Hi, I’m Bobbi Pritt, Director of the Clinical Parasitology Laboratory and vice-chair of
education for the Department of Laboratory Medicine and Pathology at Mayo Clinic.
You probably know that you can get Lyme Disease from a tick bite, but not all ticks carry
the disease.
In this month’s “Hot Topic” my colleague, Dr. Elli Theel, will discuss diagnostic testing
options for patients with suspected neuroinvasive Lyme disease or Lyme neuroborreliosis.
I hope you enjoy this month's Hot Topic and I want to personally thank you for allowing
Mayo Clinic to be a partner in your patients' health care.
Thank you for the introduction and also to the viewers for joining us today.
Before we begin, just a note that I do not have any relevant financial disclosures to
share.As you view the presentation, consider the following important points regarding testing,
including, “How is this testing going to be used in your practice?
When should the tests be used?
And, how will the results impact patient management?”
Ok, for today’s “Hot Topic,” I’ll be discussing diagnostic testing options for
patients with suspected neuroinvasive Lyme disease or Lyme neuroborreliosis.
And to start, as a reminder, Lyme disease is caused by an infection with any of the
pathogenic members of the Borrelia burgdorferi sensu lato complex, of which there are more
than 15 species, although only about 7 have been associated with human disease, among
which B. burgdorferi sensu stricto, is the most common agent causing Lyme disease in
North America.
Importantly, all of these agents are transmitted through the Ixodes species of ticks, and in
2016, more than 36,000 cases of Lyme disease were reported to the Centers for Disease Control
and Prevention (CDC) in the United States.
Notably, though, this is actually considered a vast underrepresentation of the true number
of infections that occur each year, which is likely closer to 300,000 to 400,000 cases
annually.
Lyme disease can progress through multiple disease stages, with neuroinvasive disease
occurring in up to 15% of untreated patients.
Neuroinvasive disease can present in a variety of different ways, and while a detailed discussion
of these manifestations is beyond the scope of this presentation, the most common clinical
features are meningoradiculitis, lymphocytic meningitis, and cranial nerve palsy, which
typically present 4 to 6 weeks post infection, although a wider range from 1 to 12 weeks
has been reported in the literature.
Despite these common features, however, they remain nonspecific, and this is acknowledged
by the current Lyme disease guidelines from the Infectious Diseases Society of America
(IDSA), which states that the “neurologic manifestations are too nonspecific to warrant
a purely clinical diagnosis of Lyme neuroborreliosis” and that “laboratory support for the diagnosis
is required.”
In patients with symptoms suggestive of Lyme neuroborreliosis, a number of factors should
be considered before proceeding directly to testing for this infection.
First and foremost, the risk of infection should be considered, including specifically
whether the patient has had recent exposure to ticks in a Lyme disease-endemic region.
Also, the time of year that the patient presents is important, keeping in mind the lack of
tick activity in late winter months.
Patients with neuroinvasive Lyme disease typically have CSF pleocytosis with a lymphocytic predominance,
alongside mildly elevated protein levels.
Notably, glucose levels are typically normal in these patients.
Finally, providers have increasingly questioned whether testing for CXCL13, a B-cell attractive
chemokine is useful as a marker in patients with suspected neuroinvasive Lyme disease.
Testing for this analyte is not currently recommended because although it is elevated
in patients with Lyme neuroborreliosis, it is also elevated in patients with other non-Lyme
disease neuroinflammatory conditions and therefore does not offer sufficient discriminatory power
for diagnosis of neuroinvasive Lyme disease.
So, for patients with compatible symptoms and exposure history, what testing is available
for diagnosis of Lyme neuroborreliosis?
Well, the Borrelia spirochete can be cultured, however, the sensitivity of culture from CSF
in patients with neuroinvasive Lyme disease is less than 10%.
Additionally, culture is no longer routinely performed or offered in hospital or reference
laboratories, which alongside the low sensitivity of this method in general, excludes culture
as a routine means of diagnosis.
Molecular testing through RT-PCR for detection of DNA from Lyme Borrelia is an alternative
option.
Notably, however, there are no FDA-approved PCR assays for Lyme disease, and all of the
currently available molecular tests are laboratory developed and may differ in their performance
characteristics.
Additionally, the sensitivity of PCR testing for Lyme Borrelia varies.
This table summarizes the sensitivity of different PCRs for B. burgdorferi from multiple different
studies performed on various specimen sources, and you’ll note that while sensitivity is
comparatively high in synovial fluid and erythema migrans tissue biopsies, ranging from 68 to
78%, sensitivity is quite low in CSF, with a median sensitivity of 22.5%.
And the reason for this low sensitivity is largely due to the very low bacterial burden
in the central nervous system.
