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Old 04-12-2010, 11:10 PM   #1
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Default Differential Dx and Screening

I recently took Chad Cook’s Differential Diagnosis course on Educata, which I do recommend. The online format is nice and you have 90 days access to the course afterwards and their customer service was responsive. This course was also thought provoking and assimilating for me, upon which I’ll expand below.

Cook advocates for using tests and measures that have high sensitivity and low negative likelihood rations (valuable information gleaned from these tests are negative findings as they have low probability of false negatives) first to rule out conditions. Use tests and measures with high specificity and high positive likelihood measures (which have low probability of false positives and therefore are valuable when positive) second to rule in conditions that were not previously ruled out.

This functions to improve prior probability. Good stuff!

He also advocates using the QUADAS scoring method to explore the quality of the studies that describe sensitivity, specificity, and likelihood ratios. Several tests and measures have large variations in these descriptions across studies. His criteria is that anything scoring at or above an 8/13 have adequate quality and the study with the highest QUADAS score is the measurement description used. Jason, Rod, or anybody else who might have familiarity with this methodology, I’d love to know your thoughts on its validity.

Here are papers on QUADAS, here, here, and here.

He then goes through the tests and measures that have adequate sensitivity, specificity, likelihood ratios and come from studies with adequate QUADAS scores for the upper and lower quarter.

Beyond the validity of QUADAS scoring and the concept of ordering of tests and measures to improve prior probability, this is where the majority of my thoughts come in. He goes through a list of tests organized by what they might rule in our out, some of which I found to be meaningful, like pelvis fractures, and others not so much, like carpal tunnel syndrome, SIJ dysfunction, and disc generated LBP. It struck me that, beyond tests to rule in/out conditions, there also existed within his listed tests those that rule in/out a target for treatment but were not diagnostic in a meaningful way otherwise. They don’t identify any specific and meaningful condition, but instead identify a target of a certain treatment. The diagnostic label for these “conditions” is in fact a surrogate for “potentially a responder to ___” These made up the tests that I found to not be meaningful diagnostically.

In this article , Nortin Hadler spells out what he sees as the relevant concepts of informed consent. Relevant here are these 2:

Quote:
No diagnostic study should be performed unless the test is interpretable in a fashion that benefits the patient. The test must detect a specific abnormality, one that is highly likely to play a role in the current illness. Furthermore, the detection of such must lead to a clinically meaningful insight regarding prognosis, if not to therapy.
Quote:
No medical screening should be offered unless the screening test has been shown to be adequately accurate, the disease to be screened for is important, and something meaningful can be done if the result is positive
So, at this point I’ll ask how does clinically identified Carpal Tunnel Syndrome, Cervical or Lumbar Radiculopathy, Disc generated LBP, Thoracic Outlet Syndrome, SI jt. Dysfunction, Spinal hypo/hyper mobility, stand up to Hadler’s criteria for testing or screening?
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Old 04-12-2010, 11:34 PM   #2
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Cory-
Excellent post.
Intelligent use of validity indices is critical to using tests and measures appropriately.
To my knowledge the QUADAS scale is the most commonly used guidepost and I heard Chad Cook speak at AAOMPT on these issues - he was great.
Funny how poorly some of our most cherished tests do when rigorously studied.
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Last edited by Jason Silvernail; 04-12-2010 at 11:35 PM. Reason: iPhone meh
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Old 04-12-2010, 11:48 PM   #3
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Quote:
It struck me that, beyond tests to rule in/out conditions, there also existed within his listed tests those that rule in/out a target for treatment but were not diagnostic in a meaningful way otherwise. They don’t identify any specific and meaningful condition, but instead identify a target of a certain treatment. The diagnostic label for these “conditions” is in fact a surrogate for “potentially a responder to ___” These made up the tests that I found to not be meaningful diagnostically.
Doesn't that pretty much eliminate clinical prediction rules that guide treatment interventions (as opposed to diagnostic ones like the Ottawa ankle rule), then?

QUADAS didn't come up during my Diff. Dx course at UIndy for some reason, so I'm not familiar with it. We did, however, use the pre-test probability and a computation of the likelihood ratio to determine post-test probability as described in Cleland's Orthopedic Examination text. I'll have to take a look and see if the QUADAS method is somehow related to this process.

Great post!
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Old 05-12-2010, 12:02 AM   #4
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Cory,

Was the course you took a multi-media course or was it primarily a text based course?
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Old 05-12-2010, 12:04 AM   #5
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Multi-media. Power point slides set to Cook's voice over.
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Old 05-12-2010, 12:04 AM   #6
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I also took the online Diff Dx course. I was happy to see to the low +LR of palpation based SIJ tests (will be good to point that out to co-workers). I have disposed of many special tests based on that course and have found my evals becoming much more efficient.
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Old 24-02-2011, 04:10 AM   #7
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How the heck did I miss this last April??? Sorry about that Cory.
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Old 24-02-2011, 05:48 AM   #8
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No worries. Missing stuff is practically a hobby of mine.
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Old 25-02-2011, 02:46 AM   #9
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Hey Cory. I'm thinking of downloading this course (or at least parts of it). Were any specific modules that were most helpful?
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Old 25-02-2011, 05:41 AM   #10
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Depends on what you're after and some of it may not be new for you having just gone through your fellowship.

The upper and lower quarter specific modules were mostly a listing of the tests that had passed thier stated levels of acceptability for sensitivity, specificity, pos and neg likelihood ratios, and QUADAS scoring.

The foundational modules go through differences in types of clinical reasoning (like Gestalt for example) and the ordering of examination which I thought was quite good in terms of putting prior probability into practice.

I think Jon, Matt R., and Gary D. have all taken it as well. Chime in if you've anything to add guys.
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Old 25-02-2011, 06:16 AM   #11
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Matt shot me some good info on the course so much appreciated. I'm particularly interested in the diagnostic reasoning Cook proposes (especially the references he uses). I'll check out the foundational lectures as well.

Thanks.
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