What Can a Spinal Fluid Examination Tell Us?
So, you’ve scheduled a cerebrospinal fluid examination. You’re a little concerned about the procedure itself (don’t be – it’s a very routine process that’s only slightly more involved than your standard blood test), and you want to know what, exactly, you can find out from your results.
I’ve been a neurologist for over two decades, and I’ve performed thousands of spinal fluid examinations. Below, I’ll walk you through some of the key things I’m looking for and how we can use lumbar punctures to test for neurodegenerative diseases. Let’s get started.
What’s examined in cerebrospinal fluid?
When I perform a cerebrospinal fluid examination, I’m testing for a few things:
Your white blood cells
Regardless of your health concerns, I always test for white blood cells. These are found in your immune system cells – red blood cells, in contrast, come from your blood vessels, but we shouldn’t see too many red blood cells in your spinal fluid.
If you have a significant number of white blood cells relative to the number of red blood cells, you could have an abnormal inflammatory or infectious process in the works.
I see this occasionally, even in patients at risk of multiple sclerosis (MS) who may have a few more white blood cells in their spinal fluid than normal. But if a person suspected of having MS has a ton of white blood cells in their spinal fluid, they probably don’t actually have MS. There’s something else going on.
Protein level and glucose
Protein and glucose levels are essential when you have a bacterial infection. Bacteria like to gobble up glucose – or sugar – so low glucose levels are detected in bacterial infections. This indicates meningitis , and for the most part, I don’t see this in my neurology clinic. In terms of Amyotrophic Lateral Sclerosis (ALS) or Lou Gehrig’s disease, you can’t diagnose ALS from spinal fluid, but elevated protein is a supportive finding.
I always reserve one tube of spinal fluid for microbiology testing. I’m looking for bacteria – including tuberculosis (TB)-like bacteria, which we call mycobacteria – and fungus.
The pathologists that receive your spinal fluid will perform stains, examine the fluid under a microscope, and culture some of your spinal fluid.
Cerebrospinal fluid examinations for neurodegenerative diseases
Most of my patients undergo a lumbar puncture to test for one of two neurodegenerative diseases: MS and Alzheimer’s disease.
Testing cerebrospinal fluid for MS
If MS is the focus, I test for immunoglobulins in your spinal fluid present in a disproportionate amount to the immunoglobulins in your blood. These are called oligoclonal bands.
The 2017 revised McDonald criteria for MS claims oligoclonal bands are the main biomarker of MS, so that’s what I follow in my clinic. Because this is a comparative examination, I’ll need both your spinal fluid and blood.
We can do other tests on the spinal fluid for MS, like a myelin basic protein test, but most of these have gone by the wayside in recent years.
Alzheimer’s disease is the neurodegenerative condition that’s seen the most advancements in its biomarkers – changes we can identify in the fluid that are specific to a given disease.
When testing for Alzheimer’s, I am looking for amyloid protein or beta-amyloid 42, total tau protein, and phosphorylated tau. Beta amyloid protein is an inflammatory marker, which means anytime you have an inflammatory threat to your brain and body, amyloid levels go up. They can even go up if you’re sleep-deprived, for example. But when you catch up on your sleep, they tend to go down, unless you are chronically sleep deprived.
In the case of Alzheimer’s, amyloid forms an insoluble protein that builds up more and more. Eventually, a cascade of events occurs which causes nerve cells to break down and release, a protein called tau. It is something we also test for when examining spinal fluid for evidence of Alzheimer’s.
The goal is to catch people early. Incredibly changes occur in the brain ten to 20 years before the onset of symptoms related to Alzheimer’s disease. Using biochemical changes in the spinal fluid, I can diagnose early evolving Alzheimer’s in the preclinical state before a person has memory loss.
This is crucial because in the next three to four months, and then over the following few years, we’re going to see various treatments aimed at people in the preclinical or the early stage of the disease. Biogen Corporation is developing one treatment called aducanumab (which is the closest to becoming commercially available), and Lilly has another in the pipeline, called donanemab. I’m sure there’ll be others, too.
Essentially, these treatments make it even more vital to catch changes before they become a problem, before the tau protein causes nerve cell destruction. In other words, we want to phone the fire department before the house starts to burn to the ground. Putting out a small fire is a lot easier. If the house has turned to ash, it’s probably too late.
So, when testing for Alzheimer’s disease, I’ll take five tubes of spinal fluid – the typical kit comes with four, so it’s a little more than usual. I’ll measure your amyloid-beta 42 to 40 ratio. Amino acids are the building blocks of amyloid protein, and some amyloids are 40 amino acids long, and others are 42. The amyloid-beta 42 is the one that’s associated with Alzheimer’s disease, and a low ratio, as measured by the lab, suggests a high probability of Alzheimer’s.
Bear in mind, the 42/40 ratio is not diagnostic. Instead, it is a probability. It measures risk, which is helpful, but it’s not specific enough. That’s where tube five comes into play.
I’ll draw a few extra ml of spinal fluid and send that off to the lab. They will measure tau protein, total tau, phosphorylated tau, and amyloid levels. Using that data, they will create a graph using a calculation called the amyloid-tau index plotted against the amount of phosphorylated tau. If your result falls above a certain cut-off point, the findings are consistent with Alzheimer’s disease.
I know this sounds science-y but don’t worry. We’ll discuss the process and your results in a way that makes sense to you. The most important thing you can do is come see me if you suspect something is wrong with your memory because there’s no better time to take action to change your trajectory.
Re-routing your health’s trajectory
Are you ready to get the answers you’ve been looking for? Spinal fluid examinations are just one piece of the puzzle. I use a unique five-pillar system founded on a functional and regenerative medicine strategies that empowers you to regain control and reshape your future. At Sharlin Health and Neurology there are also research-based options, and, of course, the best that conventional neurology offers. Contact my clinic today to schedule an appointment.