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DIAGNOSIS

Slide 2: Diagnosis

Diagnosis: to be able to identify the disease.

This lecture deals with the basic principles to follow when interpreting diagnostic

tests

A diagnostic test is conventionally performed in a lab

In dentistry It can be performed chairside (in the dental clinic)

Pulp vitality testing, we can measure if the pulp of that tooth is vital or not at

the clinic; we dont have to go to the lab for that. Also sometimes we can do

diagnosis in the clinic in medicine as well.

It can also be obtained from history taking, physical examination and imaging

procedures.

Sometimes, the history itself can actually be considered as a test you do in

diagnosing some problems.

A patient is suffering from severe spontaneous pain and it is also provoked by

cold, and on cold it lasts more than few seconds and it awakes the patient from

his sleeping, and when we examined the tooth, we found that its badly decayed.

These findings based on the history taking and examinations are helpful in

telling that this tooth has irreversible pulpitis.

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Slide 3: Simplifying data

Clinicians generally reduce the data to a simpler form in order to make it useful in

practice.

Sometimes, we have to convert our data to very simple format, which also makes

the diagnosis more precise and help in making the treatment plan.

During examining a tooth I find that its mobile, but I cannot only say that this

tooth is mobile, I want to know the degree of mobility of that tooth; thats why

I need ordinal scale, I say this is grade 1, 2, or 3 mobility. And thats very

important, because people suffering from grade 1 mobility dont have to extract

the tooth, but people with grade 3 mobile tooth have to extract their tooth.

The scale can also be dichotomous, which means binary (two variables); like for

example, present or absence, normal or abnormal.

They often change interval scale to ordinal or nominal one

Last lecture caption: Interval scale: Also callednumericalordimensional, becaus e we use numbers in this scale Nominal scale: Giving names to different conditions , it's not strictly a scale, you are just giving

names.

Ordinal scale: Here we give words too, but in this scale we have some order and rankingBlood pressure, sometimes I dont want to know the actual reading of blood

pressure, I just want to know whether its high or low.

Heart murmur, it can be measured by a special device and it gives a reading in

interval scale, but I just want to know a scale from 1 to 4 (ordinal scale),

because I, as a DENTIST B-), may not understand the reading for heart

murmur (:O) , thats why I want it in ordinal scale, like from 1 to 4 so I can

understand it.

Slide 4-8: Gold standard

Is the sound assessment of the truth (to evaluate truth).

It is the certainty that the disease is truly present or absent

Establishing the diagnosis is imperfectthats why the diagnosis is not always

something certain; its something that has high probability.

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When I diagnose Maher (t7ammalna Dr.Maher), and my diagnosis showed that

he has a reversible pulpitis, am I 100% sure that he has reversible pulpitis? No,

I may be only 95% sure. So, thats why when I say that maher has this diagnosis,

this means that theres a very high probability that maher has that problem but

I cannot say that Im certain that maher has this problem.

Gold standard types of tests

Simple vs. elaborate

Simple tests are

Easier to perform Inexpensive But they are less accurate

Elaborate tests (which are tests that are done in the labs) are:

More expensive More accurate But more risky

Examples of simple and elaborate tests

Pulp vitality testing (simple) I want to measure the vitality of the tooth, its very simple and I can do it in the

clinic without paying a lot of money but my results may not be very accurate.

Throat culture for strep throat (simple)We just take a swab from the throat of the patient and send it to the lab, then

they quickly make a culture and they say if there are bacteria or not. Histopathology for lesions (elaborate)

A patient that you are treating has a lesion on the tongue and it looks like

cancer, you take biopsy and send it to the lab; and then the histopathologists

(like Dr. Rima and Dr. Huda Hammad here) will examine it under the

microscope and tell me that this is cancer. By this Im almost 100% sure that

this is accurate but its expensive and risky.

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A patient has angina pectoris, which might lead to myocardial infarction. The

easiest way to diagnose a patient with myocardial infarction is to do serum test

but the best way to get a very precise results is to take a biopsy from the

heart but I cant do it because its very risky.

Radiological contrast material (elaborate)Injecting certain material inside the blood vessel.

Autopsies: its the studying of a body of a dead person.However, advanced tests are not the tests of options most of the time.

More costly, less feasible and more risky Simpler tests can give adequate results without a risk (at least initially)

- Compromising accuracy is justified by minimizing the riskLike the myocardial infarctions example, the advanced test is to take a biopsy

from the heart but we dont do this, instead of that we take a serum sample, so,

we sacrificed with the accuracy at the expense of patients health.

Examples

It is easier to diagnose pneumonia with chest x-ray and sputum smear ratherthan lung biopsy

ECG and Serum Enzyme rather than heart biopsy, catheterization or imagingas in case of MI

It is easier to establish diagnosis with simpler tests with understanding that there is a

risk of diagnosis.

Therefore we are going to describe the value of diagnostic tests.

Slide9: Accuracy of test results

Establishing a diagnosis is aprobability rather than a certainty.

- We commonly use possible: or rule outSometimes we say that this person probably has this disease; other times we can

rule out ( ) some diseases.Clinicians should be familiar with mathematical relationships between the properties

of diagnostic tests and the information they have about them.

