What Is a Lumbar Puncture? A Guided Tour of a Commonly Misunderstood Procedure
Key takeaways:
A lumbar puncture is a procedure in which a needle is inserted into the lower back to collect a sample of cerebrospinal fluid (CSF).
By testing CSF, which protects the spinal cord and brain, lumbar punctures can help diagnose medical conditions like infection, inflammation, or bleeding in the brain.
Even though this procedure can sound scary, it’s relatively safe and easily tolerated.
A lumbar puncture (LP), sometimes referred to as a spinal tap, is a common procedure that is used to both diagnose and treat certain medical conditions. During the procedure, a small needle is inserted at the base of the spine to collect a sample of cerebrospinal fluid (CSF). This is a clear fluid that surrounds and protects the brain and spinal cord.
Here are some details about why lumbar punctures are helpful, how the procedure is performed, and what you can expect if you need to have one.
Why do I need a lumbar puncture?
A lumbar puncture is most commonly used to test for certain neurological conditions. It is sometimes part of an evaluation for symptoms like headache, confusion, numbness, or weakness in the arms and legs. Some of the conditions that it can test for are:
Infections: such as encephalitis (an infection in the brain) or meningitis (an infection of the tissue layer that lines the brain)
Bleeding in the brain: like the kind that comes from a broken blood vessel or aneurysm
Increased pressure in the brain: that results from conditions like idiopathic intracranial hypertension (formerly called pseudotumor cerebri)
Inflammation in the nervous system: such as multiple sclerosis or Guillain-Barré syndrome
Cancers: that involve the brain and spine
LPs can also treat medical conditions, like idiopathic intracranial hypertension. This condition is characterized by increased pressure in the brain that leads to severe headaches. Draining the CSF through an LP can reduce that pressure, and thus alleviate the headaches. LPs can also be used to deliver medicine, such as chemotherapy medicines for lymphoma or leukemia.
Living with MS: After being diagnosed with multiple sclerosis, one woman shares how she overcame her fear and anxiety sparked by the condition.
Detecting infection: Lumbar punctures are used to diagnose neurological conditions. But they’re also a critical way to help identify certain infections like meningitis.
Coping with a dementia diagnosis: Seeing a specialist can be intimidating, but it can also get you the support you need. This was the case for one woman after her husband was diagnosed with early-onset Alzheimer’s disease.
What happens during a lumbar puncture?
Given LPs are commonly used to test for conditions in the brain, it may seem strange that the procedure is performed on the lower back. This is because it is the safest and easiest place to collect the CSF. CSF is produced in the brain, but it flows all the way down to the bottom of the spine. And the good news is that the CSF flows beyond the lowest level of the spinal cord, so the fluid can be collected without getting close to the spinal nerves.
The procedure usually takes about 15 minutes or so, but most of that time is spent getting in the right position. A provider performs an LP with you laying on your side (curled up in the fetal position), or sitting on the edge of the bed with your head resting on a bedside table.
The provider performing the LP will then use their hand to feel around your lower spine to get a sense of the best place to insert the needle. The needle needs to pass between the bones of the spine (vertebrae) in order to get to the right space to collect the fluid, so it can take a little time to scout out the best place to insert the needle.
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Once you’re in the right position, and your provider has a good sense of the anatomy of your spine, the procedure can begin. These are the next steps:
Your provider will clean the lower back with an antiseptic liquid.
The provider will inject some numbing medicine just under the skin where they plan to insert the needle. This is similar to what they would do if you were getting stitches. This is so you don’t feel the LP needle during the procedure. This numbing injection might sting a little at first, but it will start getting numb quickly.
Once your skin is numb, the provider will insert a very thin needle into the lower back until it gets into the right space where the CSF is located. You won’t feel anything sharp or painful, but you may sense some pressure as the needle is inserted.
Once the needle tip is in the right space, your provider will collect a small amount of the fluid. This part can take 1 to 2 minutes because the needle is very small, and so the fluid flows through the needle slowly.
The provider then removes the needle, and the procedure is over.
In most cases, a provider can easily perform this procedure at the bedside. In some cases, it helps to do the procedure in a special room with an X-ray machine (called fluoroscopy). This allows the provider to take pictures of the spine so they know where to guide the needle. This can be particularly helpful in people who have abnormal anatomy of their spine, like from arthritis or prior spine surgeries.
What to expect before and after a lumbar puncture
There are some things you can do before a lumbar puncture to make things a little easier:
Stay hydrated. This is helpful for two reasons. Good hydration supports CSF production, which can make the procedure a little easier. It can also help prevent you from getting dizzy or lightheaded, which happens to some people with any procedure that involves a needle.
Wear loose and comfortable clothing. You will change into a hospital gown for the procedure, but you can still wear your underwear. It helps to have underwear you can pull down a little bit, so it doesn’t interfere with the procedure.
Review your medications. Some medications, like blood thinners, are often temporarily held before the procedure. Talk to your provider about your daily medications to know if you should skip them before your LP.
Practice some relaxation techniques. Any medical procedure can feel scary, but an LP is less scary than it sounds. And it’s not easy to sit or lay still when you feel anxious. It may help to take several slow deep breaths, use the restroom, and know the procedure will be over before you know it.
After the procedure, your provider may suggest you lay down for a little while. This can help prevent any dizziness you may experience when standing. It also may help prevent any headaches after the procedure (more on that next). It helps to take it easy and rest for the next day or so. Avoid any strenuous activity for about a week, so your body can recover and rebuild its CSF, though most daily activities are OK.
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What are the risks of a lumbar puncture?
Complications from a lumbar puncture aren’t very common, and the procedure is relatively safe. But there can be some side effects:
You may experience some pain during the procedure. Typically there’s no discomfort after the numbing medicine is injected. So let your provider know if you don’t feel numb. It usually just means you need a little more.
Some people experience temporary headaches after the procedure. These can occur from a small amount of CSF leaking from the area where the needle was inserted. The headaches improve once the area heals and the CSF stops leaking.
Though they are much more rare, there are some potential complications of an LP:
Bleeding: This can occur around the spine. This is more likely in someone whose blood can’t clot normally. It can be serious if it starts to press on the nerves in the area.
Infections: This can happen if there is bacteria on the skin or needle when it is inserted. But rest assured that LP equipment comes from a sterile kit, and your back is thoroughly disinfected before the procedure. So this is unlikely to happen.
Nerve injury: This is also very uncommon, given the procedure is performed below the level of the actual spinal cord. The risk for this increases in people whose spine anatomy is a little different.
The bottom line
A lumbar puncture is a common procedure. And it isn’t as scary as it sounds. It’s a useful test for diagnosing neurological conditions that cause headaches, weakness, or numbness. And it can even be used to treat some of these conditions. There are a lot of misconceptions about pain and risks of a lumbar puncture, but in reality it’s a safe procedure that causes minimal discomfort. And serious complications are very rare. Rest assured your providers will be there to talk you through every step of the procedure.
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References
InformedHealth.org. (2016). What happens during a lumbar puncture (spinal tap)? Institute for Quality and Efficiency in Health Care.
National Health Service. (2021). Lumbar puncture.
