Overview Snapshot A 59-year-old man presents to the emergency department with altered mental status. The patient is accompanied by his wife who says that the patient had a fever and headache for the past few days. On physical exam the patient is oriented to person but not place or time. Photophobia and neck stiffness is present. A lumbar puncture is performed for CSF analysis and shows a lymphocytic pleocytosis with normal glucose and protein. A PCR of the CSF is positive for HSV-1, and he is started on intravenous acyclovir. (Viral meningitis caused by HSV-1) Introduction Lumbar puncture (LP) is a procedure where a spinal needle is advanced into the subarachnoid space in order to collect cerebral spinal fluid (CSF) the LP can allow the physician to determine the etiology of meningitis if the patient has a subarachnoid hemorrhage in the setting of a normal non-contrast head CT the presence of a malignancy affecting the central nervous system (e.g., leptomeningeal carcinomatosis) the presence of a demyelinating disease (e.g., multiple sclerosis) if the patient has symptoms concerning for Guillain-Barre syndrome caution should be taken in performing the LP in patients with increased intracranial pressure the patient runs the risk of brain herniation thrombocytopenia or other bleeeding diathesis signs and symptoms concerning for a spinal epidural abscess Complications post-LP headache infection bleeding cerebral herniation Cerebrospinal Fluid Analysis Test Normal Bacterial Viral Fungal/TB Opening pressure ≤ 20 cm H2O ↑ normal or slightly ↑ ↑ Color Clear Cloudy Clear Cloudy Cell count 0-5 cells/µL ↑ (PMN) ↑ (Lymphocytes) ↑ (Lymphocytes) Protein < 45 mg/dL ↑ Slighty ↑ ↑ CSF:Serum glucose > 0.6 ↓ Normal ↓ Technique Patient position lateral recumbent position preferred for accurate opening pressure measurement prone position better for fluoroscopy guided LP sitting upright Needle entry into the subarachnoid space at L3-4 or L4-5 interspace remember that the spinal cord ends in L1-2 thus there should not be any trauma to the spinal cord if properly performed In cases where there are unsuccessful attempts in obtaining CSF, imaging guidance can be used such as fluoroscopy ultrasound