So, PCR is also not the best choice for detection of this neuroinvasive infection, leaving us
with serology as the preferred diagnostic method for neuroinvasive Lyme disease.
As a reminder, diagnostic testing for disseminated Lyme disease is currently performed in accordance
with the standard two-tiered testing algorithm, which starts with either an ELISA or IFA screen
for detection of total antibodies to B. burgdorferi.
If the screen is negative, this should prompt the provider to consider an alternative diagnosis,
or if the patient presents early following exposure, the provider should collect and
test a convalescent sample.
On the other hand, if the screening assay is positive or equivocal, then a second test
is required, using a western or immunoblot to detect specific IgM and/or IgG-class antibodies
to B. burgdorferi, depending on the duration of symptoms.
For the IgM blot to be considered positive, we need to see the presence of specific antibodies
to at least two out of a possible three Borrelia antigens on the blot, and for a patient to
be considered positive for IgG antibodies, we need to see reactivity to at least five
out of a possible ten antigens on the blot.
There are a number of limitations associated with testing for antibodies to B. burgdorferi
in only serum from patients with suspected neuroinvasive Lyme disease.
First, up to 15% of patients with Lyme neuroborreliosis may be seronegative for antibodies to B. burgdorferi
in serum, which may lead to the inappropriate exclusion of neuroinvasive disease in a patient
that is truly infected.
Also, there is approximately a 5% background seropositivity rate for antibodies to B. burgdorferi
among individuals living in Lyme-endemic regions, which could possibly lead providers to strongly
consider neuroinvasive disease in patients without the infection.
Further testing of these patients would be necessary to confirm CNS infection.
Use of the two-tiered testing algorithm is also not recommended to be performed on CSF
for a number of reasons.
First, this algorithm was developed for evaluation of antibodies detected in serum, not those
that may be synthesized in the CNS.
And second, it is important to differentiate whether antibodies detected in the CSF are
there due to intrathecal antibody synthesis, whereby B-cells are recruited into the CNS
and produce antibodies, or whether these antibodies are present in the CSF due to passive transfer
across a compromised blood-CSF barrier due to injury or inflammation.
To help differentiate between these two scenarios, a Lyme antibody index (AI) can be performed.
The antibody index is essentially a ratio of anti-Borrelia-specific antibodies in CSF
to serum, which are normalized to total IgG in both specimen sources, which are ideally
collected concurrently, and it corrects for blood-CSF permeability and/or abnormally elevated
intrathecal antibody synthesis.
The equation on the right is a simple, generic equation of this ratio to help you visualize
it, however, in reality, there is a lot more math
that goes into determining an AI and those equations are shown in this table.
I won’t go into the details of this today, however, they take into account normal CSF
turnover and diffusion rates, among other factors.
Ultimately, though, we get a ratio value, and if that result is greater than 1.6, this
is interpreted to mean that the level of Borrelia-specific antibodies in the CSF is higher than those
in normalized serum, which is indicative of intrathecal synthesis and thus strongly suggestive
of neuroinvasive disease.
Importantly, determination of an AI is recommended by both the IDSA and the European Federation
of Neurological Sciences (EFNS) for diagnosis of neuroinvasive Lyme disease,
with the EFNS guidelines going further and outlining three criteria that must be met
to make a definitive diagnosis of Lyme neuroborreliosis, including the presence of neurologic symptoms
consistent with neuroinvasive disease, CSF pleocytosis, and an elevated Borrelia AI.
Although multiple different methods and assays are used to establish a Lyme antibody index
across laboratories and between published studies, the general performance characteristics
of the Lyme AI are briefly summarized in this table.
When it comes to sensitivity, it largely depends on when the patient presents clinically.
In patients with less than 6 weeks of symptoms, sensitivity ranges from roughly 70% to 90%
across studies, whereas in individuals with more than 6 weeks of symptoms, the sensitivity
of this method approaches 100%, and specificity is similarly high around 95%.
There are some caveats to keep in mind with the Lyme AI, including the fact that it will
be positive for a long period of time, and in many cases, this positivity can last beyond
six months following successful treatment, so the Lyme AI shouldn’t be used as a test
of cure, similar to the recommendations for standard serum serology.
Additionally, this is still a serologic-based assay, and cross-reactivity can occur with
other infections, most notably with neurosyphilis or infection with other Borrelia species,
so results really need to be interpreted alongside clinical presentation and exposure risk.
To help guide both clinicians and laboratorians with respect to the Lyme AI test offered through
Mayo Medical Laboratories, please refer to the Lyme neuroborreliosis diagnostic algorithm
shown here, which can be found on the MML website.
Thank you for your attention.