00:00 / 00:00








0 / 27 complete

USMLE® Step 1 questions

0 / 10 complete

High Yield Notes

13 pages



of complete


USMLE® Step 1 style questions USMLE

of complete

A 25-year-old man is brought to the emergency department by his partner following an episode of generalized convulsions. His partner reports that for the past 3 days, the patient has had a high fever and severe headache accompanied by nausea and vomiting. She also mentions that he started complaining of smell and taste changes. A few days ago, they came back from a trip to California in which they hiked and swam in lakes. Temperature is 38.9°C (102°F), pulse is 80/min, and blood pressure is 135/85 mmHg. On physical examination, the patient is confused and unresponsive. Pupils are equal and react sluggishly to light. Brudzinski sign is positive. A lumbar puncture is performed, and cerebrospinal fluid (CSF) analysis shows the following:  

 Cerebrospinal fluid 
 Opening pressure  300 mm H2
 Protein   130 mg/dL 
 Glucose  20 mg/dL 
 RBCs  Numerous 
 WBC count   1500/µL with polymorphonuclear predominance 
 Neutrophils   80%  

Gram stain of the CSF is negative. Head imaging results are nonspecific. Which of the following is the most likely causative organism?

External References

First Aid









meningitis p. 177


meningitis p. 177

Cryptococcus spp.

meningitis p. 177

Enterovirus meningitis p. 177

Escherichia coli p. , 143

meningitis p. 177, 727

Haemophilus influenzae type B

meningitis p. 177

Herpes simplex virus (HSV)

meningitis caused by p. 177

HIV (human immunodeficiency virus) p. 172

meningitis p. 177

Listeria spp.

meningitis p. 177


ceftriaxone p. 186

chloramphenicol p. 189

coccidioidomycosis p. 149

common causes p. 177

Cryptococcus neoformans p. , 150

CSF findings in p. 177

fluconazole p. 196

flucytosine p. 196

Haemophilus influenzae p. , 140

headaches with p. 536

HIV-positive adults p. 174

Listeria monocytogenes p. , 137

meningococci p. 140

mumps as cause p. 167

in neonates p. 181

rifamycin prophylaxis p. 193

Streptococcus pneumoniae p. , 134

Streptococcus agalactiae p. , 135

tuberculosis p. 138

unvaccinated children p. 183


meningitis p. 183

Neisseria meningitidis

meningitis p. 177


meningitis in p. 137, 181

Streptococcus agalactiae (Group B strep) p. 135

meningitis p. 177

Streptococcus pneumoniae p. , 134

bacterial meningitis p. 727

meningitis p. 177

Vancomycin p. 187

meningitis p. 177

Varicella zoster virus (VZV) p. 161, 487, 491

meningitis p. 177


With meningitis, mening- refers to the meninges which are three protective membranes that cover the brain and spinal cord, and -itis refers to inflammation; so meningitis is an inflammation of the meninges.

More specifically, it refers to the inflammation of the two inner layers which are called the leptomeninges.

The outer layer of the meninges is the dura mater, the middle layer is the arachnoid mater, and the inner layer is the pia mater.

These last two, the arachnoid and pia maters, are the leptomeninges.

Between the leptomeninges there’s the subarachnoid space, which houses cerebrospinal fluid, or CSF.

CSF is a clear, watery liquid which is pumped around the spinal cord and brain, cushioning them from impact and bathing them in nutrients.

In one microliter or cubic millimeter, there are normally a few white blood cells, up to 5.

If we look at a bigger sample, like say a decilitre, then around 70% of those will be lymphocytes, 30% monocytes, and just a few polymorphonuclear cells -- PMNs -- like neutrophils.

That same volume will contain some proteins, as well, about 15-50 mg as well as some glucose, about 45-100 mg, which is close to two thirds of the glucose we’d find in the same volume of blood.

The CSF is held under a little bit of pressure, below 200 mm of H2O, which is just under 15 mm of mercury -- which is less than a fifth of the mean arterial pressure.

Now at any given moment, there’s about 150 ml of CSF in the body.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Bacterial meningitis in children" The Lancet (2003)
  6. "Practice Guidelines for the Management of Bacterial Meningitis" Clinical Infectious Diseases (2004)

Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.