Central nervous system infections: Pathology review

8,408views

00:00 / 00:00

Questions

USMLE® Step 1 style questions USMLE

of complete

An 18-day-old boy is brought to the emergency department due to fever and irritability. The boy was healthy at birth; however, 2-days ago, he developed a fever and decreased appetite. In addition, the patient has become increasingly irritable. Blood testing reveals leukopenia and cerebrospinal fluid (CSF) analysis reveals low glucose concentration and elevated proteins. Gram culture of the blood and CSF is positive for Streptococcus agalactiae. Which of the following is true regarding this pathogen?  

Transcript

Watch video only

At the emergency department, 17-year old Mike is brought in by his parents. He has a fever, headache, and photophobia. On clinical examination, Mike has neck stiffness and Kernig and Brudzinski signs are positive. Lumbar puncture reveals a predominantly neutrophilic pleocytosis, elevated protein, and low glucose. Next to Mike is 27-year old Helen, who came in with a fever, headache, and confusion for the past 72 hours. Kernig and Brudzinski signs are negative. Head CT reveals patchy temporal lobe enhancements. Finally, there’s 60-year Lucia, who is brought by her family because of a seizure. She also complains of headache and has a mild fever. There’s no neck stiffness and Kernig and Brudzinski signs are negative. Two weeks ago Lucia had an episode of otitis media for which she was treated with antipyretics and analgesics. She has no history of epilepsy. Head CT reveals a single ring-enhanced lesion in the right temporal lobe.

Okay, so all 3 people suffer from a central nervous system infection. CNS infections include meningitis, which is when pathogens infect the meningeal layers; encephalitis, when the pathogens infect the brain parenchyma; meningoencephalitis, where the infection starts in the meninges and then spreads into the brain parenchyma; and abscess which is when pathogens wall themselves off in the brain.

Okay, so let’s take a closer look at the various forms of CNS infections, starting with meningitis. Meningitis can be caused by any pathogen that infects the meninges. When it’s caused by viruses, mycobacteria, fungi, or parasites, it’s called aseptic meningitis, because routine bacterial cultures of the cerebrospinal fluid are negative. The most common cause of aseptic meningitis is a group of viruses called enteroviruses, like echovirus and coxsackie virus. Despite viral meningitis being much more common, acute bacterial meningitis is more life-threatening. The bacteria that is most likely to be responsible will depend on the individual’s age. For example, in infants less than 3 months, the most common causes in descending order are: group B Streptococci, Escherichia coli, and Listeria monocytogenes. In adolescents 13 to 17 years old, the most common causes are Neisseria meningitidis, followed by Streptococcus pneumoniae, and Haemophilus influenzae. In non-adolescent children 3 months to 12 years and in adults, Streptococcus pneumoniae is the most common cause, followed by Neisseria meningitidis and Haemophilus influenzae. It’s also important to consider Listeria monocytogenes in adults over the age of 50 or those who are immunocompromised. Also, Staphylococcus aureus is more common in individuals with a history of neurosurgical procedures or trauma to the head. Other rare but extremely important bacterial causes include Mycobacterium tuberculosis, lyme meningitis, rocky mountain spotted fever, and neurosyphilis. These are separated from the other causes because they’re usually associated with a specific risk factor. For example, tuberculous meningitis’s biggest factor is traveling to an endemic area or working with a high risk population. Lyme meningitis is caused by the spirochete Borrelia burgdorferi, and individuals can have a history of travel to an endemic region like the Northeast of the United States. Finally, Rocky Mountain Spotted Fever is caused by Rickettsia rickettsii and is carried by the Dermacentor dog tick. It is endemic to Central and South America as well as the Southeast United States. Neurosyphilis is rare, but it can arise in individuals with a history of untreated syphilis, especially in immunocompromised individuals.

Sources

  1. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  2. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  3. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  4. "Neuropsychological Neurology" Cambridge University Press (2013)
  5. "Aseptic Meningitis and Viral Myelitis" Neurologic Clinics (2008)
  6. "Measles-induced encephalitis" QJM (2014)
  7. "Toxoplasmic encephalitis relapse rates with pyrimethamine-based therapy: systematic review and meta-analysis" Pathogens and Global Health (2017)
Elsevier

Copyright © 2024 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.

RELX