The lumbar puncture (LP) is a procedure that is performed by a physician to aid in the diagnosis of certain medical conditions. An LP is sometimes referred to as a “spinal tap,” and is done by inserting a needle in between the bones of the lower back (the “lumbar” region) and into the spinal canal. This procedure is performed to obtain a sample of cerebrospinal fluid (CSF) for laboratory testing.
CSF is the fluid that bathes the brain and spinal cord and helps to protect it from trauma or injury. It is composed primarily of water, glucose (sugar), and protein. Certain medical conditions can cause abnormalities in the CSF that can be detected through laboratory testing.
Conditions where an LP can aid in the diagnosis:
• Hemorrhage or bleeding into the brain
• Infections like meningitis, encephalitis, and brain abscess
• Inflammatory and autoimmune conditions like Multiple Sclerosis, Guillain Barre syndrome, and brain vasculitis
• Certain types of cancerous conditions
The amount of sample needed in a typical lumbar puncture is between about 10-30 mL of CSF. Not to worry, the average nervous system contains about 120 mL of CSF, and the brain is constantly replenishing and reabsorbing it at a rate of about 500 mL a day.
Proper positioning of the patient on the procedure table is the most important factor in obtaining a sufficient sample without contamination. The procedure can be performed with the patient sitting upright or lying on the side. In either position, the patient is bent forward at the waist with the knees tucked up toward the chest, and the head flexed forward with the chin toward the chest. In this position the bones of the lower back are flexed slightly to enlarge the openings between them, making it much easier for the needle to enter the spinal canal in the fewest number of attempts. When an LP is performed with X-ray guidance by a radiologist, the patient is sometimes positioned face down.
The risks of a lumbar puncture are relatively minor, and it is considered a safe procedure. A physician will advise a patient on the risks and benefits of the procedure specific to his or her case. Risks of the procedure can include bleeding, bruising, pain, infection, and headache.
The headache that can occur is an unusual headache that starts 0-24 hours after the procedure, is generally presents only when sitting or standing upright, and is relieved by lying flat. It can be mild or severe and is also known as a “spinal headache.” This symptom can often be minimized if the patient is encouraged to rest after the procedure, drink plenty of water the day of the procedure, and, if recommended by a physician, consume moderate amounts of caffeine.