A lumbar puncture, also known as a spinal tap, involves inserting a thin needle into the spinal cord between the lumbar bones (vertebrae of the lower back) to extract a small amount of cerebrospinal fluid (CSF) — the clear and protective watery liquid surrounding the brain and spinal cord.
How is the CSF useful in diagnosing AADC deficiency?
Aromatic L-amino acid decarboxylase (AADC) deficiency is a genetic disease caused by mutations in the DDC gene, which is responsible for the production of the AADC enzyme. This enzyme is needed for the production of important neurotransmitters (chemicals that transmit messages from nerve cells to muscles and other organs), such as dopamine and serotonin.
Insufficient AADC enzyme levels affect dopamine and serotonin production, resulting in poor communication between the central nervous system and the rest of the body.
The CSF is a mixture of several metabolites, including neurotransmitters. Measuring the levels of neurotransmitters that include dopamine and serotonin in the CSF helps to determine whether a person has AADC deficiency. CSF analysis also helps in ruling out (or confirming) the presence of any disorder apart from AADC deficiency.
How is a lumbar puncture performed?
A lumbar puncture is generally performed in an outpatient facility. Prior to the procedure, the doctor may advise the patient on food and drinks to consume or not to consume, and on the use of medications.
The procedure starts with a local anesthetic, given to numb the sensation of pain in the lumbar area. A thin, hollow needle is then inserted between two lumbar bones and the CSF sample is drawn. The puncture site is covered with a bandage.
After the procedure, the patient will be asked to rest, lying flat on the back for up to an hour to minimize the chance of headaches. The bandage can be removed after about 24 hours.
The CSF sample is sent to a diagnostic laboratory for analysis of specific metabolites and neurotransmitters. The results usually take a few weeks to come back, following which a consultation is arranged with the doctor.
What are the associated risks?
Lumbar puncture is generally a low-risk procedure, but it does carry the risk of a few potential complications. These include:
- Headaches due to fluid leakage into surrounding tissues.
- Back pain that radiates down to the legs.
- Bleeding at the site of puncture.
- Possibility of infection.
- On rare occasions, compression of the brainstem (brainstem herniation).
Last updated: Sept. 13, 2019
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