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Slide 10: Accuracy of test results

Sometimes the disease is present or absent. And tests can be positive or negative.

Vitality of the tooth, I want to examine whether this tooth is vital or not. Lets

suppose that we have pulpitis (the disease is present), and I did a test and it

shows that this tooth has pulpitis, this is considered True Positive. But if the

tooth has pulpitis and for any reason the test shows negative result, itll be

considered False Negative. Now, the other situation, a person doesnt have any

problem, and I examined his tooth for vitality testing but it gives a positive

result, thats called False Positive. Now, when the person also has a tooth with

no problems and the test gives a negative result, we call this True Negative.

What are the things that I want? (Actuall y I dont know what the dr. meant with this sentence)

1. True positive.

2. True Negative.

Slide 11-17: Sensitivity and specificity

Sensitivity

The proportion of people who tested positive for the disease from those whohave the diseaseSo, if we say that this vitality test is sensitive, it should all

the time produce a positive result when the person has the disease, and it

shouldnt show a negative result for that person.

High sensitive test will rarely miss people with the disease,If the test has low sensitivity, this means that we have people who are

abnormal but they tested normal.

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Specificity:

The proportion of people who tested negative for the disease from thosewithout the disease

In specificity, normal people should always give negative results, and these people

shouldnt show positive results.

High specific test will rarely miss people withoutthe diseaseSo, if anybody without the disease tested positive, that means that this test is not

specific.

Sensitivity is (a/a+c); so, those who tested true positive at the proportion from all

the people who have the disease.

Specificity is (d/b+d); so, those people who tested true negative from all the people

who doesnt have the disease.

The prevalence is (a+c/a+b+c+d); so, people with a present disease over the whole

people.

Example:

37 of 149 patients with sore throats were diagnosed as having pharyngitisand receive Antibiotics

Only 27 of those had positive culture for streptococcus The remaining 112 with sore throats were not diagnosed as having

pharyngitis and were not given Antibiotics

Of the those 112, 77 had negative cultures for streptococcus

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Sensitivity= a/a+c = 27/27+10 = 27/37 = 73% Specificity= d/b+d = 77/35+77 = 77/112=69% Prevalence= a+c/a+b+c+d = 37/149 = 25%

NOTE: Slide (17-20) was the first part of lecture 8 which is unfortunately missing! So I put acaption from the last year lecture to understand it more, put in your mind that the slides

were different last year, the Dr. was different too. (Dr. 7amasha).

BUT, the Slides (20-35) are self reading, INCLUDED in the exam, 2l doctor da55alhom

fel 2mte7an men 3'er ma yeshra7 3anhom.

Frequency lecture will be from last year as well, cause it was the second part of lecture 8.

Slide 18, 19: use of sensitive tests

In case of important penalty of missing a condition (dangerous but treatable

condition)

- Tuberculosis, syphilis, Hodgkin's diseaseDuring early stage of diagnostic workup with many possibilities to be considered in

order to reduce the number of those possibilities

- Fever, anemia, nauseaTo rule out diseases with a negative result of a highly sensitive test

- Highly sensitive HIV ab test early in evaluation of lung infiltrates &wt loss to rule out AIDS-related infection

When the probability of disease is very low and the purpose of test is to discover the

disease

*In summary: useful when test result is negative and we dont want false negative

results.

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Slide 20: use of specific tests

Useful to confirm a diagnosis

In cases when false positive results will harm the patient emotionally, physically and

financially

- E.g., cancer*In summary: useful when test result is positive and we dont want false positive

results

From the last year: Uses of Sensitive Tests

Clinicians should take the sensitivity and specificity of a diagnostic test intoaccount when a test is selected. A sensitive test (i.e., one that is usually positive in the

presence of disease) should be chosen when there is an important penalty for missing a

disease. This would be so, for example, when there is reason to suspect a dangerous but

treatable condition, such as tuberculosis, syphilis, or Hodgkin's disease. Sensitive tests

are also helpful during the early stages of a diagnostic workup when a great many

possibilities are being considered, in order to reduce the number of possibilities.

Diagnostic tests are used in these situations to "rule out" diseases-that is, to establish

that certain diseases are unlikely possibilities. For example, one might choose a

tuberculin skin test early in the evaluation of lung infiltrates because this test is usually

positive in people with active tuberculosis. Finally sensitive tests are useful when the

probability of disease is relatively low and the purpose of the test is to discover disease.

This is the case when the test is used to screen people without complaints, as in the

periodic health examination. In sum, a sensitive test is most helpful to the clinician

when the test result is negative.

Uses of Specific Tests

Specific tests are useful to confirm (or "rule in") a diagnosis that has been

suggested by other data. This is because a highly specific test is rarely positive in the

absence of disease-that is, it gives few false positive results. Highly specific tests are

particularly needed when false positive results can harm the patient physically,

emotionally, or financially. Thus, before patients are subjected to cancer chemotherapy,

with all its attendant risks, emotional trauma, and financial costs, tissue diagnosis is

generally required instead of relying upon less specific tests. In sum, a specific test is

most helpful when the test result is positive.

SLIDE (21-35) self reading, INCLUDED in the exam

Done by: Ammar anagreh & Bader ali (CR. Logan)