Wednesday, October 26, 2005

A brand new technology for distinguishing between viral and bacterial meningitis?

Gruntdoc and medGadget may like this: The latest issue of Clinical Infectious Diseases (the official journal of the Infectious Diseases Society of America) has a very provocative article on a new technique for identifying cases of meningitis. I don't generally discuss current medical research in this blog but this is just too interesting to pass up.

A major conundrum that all internists, family practioners, pediatricians and emergency medicine physicians often face is the accurate diagnosis of meningitis. When patients present in an emergency room with neck stiffness, fever and neurological complaints they almost always have to have a lumbar puncture. This is an unpleasant procedure whereby some cerebral spinal fluid (CSF) is removed from the back with a large needle.

This fluid is then sent to the hospital's lab for a variety of studies to determine if the patient has meningitis or not. The great majority of meningitis cases are caused by viruses and have relatively benign courses (headache, fever, etc.) with patients recovering fully. These patients often don't have to be admitted to the hospital.

Unfortunately, less frequent forms of meningitis are caused by bacteria or fungi and are life-threatening. Such cases are true medical emergencies and require intravenous antibiotics, careful monitoring and hospital admission to prevent devastating permanent damage or death.

The problem is that current laboratory studies don't do a very good job of rapidly distinguishing between these different types. Either the available tests lack sensitivity (they often fail to identify true bacterial illness) or they lack specificity (they often misclassify viral meningitis as the more dangerous bacterial) or they take too long to process the specimen to give prompt information.

The end result is that most physicians have a very low threshold for admitting and treating many cases of meningitis as though they were bacterial in nature. Inevitably, many patients with viral meningitis will be admitted and treated as though they had the bacterial or fungal form. Obviously, given the currently available technology, this is necessary to prevent even a small number of patients from assuming the risk of a catastrophic outcome.

The unfortunate consequence of this conservatism is a very high cost associated with admitting many patients with viral disease, treating them with expensive, potentially toxic antibiotics and needlessly scaring the bejesus out of them and their families. Wouldn't it be great if there was a highly accurate and very rapid test for discriminating these different disease entities?

Metabonomics to the rescue. No this isn't some failed theory of language education. As one definition I got from the internet, metabonomics is:

"The quantitative measurement of the dynamic multiparametric metabolic response of living systems to pathophysiological stimuli or genetic modification".

Does that clarify things for you? Yeah right!

In the setting of the above article, this means taking medical specimens and acquiring a examining the biological "signature" through the use of proton nuclear magnetic resonance and mass spectroscopy. These are very sophisticated machines that examine the physical properties of these specimens rather than their biological properties such as cell counts, antibody studies or bacterial/fungal cultures.

The authors took a group of lumbar puncture specimens that were drawn from 12 patients with bacterial meningitis, 11 with viral and 27 controls (healthy people). These samples were then subjected to the high tech methods they developed and their signatures are compared statistically with the signatures of known samples. The equipment they used accurately classified every one of the specimens. This corresponds to 100% sensitivity and 100% specificity. Clearly this is the holy grail of clinical testing.

Reportedly, this test can be performed very rapidly, certainly within the time frame of an emergency room evaluation and in theory could accurately classify patients. Decisions can then be made to admit and treat those few patients with true bacterial meningitis and perhaps discharge those with more benign viral disease. The equipment to perform these analyses is currently available and though representing a high capital investment is apparently cheap to maintain and operate making it potentially available to most hospital labs.

If the technique turns out to be successful (it is only in its earliest stages of evaluation) it could make a major contribution to emergency medicine. One can only speculate on other applications of this technology. According to one of my UCLA infectious disease colleagues, it is at least several years from validation but it is very interesting.

Thought you ought to know.


Anonymous Anonymous said...

Sounds promising! Thanks!


October 26, 2005 10:17 PM  
Anonymous Ruth said...

just wanted to leave a "manual trackback" to let you know i found your entry useful and mentioned it in my blog:

November 01, 2005 3:59 AM  

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