• Central nervous system (CNS) infection (viral, fungal, or bacterial) or malignancy.
• Intracranial pressure or pseudotumor.
• Metabolic studies.
• Aminoacidopathies.
• Neurotransmitter disorders.
• Undiagnosed movement disorders.
• Undiagnosed infantile or pediatric epilepsy.
• Demyelinating disease (eg, multiple sclerosis).
• Placing the patient with the sacral plane vertical is key.
• The head of the patient should be on your nondominant side. (Left-handed physicians should place the patient in the left lateral decubitus position.)
• Use your nondominant thumb to palpate the spinous process of L4 and put your index finger on the iliac crest.
• Use your dominant hand to manipulate the needle.
• If positioning is felt to be correct, try rotating the needle 90 degrees.
• If cerebrospinal fluid (CSF) flows slowly, be patient.