this wacky state, you should know this disease pretty well, so you can identify and treat "Lime's disease" appropriately. You can download the excellent IDSA guidelines for definitive information, or check out the CDC website for clinicians as well.

***  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.