Infectious diseases affecting the central nervous system are of four general types: meningitis, encephalitis, abscesses, and the spongiform encephalopathies. Meningitis is an infection of the layers covering the brain. Symptoms include headaches, stiff neck, fever, and vomiting. The majority of cases are caused by four bacteria these are true medical emergencies and will result in death if not treated in a timely fashion. Viral or aseptic meningitis is much milder than bacterial meningitis. It has some of the same symptoms headache, sometimes a stiff neck, but rarely loss of mental status. Most cases are caused by non-polio enteroviruses although HSV2, on first exposure or occasionally on recurrence, can also cause aseptic meningitis. Abscesses present with focal neurological deficits, and can be caused by a wide variety of bacteria. The spongiform encephalopathies are degenerative diseases caused by prions. A lumbar puncture is the most useful diagnostic procedure for the diagnosis of meningitis -- it can distinguish between viral and bacterial meningitis, both by its protein and glucose composition and the presence or absence of white cells and of stainable bacteria, and it is imperative that one be done if meningitis is suspected. It is, however, contraindicated when focal deficits are present because patients with brain abscess and asymmetric cerebral edema can suffer brain stem herniation following lumbar puncture.
The organisms causing most cases of bacterial meningitis are Hemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, and Listeria monocytogenes. Listeria is transmitted through contaminated food and infects mostly the immunosuppressed and the elderly. In a hospital situation, Gram negative rods, Staph. Aureus, and enterococcus are seen as causes of meningitis. Cases of Hemophilus influenzae are now, thankfully, quite rare, due to the use of a vaccine. Hemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis are transmitted through the respiratory route or are endogenous infections. These organisms can grow to high concentrations in the bloodstream due to their capsules which make them resistant to phagocytosis. Neonatal meningitis, transmitted vertically, is caused by a different spectrum of organisms: E. coli K, Streptococcus agalactiae (GroupB), Listeria monocytogenes, and HSV2. Most of these are transmitted as the baby passes through the birth canal, although Listeria is transmitted transplacentally.
Encephalitis is an infection of the cortical tissues caused by viruses. It is manifested by fever, nausea, vomiting, neurological deficits, strange behavior, and somnolence and can be caused by many ³arbo² viruses, rabies, and HSV1. Viral encephalitis is a very serious disease which, unfortunately, is only rarely treatable. These diseases can be caused by the equine encephalitis viruses, Eastern Equine Encephalitis, Western Equine Encephalitis, St. Louis Encephalitis, or West Nile, which are all transmitted by mosquitoes. HSV 1 can cause encephalitis which, luckily, does have a drug with which it can be treated. Rabies is an encephalitis that is virtually always fatal; polio can also have devastating consequences. Other viruses, such as measles, mumps, and chicken pox can also have complications that involve the CNS.
As indicated, abscesses are manifested by focal neurological deficits and can be caused by many bacteria which spread to the brain either hematogenously or from a contiguous infected site such as the middle ear. The spongiform encephalopathies were thought for a long time to be inherited diseases or transmitted iatrogenically in very rare cases or by cannibalism in other rare events, but all this changed with the advent of ³Mad Cow Disease². Ingestion of material from diseased cows is now known to cause degenerative disease in humans.
It is very important that you know how to recognize, prevent, and care for these diseases. Chapter 6, pp 177-211, of Infectious Diseases in 30 Days by F.S. Southwick (McGraw-Hill, 2003) discusses some of these diseases. After reading this, or the appropriate section in your microbiology text, you should be able to answer the following questions. The cases in this section cover several different CNS diseases and will give you a start to understanding them.
Question 1 - Single Best Answer
When should a lumbar puncture be done?
after a CAT scan after antibiotics have been given for a day any time you are considering one only after the patient has lost consciousness
Question 2 - Single Best Answer
What is the structure responsible for the blood-brain barrier?
pia mater dura mater tight junctions between endothelial cells in the brain lack of synapses between nerve cells in the brain
Question 3 - Single Best Answer
For which of the following is a vaccine NOT available?
Neisseria meningitidis Streptococcus pneumoniae Hemophilus influenzae type B Listeria monocytogenes more than one of the above
Question 4 - Single Best Answer
Nosocomial meningitis would most likely be caused by which of the following organisms?
E. coli Listeria monocytogenes Neisseria meningitidis Streptococcus pneumoniae
Question 5 - Single Best Answer
The most common entry to the brain for pathogens causing meningitis is from the
nasal sinuses middle ear blood skull fracture spinal nerves
Question 6 - Single Best Answer
In bacterial meningitis the concentration of glucose in the CSF is
normal higher than normal lower than normal
Question 7 - Single Best Answer
Contradictions to a lumbar puncture include
stiff neck papilledema focal neurological deficits AIDS more than one of the above
Question 8 - Single Best Answer
Mortality is highest for which of the following bacterial meningitides?
rabies Listeria Streptococcus pneumoniae Neisseria meningitidis Hemophilus influenzae
Question 9 - Single Best Answer
In treating bacterial meningitis it is always important to use an antibiotic that is
bacteriostatic bacteriocidal broad spectrum can cross the blood-brain barrier
Question 10 - Single Best Answer
The viruses causing most cases of aseptic meningitis are
cocksackie and echoviruses EEEV and WNV rabies viruses polio viruses HSV1 and HSV2
Question 11 - Single Best Answer
A fungus that can cause meningitis is
Histoplasma tricophyton Candida Cryptococcus
Question 12 - Single Best Answer
Transmission of rabies has occurred nosocomially through
solid organ transplants corneal transplants doctors that carry the disease asymptomatically blood transfusions A and B above all of the above