Subinternship Medicine · Year 4 · from Subinternship Medicine
Case 1: Lumbar Puncture with CSF Interpretation
Clinical Image
Source: Wikimedia Commons - Lumbar Puncture - CC BY-SA 4.0
Case Presentation
A 28-year-old previously healthy man presents with 2 days of severe headache, fever to 39.2 degrees Celsius, and photophobia. He is alert but appears uncomfortable, holding his neck stiffly. Physical examination reveals positive Kernig and Brudzinski signs. CT head without contrast shows no mass effect or midline shift. The sub-intern is asked to perform the lumbar puncture. After obtaining informed consent and explaining the risks (headache, bleeding, infection, nerve injury), she positions the patient in lateral decubitus with knees drawn to chest. She identifies the L4-L5 interspace at the level of the iliac crests, performs sterile preparation with chlorhexidine, and infiltrates local anesthesia from skin to periosteum. The spinal needle is inserted with stylet in place, bevel oriented laterally. A "pop" is felt as the needle passes through the dura. Opening pressure is measured at 28 cm H2O (elevated). CSF is cloudy. Four tubes are collected, each 2 mL. CSF analysis reveals: WBC 2,400/microL with 95% neutrophils, protein 185 mg/dL, glucose 28 mg/dL (serum glucose 110 mg/dL, ratio 25%). Gram stain shows gram-positive diplococci. The patient is immediately started on ceftriaxone 2g IV, vancomycin 1g IV, and dexamethasone 0.15 mg/kg for suspected pneumococcal meningitis. Blood and CSF cultures later confirm Streptococcus pneumoniae.
Key Learning Points
- Lumbar puncture contraindications: mass effect on imaging, coagulopathy (platelets less than 50,000 or INR greater than 1.5), skin infection at puncture site, hemodynamic instability
- Normal CSF: WBC less than 5, protein less than 45 mg/dL, glucose greater than 60% of serum; bacterial meningitis shows WBC greater than 1000 (neutrophil predominant), very low glucose, elevated protein
- Opening pressure is measured with legs extended in lateral decubitus; normal is less than 20 cm H2O
- Do not delay antibiotics for lumbar puncture if the procedure will be delayed; blood cultures should be obtained but treatment should not wait