What is a lumbar puncture?
A lumbar puncture (LP), also known as a spinal tap, is a diagnostic and therapeutic procedure performed by a physician. The procedure is performed by inserting a hollow needle into the subarachnoid space in the lumbar area (lower back) of the spinal column. The subarachnoid space is the canal in the spinal column that carries cerebrospinal fluid (CSF) between the brain and the spinal cord.
CSF is a clear fluid that bathes the brain and spinal cord while protecting it, like a cushion, from exterior injury. The fluid is produced and reabsorbed in the brain on a continuous basis. CSF is composed of cells, water, proteins, sugars, and other vital substances that are essential to maintain equilibrium in the nervous system.
Reasons for the Procedure
A lumbar puncture may be performed for various reasons. The most common reason is to remove a small amount of CSF for examination and diagnosis of various disorders. CSF is tested for red and white blood cells, protein, glucose (sugar), clarity, color, and the presence of bacteria, viruses, or abnormal cells. Excess CSF may also be removed in patients who have an overproduction or decreased absorption of the fluid.
A lumbar puncture procedure may be helpful in diagnosing many diseases and disorders including, but not limited to, the following:
- Meningitis – an inflammation of the membrane covering the brain and spinal cord; The inflammation is usually the result of a viral, bacterial, or fungal infection, or the result of exposure to toxins or abnormal cells.
- Encephalitis – an inflammation of the brain that is usually caused by a virus
- Certain cancers involving the brain and spinal cord
- Bleeding in the subarachnoid space
- Reye syndrome – a potentially fatal disease that causes severe problems with the brain and other organs; Although the exact cause of the disease is not known, there has been an association between giving aspirin to children and the development of Reye syndrome. It is now advised not to give aspirin to children during illnesses, unless prescribed by your child’s physician.
- Myelitis – an inflammation of the spinal cord or bone marrow
- Neurosyphilis – a stage of syphilis during which the bacteria invades the central nervous system
- Guillain-Barré syndrome – a disorder in which the body’s immune system attacks part of the nervous system
- Demyelinating diseases – diseases that attack the protective coating that surrounds certain nerve fibers (e.g., multiple sclerosis or acute demyelination polyneuropathy)
- Headaches of unknown cause – After appropriate evaluation by a physician and appropriate head imaging if necessary, certain inflammatory conditions that can result in a headache may be diagnosed by lumbar puncture and CSF analysis.
- Pseudotumor cerebri (also called idiopathic intracranial hypertension, or IIH) – a condition in which pressure within the subarachnoid space is elevated for reasons that are still not clear; A lumbar puncture is only done in this condition after appropriate physician evaluation and head imaging.
- Normal pressure hydrocephalus – a rare condition affecting mainly older individuals in which there is a triad of loss of urinary control, memory problems, and an unsteady gait (ataxia); On head imaging, the normal spaces containing CSF in the brain are enlarged. A lumbar puncture is performed to see if the pressure of the CSF is elevated or not.
In addition, a lumbar puncture may be used to measure the pressure of the CSF, which flows freely between the spinal column and the brain.
The physician measures the pressure during a lumbar puncture using a special tube (called a manometer) that is attached to the lumbar puncture needle.
Finally, a lumbar puncture may be performed therapeutically to inject medications directly into the spinal cord. Some medications that may be given via lumbar puncture (intrathecally) include: spinal anesthetics before a surgical procedure, contrast dye for x-ray studies (e.g., myelography), or chemotherapeutic agents to treat cancer.
Potential Risks of the Procedure
Because this procedure involves the spinal cord and brain, the following potential complications may occur:
- A small amount of CSF can leak from the needle insertion site. This can cause headaches after the procedure. If there is a persistent leak the headache can be severe.
- Infection because the needle breaks the skin’s surface, providing a possible portal of entry for bacteria.
- Temporary pain or numbness to the legs or lower back pain may be experienced.
- Bleeding in the spinal canal
There may be other risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician prior to the procedure.
Before the Procedure
Your physician will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
- You will be asked to sign a consent form that gives your permission to do the procedure. Read the form and ask questions if something is not clear.
- Generally, fasting is not required prior to a lumbar puncture unless a sedative is prescribed. Your physician will instruct you prior to the procedure of any necessary fasting requirements.
- Notify your physician if you are pregnant or suspect you may be pregnant.
- Notify your physician of all medications (prescribed and over-the-counter) and herbal supplements that you are taking.
- Notify your physician if you have a history of seizures or if you are taking any prescribed medications for seizures.
- Notify your physician if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, or other medications that affect blood clotting. It may be necessary for you to stop these medications prior to the procedure.
- If the procedure is performed on an outpatient basis, you may be asked to remain in the hospital for several hours following the procedure. You should plan to have another person drive you home.
- Based upon your medical condition, your physician may request other specific preparation.