Snapshot A 25-year-old woman presents to the emergency department with left upper extremity weakness and urinary retention. The patient was admitted due to suspicion of multiple sclerosis and a lumbar puncture was performed. Cerebrospinal fluid demonstrated oligoclonal bands and an elevated IgG index. The patient subsequently developed a headache that is worse when sitting or standing and improves when lying flat in bed. (Positional orthostatic headaches from a cerebrospinal fluid leak caused by lumbar puncture). 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 elevated opening pressure in patients with idiopathic intracranial hypertension (pseudotumor cerebri) caution should be taken in performing the LP in patients with increased intracranial pressure from a space-occupying lesion the patient runs the risk of brain herniation thrombocytopenia or other bleeeding diathesis signs and symptoms concerning for a spinal epidural abscess Cerebrospinal Fluid AnalysisTestNormalBacterialViralFungal/TBOpening pressure≤ 20 cm H 2O↑normal or slightly ↑↑ColorClearCloudyClearCloudyCell count0-5 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 Complications Post-LP headache Infection Bleeding Cerebral herniation Traumatic lumbar puncture absence of xanthchromia declining red blood cell count in successive CSF collection tubes cerebrospinal fluid white -to-red blood cell ratio of 1:750-1000