Diagnostic Process Flashcards
what are the components of the diagnostic process
- information gathering
- integration and interpretation
- hypothesis
- gather more information
symptom
a manifestation of a disease as reported by the patient
sign
a manifestation of disease that the clinician observes
what is premature closure?
failing to consider reasonable alternatives after an initial diagnosis is made
evidence definition re: probabilities
information that helps you update your estimate probabilities
what is a disease illness script?
a representation of a condition in the mind of a practitioner
varies between practitioners
what are the components of a disease illness script
- epidemiology
- time course
- clinical presentation/syndrome
- mechanism or pathophysiology
syndrome definition
a set of signs and symptoms
what is included in epidemiology?
things that increase your risk
- demographics: age, sex, race, ethnicity, socioeconomic status
- risk factors or pre-existing conditions
- exposures (travel, hobbies, occupation, hobbies, drugs sexual, medications, pets)
what is included in time course?
duration and pattern (aka. persistence)
what is meant by duration?
duration can be: hyperacute, acute, subacute, or chronic
what is meant by pattern/persistence?
constant or episodic
what are some words that would describe a constant pattern?
stable, progressive
ex. something constantly getting worse
what are some words that would describe an episodic pattern?
waxing and waning (comes and goes); intermittent
what is included in clinical presentation aspect of a disease illness script?
the most important signs and symptoms
can use “classic” presentation but it can be misleading/lead to stereotyping
what are some features of high quality disease illness scripts?
- uses medical terminology and categories - it helps you to make better diagnostic decisions because you can categorize things appropriately
- they will change over time with experience and research
- multiple disease illness scripts can be compared/contrasted
does someone have to have all the signs and symptoms listed on a disease illness script to be considered for that condition?
no
problem representation definition
a representation of what’s going on with the patient that you want to match as closely as you can with a disease illness script
why is good problem representation important?
- you will have a more effective and precise diagnostic process if you have good problem representation
- also helps with researching possible treatments
steps to process patient information into a problem representation
create a problem list
process the list (emphasize the most valuable evidence and de-emphasize less valuable evidence; abstract patient concerns into medical terminology; process the list ie. put it into medical terms)
patient illness script definition
a concise representation of the patient’s concern that allows matching with a disease illness script
what are the components of a patient illness script?
- epidemiology
- time course
- clinical presentation (syndrome/signs/symptoms)
- other important medical history
how does a patient illness script differ from a SOAP note?
patient illness script won’t differentiate between subjective and objective but kind of combines them together
what is excluded in the clinical presentation aspect of a patient illness script?
- elements already mentioned in previous sections
- findings of little relevance
- past medical history that is unconnected to the chief complaint
- previous diagnosis - UNLESS they were clearly correct
differential diagnosis definintion
the process by which clinicians consider some possible causes of the patient’s signs and symptoms before making a final diagnosis
why is it important to come up with a differential diagnosis list?
if not done deliberately, people tend to fail to consider options after arriving at an initial guess
what is the availability heuristic?
the tendency to use information that comes to mind quickly and easily. It favours recent or more memorable experiences
are initial guesses or later guesses more subject to the availability heuristic?
initial guesses
why can we not make a list of all the possibilities instead of going through the differential diagnosis process?
- this is called possibilism
- technically impossible to do this as we are limited by our medical knowledge and time
- can lead to unnecessary testing/diagnostic work up
- people sometimes use mnemonics for generating differentials but they lead to very long lists
what is an emergent condition?
a condition that is an emergency,
it is NOT something that is emerging
what are the factors that we should consider when looking to make a differential diagnosis list?
probability - what is most likely
prognosis - which conditions are worse if left unconsidered
pragmatism - what conditions have the best benefit:harm ratio if treated
when do we start considering differential diagnoses?
generally after we are done gathering a bit of information about the chief concern
probability definition
how likely something is
how is probability expressed?
on a scale of 0-100% or 0-1 where 1=100%
is it possible to reach a probability of 100%?
No, we can never be completely certain
is it possible to reach a probability of 0%?
No, we can never be completely certain
are practitioners more likely to over estimate or under estimate probability of diagnosis before and after testing? what types of bias are present here? implications of this?
- they are likely to overestimate probability of diagnosis both before and after testing
- cognitive bias: base rate neglect, anchoring bias, confirmation bias
- implications: over testing, excessive medication and procedures
representativeness definition
the degree to which something is representative of, or similar to, the stereotype
when we are asked to judge probability, what do we often judge instead?
representativeness - whether someone fits into a certain category
T/F: an uncommon presentation of a common disease is more likely than a common presentation of a rare disease
true: if this weren’t so, diagnosis might be a matter of pattern-matching. we should think of the thing that is more common, not as much of the thing that matches the most
base rate definition
the base rate of a disease or a statistic that there is a certain ratio of something (ex 20:1 male farmers:male librarians in North America)
pretest probability
the best estimate of a disease probability before you do a test;
serves as a starting place from which to update probability
how to determine pretest probability
want to start with a good/best reference class
best reference class definition
the set of patients that most closely matches the patient at hand
reference classes that can be used as pretest probabilities
- prevalence of disease in a population
- studies that give eventual diagnosis in patients presenting with the complaints similar to your patients (this would be more specific than prevalence, less common/hard to find)
what should you NOT use as a reference class for pretest probability? why?
- incidence in the population because it’s the frequency fo a disease over a period of time
- lifetime prevalence - its the chance of developing the disease over a lifetime and will be an overestimate for pretest probability
likelihood ratio (LR) definition
a measurement of evidence strength
numbers that represent the value of the information a test provides
what does an LR of 1 mean?
it is useless because it does not change the probability
what does an LR >1 mean?
greater LRs increase the probability by more
what does an LR <1 mean?
LRs < 1 decrease the probability (they can go all the way down to zero)
what does an LR of 0 mean?
LR of zero tells us we can definitively rule out a condition
can you have an LR < 0?
No
Is a change is probability linear with the size of the LR?
No, there are diminishing returns
ie. if the LR doubles, it doesn’t mean that the probability will also double
what probability will have the most effect on what the post-test probability will be? Why?
the pre-test probability because the more extreme your initial probability (closer to 0 or 100%), the harder it should be to change your mind
what % probability is the most uncertain you can get?
50% certainty. Any lower and you’re more certain that the condition is not present
what is meant by “good” tests and “bad” tests?
tests can’t really be described as good or bad. A good test may mean it has valuable information if it’s positive, negative, or both but usually a test is only particularly good at ruling in or ruling out a condition and not both.
when do we look at the LR+ value?
when the finding is present
when do we look at the LR- value?
when the finding is absent
what is the equation for calculating LR+?
LR+ = sensitivity/ (1-specificity)
what is the equation for calculating LR-?
LR- = (1-sensitivity)/specificity
what is the SpPIN/SnNOUT mnemonic telling us?
a Specific test, if Positive, helps rule the condition IN
a Sensitive test, if Negative, helps rule the condition OUT
what should you do if you can’t find an LR?
you should be conservative with your estimates about a test’s value because people tend to overestimate the “diagnosticicity” of their evidence