Lumbar puncture (LP) is the technique of using a needle to withdraw cerebrospinal fluid (CSF) from the spinal canal. CSF is the clear, watery liquid that protects the central nervous system from injury and cushions it from the surrounding bone structure. It contains a variety of substances, particularly glucose (sugar), protein, and white blood cells from the immune system.
Lumbar puncture, or spinal tap, is used to diagnose some malignancies, such as certain types of brain cancer and leukemia, as well as other medical conditions that affect the central nervous system. It is also used for injecting chemotherapy directly into the CSF. This type of treatment is called intrathecal therapy. Other medical conditions diagnosed with lumbar puncture include:
- viral and bacterial meningitis
- syphilis, a sexually transmitted disease
- bleeding (hemorrhaging) around the brain and spinal cord
- multiple sclerosis, a disease that affects the myelin coating of the nerve fibers of the brain and spinal cord
- Guillain-Barré syndrome, an inflammation of the nerves
In some circumstances, a lumbar puncture to withdraw a small amount of CSF for analysis may lead to serious complications. Lumbar puncture should be performed only with extreme caution, and only if the benefits are thought to outweigh the risks, in certain conditions. For example, in people who have blood clotting (coagulation) or bleeding disorders or who are on anticoagulant treatment, lumbar puncture can cause bleeding that can compress the spinal cord. The term for this condition is spinal subdural hematoma, and it is a rare complication. However, it is of concern to some cancer patients whose low platelet counts (thrombocytopenia ) make them more susceptible to bleeding. In some cases, these patients are given a platelet transfusion prior to lumbar puncture, but this procedure is still under investigation. A 1984-88 study, supported in part by the National Cancer Institute, researched the risk of lumbar puncture on children with acute lymphoblastic leukemia (ALL). No serious lumbar puncture complications were observed in this study of over 5, 000 children.
A traumatic lumbar puncture (TLP) occurs when a blood vessel is inadvertently ruptured during the procedure. If this happens as part of a diagnostic leukemia workup, there is the potential of contaminating the CSF specimen that has been removed with leukemia cells, causing a false positive test result.
If there is a large brain tumor or other mass, removal of CSF can cause pressure shifts within the brain (herniation), causing compression of the brain stem and other vital structures, and leading to irreversible brain damage or death. These problems are easily avoided by checking blood coagulation through a blood test and by doing a computed tomography scan (CT) or magnetic resonance imaging (MRI) scan before attempting the lumbar puncture. In addition, a lumbar puncture procedure should never be performed at the site of a localized skin infection on the lower back because the infection may be introduced into the CSF and may spread to the brain or spinal cord.
In a lumbar puncture, the area of the spinal column used to obtain the CSF sample is in the lumbar spine, or lower section of the back. In rare instances, such as a spinal fluid blockage in the middle of the back, a doctor may perform a spinal tap in the neck. The lower lumbar spine (usually between the vertebrae known as L4-5) is preferable because the spinal cord stops near L2, and a needle introduced below this level will miss the spinal cord and encounter only nerve roots, which are easily pushed aside.
A lumbar puncture takes about 15-30 minutes. Patients can undergo the test in a doctor's office, laboratory, or outpatient hospital setting. Sometimes it requires an inpatient hospital stay. If the patient has severe osteoarthritis of the spine, is extremely uncooperative, or obese, it may be necessary to introduce the spinal needle using x-ray guidance.
In order to get an accurate sample of cerebrospinal fluid, it is critical that a patient is in the proper position. The spine must be curved to allow as much space as possible between the lower vertebrae, or bones of the back, for the doctor to insert a lumbar puncture needle between the vertebrae and withdraw a small amount of fluid. The most common position is for the patient to lie on his or her side with the back at the edge of the exam table, head and chin bent down, knees drawn up to the chest, and arms clasped around the knees. (Small infants and people who are obese may need to curve their spines in a sitting position.) People should talk to their doctor if they have any questions about their position because it is important to be comfortable and to remain still during the entire procedure. In fact, the doctor will explain the procedure to the patient (or guardian) so that the patient can agree in writing to have it done (informed consent). If the patient is anxious or uncooperative, a short-acting sedative may be given.
During a lumbar puncture, the doctor drapes the back with a sterile covering that has an opening over the puncture site and cleans the skin surface with an antiseptic solution. Patients receive a local anesthetic to minimize any pain in the lower back.
The doctor inserts a hollow, thin needle in the space between two vertebrae of the lower back and slowly advances it through ligamentous tissues toward the spine. A steady flow of clear cerebrospinal fluid, normally the color of water, will begin to fill the needle as soon as it enters the spinal canal. The doctor measures the cerebrospinal fluid pressure with a special instrument called a manometer and withdraws several vials of fluid for laboratory analysis. The amount of fluid collected depends on the type and number of tests needed to diagnose a particular medical disorder.
In some cases, the doctor must remove and reposition the needle. This occurs when there is not an even flow of fluid, the needle hits bone or a blood vessel, or the patient reports sharp, unusual pain.
