This is a procedure done by a physician to check cerebrospinal fluid (CSF) pressure, and to take a sample of CSF. It is done on the lower part of the spine.
What are usual reasons to do an LP?
It is usually performed for investigation of following conditions:
- Meningitis
- Encephalitis (brain infection)
- Sub-arachnoid hemorrhage
- Normal Pressure Hydrocephalus, a condition in elderly
- Idiopathic Intracranial Hypertension, a condition related to obesity
- For anesthesia purpose, during surgery or for childbirth (epidural)
- Diseases like multiple sclerosis, or neuropathy
How is the procedure done?
It can be done with patient on the side curled up like a baby, or sitting with head bent down, or flat with belly down. Lower lumbar area is cleaned with an antiseptic solution and draped. Using a small needle, a few cc of local anesthesia is injected in the spot between two vertebrae. Once the area is numb, a spinal needle is introduced, and the spinal fluid (CSF) cavity is approached. Once there, a plastic tube is attached to the needle to check the CSF pressure. After that, a few cc of CSF is collected in 3-4 tubes. Needle is removed, area is cleaned, and a bandage is applied.
Ideally, CSF pressure is checked every time an LP is done. In some patients though, it is the reason for the test, such as Idiopathic Intracranial Hypertension. For best measurement of CSF pressure, LP is done in left lateral recumbent position. Once the needle has approached CSF, legs and neck are slowly extended, and the patient is asked to relax and breathe normally. These measures are taken to avoid falsely high pressure.
In good hands, the procedure takes a few minutes. It may be little difficult in patients with obesity, especially if there is thick layer of fat above spine. In some patients it becomes difficult to locate vertebrae. Alternate option, is to involve a radiologist, and perform the procedure while visualizing the spine with x-ray. It is preferable to do it without x-ray to avoid unnecessary radiation exposure to the patient.
What may be the risk of LP?
Complications with LP are rare, while the most common complication is headache. Possible risks include allergy to local anesthesia, little bit of pain when local anesthesia is injected, low back pain, infection, leg pain and numbness, nerve injury, and headache that sometimes is severe and requires a similar procedure for treatment.
What is a spinal headache?
This is a headache that some patients have after an LP. Young and thin patients, especially women, are at higher risk of having this complication. Spinal headache is usually associated with dizziness, gets worse with sitting or standing, and gets better in flat position. It is considered to be due to low CSF pressure somehow due to the needle hole from LP.
How is spinal headache treated?
It can be treated with over-the-counter pain meds, hydration, with some caffeinated liquid. Usually, it resolves in 2-3 days. If it does not, a procedure called epidural blood patch is performed. In this procedure, the LP procedure is repeated at the previous spot, but instead of taking fluid out, a few cc of patient’s own blood is placed around that area, which, in principle, seals the original needle hole. Patients usually feel a dramatic improvement of their symptoms.
What are some misconceptions about LP?
. LP can damage the spinal cord: Spinal cord is not in the area where the procedure is done; risk to an injury to spinal cord is unrealistic.
. LP can cause paralysis: Unless, someone has no idea how and where this procedure is done, risk to a nerve is exceedingly rare. Nature has provided some interesting defense against this type of injury. Unlike a blood vessel, which can be easily punctured by a needle, it is not easy to damage a nerve. If the needle touches a nerve, it triggers sudden numbness, or tingling, or pain, and the needle is withdrawn. This in a way is an effective defense against accidental nerve injury. Also, unlike blood vessels, nerves are very slippery and malleable, and not easily punctured even with a needle.
. LP can cause permanent back injury and pain: There may be little bit of soreness for a day or two, but this procedure shall not injure any structure that may cause long-lasting back pain.
. LP is a very painful procedure: There is little bit of pain of needle that is used to deliver local anesthesia. After that, there should not be any pain, if there is, more anesthesia can be given.
What lab tests are performed on the CSF?
Usual testing involves checking the level of glucose and protein, number of red and white blood cells, and tests to rule out an inflammatory or infectious process. In some cases, more specific tests, including cytology are performed.
Where can I get more information about LP?
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