Patient education: Lumbar puncture (spinal tap) (The Basics)

What is a lumbar puncture? — A lumbar puncture is a procedure doctors use to get a sample of fluid from around the spinal cord. It is also called an "LP" or a "spinal tap."

The spinal cord is a bundle of nerves that runs from the base of the brain down the back. Both the brain and spinal cord are surrounded by fluid called "cerebrospinal fluid." This fluid, also called "CSF," cushions and protects the brain and spinal cord. This fluid can hold important clues about the health of the brain and spinal cord. It can show, for example, if there is infection or bleeding in the brain.

Why might my doctor order an LP? — Your doctor might order an LP to check for problems that affect the brain or spinal cord. Some examples of these problems include:

●An infection that affects the brain or spinal cord, such as meningitis

●Bleeding in a part of your head called the "subarachnoid space" – This is the area between your brain and the thin layer of tissue that covers it. Bleeding in this area is called a "subarachnoid hemorrhage" (figure 1).

●A condition called multiple sclerosis, which causes vision problems, numbness and tingling, muscle weakness, and other problems

●Cancer that has spread to the tissues surrounding the brain or spinal cord

●Nerve problems such as Guillain-Barré syndrome, a condition that causes muscle weakness

●A condition called "pseudotumor cerebri," which can cause pressure inside the skull

Doctors sometimes also do LPs to give certain types of medicines directly into the area surrounding the spinal cord. Examples of medicines that might be given this way include:

●Anesthesia (to block pain, for example, during childbirth or surgery)

●Chemotherapy medicines (used to treat cancer)

●Antibiotics

What happens during an LP? — To get you ready for the LP, the doctor will probably ask you to lie on your side and hug your legs, so that your back is curved in a "C" shape. Sometimes, they might do the LP when you are seated. During the procedure, it is very important that you stay very still. Tell your doctor if you are uncomfortable or do not think you can stay still in the position they ask you to stay in. It is also important to let the doctor know if you feel any numbness, tingling, or other symptoms during the procedure.

Once you are in the right position, the doctor will feel your spine and choose where to do the LP. It will be in the lower part of your back, below the point where the spinal cord ends (figure 2). The doctor might also do an ultrasound to see where to place the needle. An ultrasound uses sound waves to create pictures of the inside of your body.

Before doing the LP, the doctor will clean the area around your lower back with a special liquid. They might also give you a shot to numb the area. Then the doctor will insert a needle into your back, between 2 of the bones (called "vertebrae") that make up the spine. The needle will go straight through your skin and the tissues that surround the spinal cord into the space that is filled with fluid.

After the needle is in place, the doctor will measure the fluid pressure. They will also collect a small sample of fluid, or inject medicine if needed. This generally takes several minutes. If the doctor needs to inject medicine, they will do this through the needle.

When the LP is done, the doctor will remove the needle and place a bandage over the area.

After doing the LP, your doctor might ask you to stay lying down for a half-hour or more, before you get up.

What are the downsides of having an LP? — Most people do not have problems after an LP. You should let your doctor know right away if you have unexpected symptoms. It's especially important to tell them if you have any numbness, tingling, or weakness of the legs, or if you have trouble urinating normally.

After having an LP, people can sometimes get a bad headache. This happens because the spot where the LP needle goes in does not always close up right away. If the hole stays open, CSF can leak out, causing a headache.

In most cases, the hole closes up on its own and the headache goes away in 1 to 2 days. If you get a headache after having an LP, you can take pain medicines to deal with it. The headache will also probably feel much better if you lie down. If your headache does not get better after 1 or 2 days, your doctors can offer you a treatment called a "blood patch." This involves taking a small amount of blood and injecting it into the area where the LP was taken. The blood fills in the hole and CSF levels go back to normal, so the headache goes away.

Rare problems caused by LP can include:

●Infection

●Bleeding – Before having an LP, tell your doctor if you take aspirin or an anti-clotting medicine. Anti-clotting medicines, also called "anticoagulants" or "blood thinners," are used to prevent blood clots. They include warfarin (brand name: Jantoven), apixaban (brand name: Eliquis), edoxaban (brand names: Savaysa, Lixiana), and rivaroxaban (brand name: Xarelto). These medicines could increase your risk of bleeding during the LP procedure. It's important for the doctor to know if you take them. They will also test your blood to make sure it clots normally.

●A life-threatening problem with the brain called "cerebral herniation" – This problem is very rare and usually happens only to people who already have a life-threatening brain condition.

●Pain or numbness in the back or legs

●Abnormal growths (called "epidermoid tumors") that form on the spine long after the LP is done – These is more likely to happen in children than in adults.

What if my child needs an LP? — LPs in children are very similar to LPs in adults, but children often must be given medicines to make them go to sleep before they have an LP. That's because children usually can't stay still the way they need to for an LP to be done the right way.

More on this topic

Patient education: Bacterial meningitis (The Basics)
Patient education: Viral meningitis (The Basics)
Patient education: Meningitis in children (The Basics)
Patient education: Idiopathic intracranial hypertension (pseudotumor cerebri) (The Basics)
Patient education: Hydrocephalus in babies and children (The Basics)
Patient education: Subarachnoid hemorrhage (The Basics)
Patient education: Spinal headache (The Basics)

Patient education: Meningitis in children (Beyond the Basics)