Patients can go about their normal activities before a lumbar puncture. Experts recommend that patients relax before the procedure to release any muscle tension, since the lumbar puncture needle must pass through muscle tissue before it reaches the spinal canal. A patient's level of relaxation before and during the procedure plays a critical role in the test's success. Relaxation may be difficult for those patients who face frequent lumbar punctures, such as children with leukemia. In these cases, it is especially important for the child to receive psychological support before and after each procedure. It may be helpful to praise a child who remained still and quiet during the procedure, and to remind the child of his or her good behavior before the next lumbar puncture.
After the procedure, the doctor covers the site of the puncture with a sterile bandage. Patients must avoid sitting or standing and remain lying down for as long as six hours after the lumbar puncture. They should also drink plenty of fluids to help prevent lumbar puncture headache, which is discussed in the next section.
The most common side effect of lumbar puncture is a headache. This problem occurs in 10-20% of adult patients and in up to 40% of children. It is caused by decreased CSF pressure related to a small leak of CSF through the puncture site. These headaches usually are a dull pain, although some people report a throbbing sensation. A stiff neck and nausea may accompany the headache. A lumbar puncture headache typically begins within a few hours to two days after the procedure and usually persists a few days, although it can last several weeks or months.
In some cases, the headache can be prevented by lying flat for an hour after the lumbar puncture, and taking in more fluids for 24 hours after the procedure. Since an upright position worsens the pain, lying flat also helps control the pain, along with prescription or non-prescription pain relief medication, preferably one containing caffeine. In rare cases, the puncture site leak is "patched" using the patient's own blood. People may also experience back pain.
Patients who receive anti-cancer drugs through lumbar puncture sometimes have nausea and vomiting . Intrathecal methotrexate can cause mouth sores. Some of these symptoms may be relieved by anti-nausea drugs prescribed by the physician.
People should talk to their doctors about complications from a lumbar puncture. In most cases, this procedure is safe and effective. Some patients experience pain, difficulty urinating, infection, or leakage of cerebrospinal fluid from the puncture site after the procedure.
Normal CSF is clear and colorless. It may be straw or yellow-colored if there is excess protein, which may occur with cancer or inflammation. It may be cloudy in infections; blood-tinged if there was recent bleeding; or yellow to brown (xanthochromic) if caused by an older instance of bleeding.
A series of laboratory tests analyze the CSF for a variety of substances to rule out cancer or other medical disorders of the central nervous system. The following are normal values for commonly tested substances:
- CSF pressure: 50-180 mmH2
- Glucose: 40-85 mg/dL
- Protein: 15-50 mg/dL
- Leukocytes (white blood cells) total less than 5 per mL
- Lymphocytes (specific type of white blood cell): 60-70%
- Monocytes (a kind of white blood cell): 30-50%
- Neutrophils (another type of white blood cell): none
Normally, there are no red blood cells in the CSF unless the needle passes though a blood vessel on route to the CSF. If this is the case, there should be more red blood cells in the first tube collected than in the last.
A lumbar puncture is sometimes used as part of a diagnostic cancer workup. Abnormal test result values in the pressure or any of the substances found in the cerebrospinal fluid may suggest a number of medical problems including a tumor or spinal cord obstruction; hemorrhaging or bleeding in the central nervous system; infection from bacterial, viral, or fungal microorganisms; or an inflammation of the nerves. If there is a tumor in the meninges (membranes around the brain and spinal cord), the CSF may have higher protein levels, lower glucose levels, and a mild increase in lymphocytes (pleocytosis). It is important for patients to review the results of a cerebrospinal fluid analysis with their doctor and to discuss any treatment plans.
See Also Acute lymphocytic leukemia (ALL); Brain and central nervous system tumors
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Gajjar, Amar et al. "Traumatic lumbar puncture at diagnosisadversely affects outcome in childhood acute lymphoblastic leukemia." Blood 15 (November 2000): 3381-84.
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Martha Floberg Robbins
QUESTIONS TO ASK THE DOCTOR
- What is the purpose of my lumbar puncture?
- What aftercare will be needed?
- Will lumbar puncture be used for chemotherapy, and if so, how often will I receive treatments?
- What are the risks for diagnostic procedures or treatments through lumbar puncture?
- What do the test results mean?
- What techniques are suggested to relax children before and after a lumbar puncture?
Acute lymphoblastic leukemia (ALL)
—A type of leukemia, also called acute lymphocytic leukemia, primarily in children, affecting lymphocytes.
—An inflammation or infection of the brain and spinal cord caused by a virus or as a complication of another infection.
—An inflammation involving nerves that affects the extremities. The inflammation may spread to the face, arms, and chest.
—Protects the body against infection.
—Injecting chemotherapy directly into the CSF using lumbar puncture.
—A device used to measure fluid pressure.
—An infection or inflammation of the membranes or tissues that cover the brain and spinal cord, and caused by bacteria or a virus.
—A disease that destroys the covering (myelin sheath) of nerve fibers of the brain and spinal cord.
—The cavity or hollow space within the spine that contains cerebrospinal fluid.
—Reduced platelet levels.
—The bones of the spinal column. There are 33 along the spine, with five (called L1-L5) making up the lower lumbar region.