Chapter 25 - Infectious diseases of the central nervous system

Questions

Define the following terms:

meningitis, encephalitis, hydrocephaly (communicating and internal), meningismus, Kernig's sign, pleocytosis, Brudzinski's sign, parameningeal.
Meningitis is inflammation or infection of the meninges.
Encephalitis inflammation or infection of the brain.
Hydrocephaly (communicating and internal) is accumulation of cerebrospinal fluid due to deficient resorption (communicating) or obstruction of the flow pathway through the brain (internal). Hydrocephaly ex-vaccuo is when the brain shrinks and CSF replaces it.
Meningismus is resistance to neck flexion due to pain when inflamed meninges are stretched.
Kernig's sign is involuntary flexion of the knee when the lower limb is flexed at the hip. This occurs because the inflamed meninges are stretched by stretch of the sacral nerve roots.
Brudzinski's sign is involuntary flexion of the knees when the neck is flexed. This occurs because the inflamed meninges are stretched by flexing the neck and tension can be relieved somewhat by taking tension off of the sacral nerve roots by flexing the knees.
Pleocytosis is the presence of an excessive number of white blood cells in the spinal fluid.
Parameningeal refers to processes (particularly infections) that occur outside of the dura but which are adjacent to it (producing some signs - particularly in the CSF) of inflammation.


25-1. What broad classes of meningitis are there (name 4)?

Answer 25-1. Meningitis may be acute or chronic, bacterial or aseptic.

25-2. What are the most common causes of acute meningitis?

Answer 25-2. Most acute meningitis is bacterial or viral (chemical meningitis is rarer).

25-3. What are the most common causes of acute bacterial meningitis?

Answer 25-3. The most common cause of acute bacterial meningitis are strep pneumonia, Neisseia meningitides, group B strep, Listeria monocytogenes, Hemophilus influenzae.

25-4. Which bacterial would you suspect in adults? In older children/adolescents? In young children? In infants? In the elderly?

Answer 25-4. The most common organism producing meningitis: strep pneumonia (especially in adults); Neisseria meningitis (In children and young adults); group B strep (In infants); H flu (In young children); Listeria (In elderly and immunosuppressed).

25-5. What are the signs and symptoms of acute bacterial meningitis?

Answer 25-5. The most common symptoms of acute bacterial meningitis are headache, fever, meningismus, confusion progressing to stupor, elevated intracranial pressure. Young children and particularly infants may not have fever or neck stiffness. Infants may have a bulging fontanelle.

25-6. What are some potential complications of meningitis?

Answer 25-6. Potential complications of meningitis include: cranial nerve palsy, hydrocephalus, stroke, seizure, abscess.

25-7. What is the most critical diagnostic procedure for suspected meningitis?

Answer 25-7. Lumbar puncture is critical for diagnosis and for determining the best treatment.

25-8. What are the findings in the CSF in acute bacterial meningitis?

Answer 25-8. Increased protein is nonspecific. Lymphocytes are most common with viral meningitis or some chronic infections while PMNs are numerous with most bacterial meningitis (but some may be present early in viral meningitis). Glucose (as a percentage of systemic blood glucose) may be low with bacteria or some chronic meningitis.

25-9. What are the principles of treatment of acute meningitis?

Answer 25-9. Do not wait for cultures - empiric antibiotics are used to cover potential organisms. A third generation cephalosporin + vancomycin are most common, but you should consider adding ampicillin if over 55 or immunocompromised. Steroids may be useful in children to cut down on complications (not sure about adults, but they are often used).

25-10. What is the most common cause of aseptic meningitis?

Answer 25-10. Most aseptic meningitis is viral.

25-11. What are the symptoms of aseptic meningitis?

Answer 25-11. The symptoms of aseptic meningitis include headache, neck stiffness, photophobia, viral syndrome.

25-12. What are the CSF findings in aseptic meningitis?

Answer 25-12. The CSF usually shows fewer than 500 WBC - some polys early then lymphocytes. There may be slight elevation of protein but glucose is usually normal.

25-13. What are causes of chronic meningitis?

Answer 25-13. The causes of chronic meningitis include atypical bacteria (mycobacteria), fungi, spirochetes (syphilis, Lyme) and parasites. It may also result from neoplasm (carcinomatous meningitis) - especially lymphoma.

25-14. What are the signs and symptoms of chronic meningitis?

Answer 25-14. The signs and symptoms of chronic meningitis include headache and mental status change. The patients are usually debilitated and have constitutional symptoms although there is usually no meningismus. It may result in damage to cranial nerves or cause hydrocephaly and stroke.

25-15. What is the key to diagnosis of chronic meningitis?

Answer 25-15. CSF is critical to diagnosis of chronic meningitis. Exam may be difficult due to number of causes.

25-16. What are parameningeal infections?

Answer 25-16. Parameningeal infections are outside the dura but adjacent to it (sinuses, otitis, mastoiditis, epidural empyema, epidural abscess - including the spine, osteomyelitis). These often result in elevated protein and mononuclear pleocytosis in the CSF.

25-17. What are the features of acute viral encephalitis?

Answer 25-17. Patients with acute viral encephalitis may have meningeal signs but patients are more encephalopathic (sleepy, stuporous, not thinking clearly).

25-18. What are the potential complications of acute viral encephalitis?

Answer 25-18. Potential complications of encephalitis include increased intracranial pressure, and seizures.

25-19. What are the potential causes of acute viral encephalitis?

Answer 25-19. Potential causes of acute viral encephalitis include many arboviruses (seasonal and some in epidemics) including the several types of equine encephalitis as well as West Nile virus. The most common sporadic encephalitis is Herpes simplex which is critical to recognize since it is treatable and is fatal in most untreated cases.

25-20. What are the potential causes of chronic encephalitis?

Answer 25-20. The most common causes of chronic encephalitis are viral - HIV, myxovirus (progressive multifocal leukoencephalopathy) or subacute sclerosing panencephalitis (the measles virus). Creutzfeldt-Jacob disease is a subacute infectious disease in which a prion is the infectious particle. This usually produces a subacute dementia with minimal signs of infection and no meningeal signs.

25-21. What are the causes of brain abscesses?

Answer 25-21. Brain abscesses may follow focal infections such as otitis media, sinusitis, mastoiditis, but it may also result from hematogenous spread (teeth, bacterial endocarditis, etc).

25-22. What are the symptoms of brain abscess?

Answer 25-22. The symptoms of brain abscess include headache and focal deficits. The patient may or may not show signs of systemic illness. Seizures may develop, requiring anticonvulsants.

25-23. What are the most common organisms in brain abscess?

Answer 25-23. Brain abscess are usually mixed infection including anaerobes. There is a cerebritis stage, encapsulation stage, and potential rupture (sometimes fatal).

25-24. What is the treatment for brain abscesses?

Answer 25-24. Empiric antibiotics are used in the cerebritis stage of brain abscess (third generation cephalosporin and metonidazole or chloramphenacol). The patient requires close observation and may require surgical drainage or aspiration when capsule forms.

25-25. What about lumbar puncture in brain abscesses?

Answer 25-25. Spinal taps are extremely dangerous in brain abscesses due to potential herniation when pressure is released below.