Pediatric Movement Disorders - Diagnostic Methods

Lumbar Puncture

In some cases, it may not be possible to accurately measure a particular chemical in the blood or it may be suspected that the concentration of a particular chemical in the brain is different from the concentration in the blood. In these cases, it is essential to measure concentrations in the cerebrospinal fluid (CSF). This fluid surrounds the brain and, because CSF is isolated from the blood, it may have a very different set of chemicals in it.

To obtain CSF, a small needle is inserted between the vertebrae in the lower back, at a level below the spinal cord. In this region of the spine, there are some nerves; however, these nerves are pushed out of the way by the needle and should not be damaged. The procedure is uncomfortable but not usually painful. It may take several attempts to find the correct spot.

When successful, fluid drips out of the needle and is sent for analysis. Complications with lumbar puncture (spinal tap) are rare. In some cases, imaging studies such as MRI, CT, or ultrasound must be done before the procedure.

Many tests may be performed on CSF. These tests include measurement of protein, glucose, and cell counts. In some cases, the glucose in the blood must be measured at the same time. This additional measurement helps to determine if there is a problem with transport of sugar into the brain or excess consumption of sugar in the brain. If infection is suspected, cultures may be ordered. Metabolic testing for lactate and amino acids may sometimes uncover disorders that were not measurable in blood. In addition, neurotransmitters and their metabolites may be measured. This additional information may be helpful in the diagnosis of certain metabolic diseases.