CNS Infections and Neoplasms Flashcards
How can infectious agents reach the CNS? Which route its the most common?
- most common: hematogenous spread
- other routes: direct implantation (due to trauma), local extension (from the skull or spine), and via the peripheral nerves (rabies and herpes zoster)
What is meningitis? What are the three major types? Which is a major medical emergency?
- meningitis is the inflammation of the leptomeninges (pia mater and arachnoid mater) within the subarachnoid space; it also involves the ventricular system
- major types: pyogenic/bacterial, aseptic/viral, and tuberculous (chronic)
- pyogenic meningitis is a major medical emergency (fatal if left untreated); luckily, viral meningitis is much more common and less severe
What are the major agents involved in bacterial/pyogenic meningitis for different groups of patients?
- neonates: Escherichia coli, group B streptococci (mainly Strep agalactiae), Listeria monocytogenes, HiB, Streptococci pneumoniae, Neisseria meningitidis
- children: HiB (especially if unvaccinated), Neisseria meningitidis
- young adults: N. meningitidis, Strep pneumoniae
- older adults: Strep pneumoniae, L. monocytogenes
- open head trauma/surgery: Staphylococcus aureus
- (L. monocytogenes in age extremities, pregnancy, and immunocompromised; ingested from foods)
- (note that in neonates, the E. coli and group B strep are from the vaginal canal)
What causes brain abscesses? What symptoms and signs result?
- these are focal, discrete, walled-off lesions that are nearly always due to a bacterial agent (commonly, they occur secondary to bacterial endocarditis)
- these are SOLs (space occupying lesions) leading to progressive focal deficits and general signs related to raised ICP (morning headaches, papilloedema)
What is encephalitis?
- inflammation of the brain parenchyma; is usually viral
- this nearly always occurs with a meningeal inflammation (rarely occurs on its own) = viral meningo-encephalitis
- tends to be less severe and more self-limiting than bacterial meningitis
- common agents: HSV-1, CMV (in fetuses and immunocompromised), rabies, HIV (affects microglial cells and can progress from there), JC virus (causes progressive multifocal leukoencephalopathy/PML)
What is Creutzfeldt-Jakob Disease (CJD)?
- this is a rapidly progressive, deadly “infection” of the CNS with a prion
- initial subtle changes in memory progress to coma and death in just 7 months
- consider this in patients with rapidly developing and progressing dementia
Are primary or metastatic tumors more common in the CNS? Which primary malignant tumor is the most common? Most common benign?
- in the CNS, primary tumors are more common! (prevalence of each is actually about 50%)
- glioblastoma multiforme is most common malignant tumor in adults
- meningioma is the most common benign tumor in adults
Where does the CNS receive most of its metastases from? Where do malignant CNS tumors metastasize to?
- CNS gets metastatic disease from lungs, breasts, kidneys, skin, and GIT
- even the most highly malignant CNS tumors rarely metastasize outside the brain, let alone the CNS
- (however, medulloblastomas and ependymomas may seed into the CSF and enter the spinal cord/spine)
What are the key clinical features of pyogenic meningitis? What is the classic triad of symptoms for meningitis in general?
- classic triad: nuchal rigidity/stiff neck, headache, and photophobia
- also: rapid onset (12-24 hours), systemic signs of infection (fever, rash), altered mental state, seizures (20-40%) and increased ICP (raised ICP occurs in more than 90% of cases)
Major investigation for meningitis is lumbar puncture and CSF analysis - compare the CSF in bacterial and viral meningitis.
- bacterial: yellow and cloudy, raised pressure, MANY neutrophils, LOTS of protein, LOW glucose (less than 50% plasma levels)
- viral: clear, normal/raised pressure, raised lymphocytes, raised protein, normal glucose
What is the mortality rate of bacterial meningitis? How do we treat it? What are the most common residual deficits?
- mortality rate of 10-20% (20% w/ S. pneumoniae; 15% w/ L. monocytogenes; 3-7% w/ HiB, N. meningitides, or group B strep)
- immediately treat empirically (and then specifically if organism is found) with Vancomycin and Ceftriaxone w/ adjunctive Dexamethasone (to stabilize the BBB)
- add doxycycline during tick season, and ampicillin if neonate, elderly, immunocompromised (for Listeria monocytogenes)
- most common residual deficits are deafness, cognitive defects (retardation), and epilepsy
- note that there are vaccines for HiB, Strep. pneumoniae, Mycobacterium tuberculosis, Neisseria meningitidis, Strep. agalactiae
Neisseria meningitidis
- spread via saliva or aerosol droplets
- this organism is responsible for meningitis epidemics
- colonizes the nasopharynx and then spreads hematogenously to the CNS
- meningitis is commonly preceded by a sore throat
- associated with purpura fulminans (this severe rash is seen in any severe case of sepsis though) and with Waterhouse-Friderichsen syndrome (adrenal hemorrhage resulting in adrenal gland failure)
- there is a vaccine
What is the major cause of aseptic/viral meningitis?
- enterovirus (85-90%); specifically the coxsackievirus
- others: HIV, HSV, mumps
How common are noninfectious causes of meningitis? What are some major examples?
- these are very rare
- drugs (NSAID hypersensitivity)
- autoimmune disorders (SLE)
- neoplasm (metastatic carcinoma)
- chemical agents (anesthetics)
Why do neonates have the highest risk of developing meningitis? What are some other high-risk groups?
- neonates have poorly developed immune systems and relatively permeable BBBs
- other high-risk groups: children and immunocompromised patients
