A spinal tap (lumbar puncture) is used to obtain a sample of cerebrospinal fluid from the sac that surrounds the spinal cord. The needle does not touch the spinal cord.

During a spinal tap, you will lie on your side or sit bent forward to open up the space between the vertebrae in your back as much as possible. After your skin is cleansed, you will receive an injection to numb the area. The technician will then insert a needle between two vertebrae in your lower back to remove a small amount of cerebrospinal fluid.

After a spinal tap, contact your physician if:

• You have a severe or prolonged headache.
• You spike a fever.
• You have intense pain in your back.
• You feel a tingling sensation in your groin or legs.
• There's a marked difference in your elimination habits.

A spinal tap may be used to diagnose or rule out certain neurological conditions, including:

• Amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease
• Central nervous system disorders
• Dementia
• Epilepsy