Spinal Taps: A Critical Research Tool
The thought of a lumbar puncture—commonly known as an LP or spinal tap—can be downright scary. Most of us do not like to be poked with a needle anywhere, much less near or around our spinal cords. The poke itself, however, can be less frightening than the possible side effects of headache or infection. Although spinal fluid was once essential for an MS diagnosis, in the last decade it has taken a back seat to the MRI. While spinal taps can—in certain instances—still be helpful in diagnosing MS, it is becoming apparent that spinal fluid may play a key role in predicting individual disease course and is therefore a vital research tool.
The Rocky Mountain MS Center believes that spinal fluid may provide an underexplored reservoir of information about MS. At the MS Center at Anschutz Medical Campus, there are several ongoing research projects that are exploring how spinal fluid may provide additional clues about MS and other neurological disease. By making the process of obtaining spinal fluid easier and safer (detailed below), we hope to increase the number of patients willing to participate in exciting research through spinal taps.
The spinal cord consists of millions of strands of nerve fibers and is about the diameter of a human finger. It is connected to the brain and descends down the middle of the back through the protective boney column of vertebra we often refer to as the backbone. It is also surrounded by cerebral spinal fluid or CSF, which acts as a cushion to protect the nerve fibers from injury. A spinal tap is a procedure that allows physicians to collect and look at the fluid that surrounds the brain and spinal cord. During a spinal tap, a needle is carefully inserted into the spinal canal low in the back—in the lumbar area—and a sample of spinal fluid is withdrawn.
When a spinal tap is performed, a sample of the person’s blood is taken at the same time. The laboratory analysis of the spinal fluid is compared to that of the blood. In MS, generally spinal taps are used to determine the number of oligoclonal bands and the IgG index. These two values provide a measure of how active the immune system is in the central nervous system (CNS or brain and spinal cord). A spinal tap is considered “positive” if either the oligoclonal bands or IgG index are positive, as is the case of ~95 percent of MS patients, although the tests used in some clinical laboratories may be less sensitive.
Oligocloncal bands (which represent antibodies produced inside the brain), refer to bands that can be seen when fluid is run on a gel in the lab. In particular, physicians care about bands that are restricted to the spinal fluid, but are not found in the serum (blood that has had all of the cells removed). Today, physicians count oligoclonal bands by using immunofixation or isoelectric focusing—both sophisticated and sensitive methods. Due to their sensitivity, a positive test requires more bands than in the past, and varies depending on different labs. Previously, only one band was necessary for diagnosis; today that number may be as high as four. Other health problems, such as infection and tumors, can make the number of oligoclonal bands increase, but these do not remain high. In MS, they remain high and are persistent, and indicate inflammation in the brain. Patient history and MRI can help eliminate other causes and hone in on MS.
The IgG index measures the same thing in a different way because the index can be elevated and not form the bands mentioned above. IgG antibodies, also known as immunoglobulin G, are one type of antibody. With spinal taps, physicians are interested in discovering if antibodies are made primarily in the central nervous system (CNS). This is determined by comparing the levels of IgG in spinal fluid to serum levels. The blood brain barrier (BBB) separates the spinal fluid from the blood. When there are active lesions, the BBB is disrupted, which allows blood IgG to cross into the spinal fluid. In the lab, the integrity of the BBB can be measured by looking at albumin (a globular protein) levels in spinal fluid and serum. Albumin is only found in serum, not spinal fluid. If the albumin ratio is high in the spinal fluid, it means the protein is spilling into it from the blood, which implies a breakdown of the BBB. In a similar way, an MRI done with contrast also identifies areas of BBB disruption because the contrast material, (often gadolinium) seeps into the tissues and is evident on scans.
Spinal fluid samples help physicians when an MS diagnosis is in question. Additionally, spinal fluid may contain “biomarkers” about individual response to disease and treatments, which could be used for a variety of purposes. Researchers at the Rocky Mountain MS Center at Anschutz Medical Campus are involved in many of these areas. These include:
- Improve physicians’ ability to diagnose MS and other related conditions. This can mean diagnosing patients and getting them on therapy earlier, which is when drugs work best. This could also minimize the diagnostic process, which can take many years from some patients.
- Eliminate the guessing game as to what is going to be the best medicine for a particular patient, including whether they even need treatment or if they can be taken off treatment.
- Improve physicians’ ability to predict prognosis. This is because patients with a higher number of oligoclonal bands and higher IgG index tend to do worse over time. There is a lot of variability, however, and this information is therefore not currently very useful for individual patients.
MRI has proven to be helpful in answering some of the questions above, but there are limits to its power. Spinal fluid gives another view into the disease process. For example, because spinal fluid bathes the brain and spinal cord—and therefore reflects what is occurring there—it is possible to identify damage to immune cells involved by measuring specific protein levels.
If you would like more information about these research projects, please call 303-724-4644 or click HERE.
Rocky Mountain MS Center at Anschutz Medical Campus physicians and physician assistants (PAs) perform spinal taps with special needles to minimize side effects, which can include low-pressure headaches. They are different from most headaches in that they are positional, which means that they are worse with sitting or standing and better with lying down. They occur when spinal fluid leaks from the spinal canal into the surrounding muscle.
MS Center staff uses a new type of needle that is smaller than a typical needle and is shaped like a bullet tip with a hole on the side. The needles are the thinnest possible caliber—thinner than most needles used for blood draws—and are non-cutting. This means the tip pushes away the dura (covering of the spinal canal) fibers as opposed to cutting them. The smaller needle, which some say resembles a hair, requires the use of a guide needle, or cannula. The guide gets through the skin and provides support for the thin needle. The smaller gauge needle, which has a lot of bend to it, then goes through the spinal fluid sac. This method decreases the probability of developing a spinal fluid headache from as high as 30 percent to about .7 percent.
Infections are extremely rare and lower than with blood draws due to the use of sterilizing solutions and the needle’s longer length. Nerve damage is also extremely rare because the needle is placed in an area below where the spinal cord generally ends.
Additional links
- Read last month’s MS article – A New Approach to Bladder Health
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- March is MS Awareness Month – Learn how to get involved.