clinical approach to patients

7/28/2019 Clinical Approach to Patients

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Clinical Approach toPatients

Tanarat Choon-ngarm MD



Clinical decision making

Clinical reasoning

Use of cognitive short cuts

1. Representativeness heuristics2. Availability heuristics

3. Anchoring heuristics



Diagnostic hypothesis generation

A diagnostic hyposthesis sets a context fordiagnostic test to follow and providestestable predictions

Expert clinicians do not follow a fixedpattern in patient examination

Negative findings are often as importantas positive ones



Data collection

History

Physical examination

Investigations which depend on the

hypothesis generated from clinical findings

Interpretation of results of investigation incontext of the patient

Final diagnosis or additional investigations



Fever

Fever for one month

Fever for one month with heart murmur

Fever for one month with heart murmur

and roth spot

Provisional diagnosis : infectiveendocarditis

Essential investigations : echocardiogram,hemoculture



Dyspnea

Cardiac disease

Pulmonary disease

Metabolic causes

Psychiatric disease



Dyspnea

Acute dyspnea for one day

Acute dyspnea with bilateral wheezing

Acute dyspnea with bilateral wheezing and

cardiomegaly and third heart sound

Diagnosis : acute heart failure

Investigations : ECG and chest X-ray and

echocardiogram



Edema

Edema of both legs

Edema of both legs and ascites

Edema of both legs and ascites and

normal jugular venous pressure

Edema of both legs and ascites andnormal jugular venous pressure with

spider nevi and jaundice Diagnosis: chronic liver disease ,probable

liver cirrhosis



Approach to heart failure

What is the etiology? eg. valvular disease

Stage of heart failure? eg. stage A, B, C,or D

Functional class? eg. NYHA FC I-IV

Any precipitating factors?

Prognosis?



Alteration of consciousness

Localizing signs

No localizing signs

Diffuse brain damage from

Encephalitis

Metabolic disturbance: hyponatremiahypernatremia, hypoglycemia,

hyperglycemia, hypercalcemia, uremia,hepatic encephalopathy



Approach to neurologic patients

Locate the anatomic location of thedisease

Determine the etiology

Example: acute onset of hemiparesis withglobal aphasia indicates the location to beat the frontal and parietal lobe of thedominant hemisphere and the etiology ismost likely from vascular disease such asinfarction from thrombosis or embolism



Disease assessment

Severity or staging

Activity

Complications or sequele

Prognosis

Example : CA colon, adenocarcinoma,stage 4, complication- gut obstuction, 5

year survival 5%



Definite diagnosis

Diagnostic criteria

What investigation is the gold standard?

Example: tissue pathology is the gold

standard for the diagnosis of malignancy

A perfect diagnostic test should have asensitivity and specificity of 100%



Definition of sensitivity and specificity

Sensitivity : The fraction of those with thedisease correctly identified as positive bythe test.

Specificity: The fraction of those withoutthe disease correctly identified as negativeby the test.



Positive and negative predictive value

Positive predictive value (+ PV) is thefraction of people with positive tests whoactually have the condition.

Negative predictive value (-PV) is Thefraction of people with negative tests whoactually don't have the condition.



The sensitivity and specificity are

properties of the test.

The positive and negative predictive valuesare properties of both the test and the

population you test.

If you use a test in two populations withdifferent disease prevalence, the

predictive values will be different.

A screening test is most useful if directed to a

high-risk population (high prevalence

and high predictive value).



Calculation of sensitivity and specificity

Patient withthe disease

Patientwithout the

disease

Test ispositive

ATrue Positive

BFalse Positive

Test isnegative C

FalseNegative

DTrue Negative



Using the 2X2 table

you can calculate

Sensitivity = a / (a+c)

Specificity = d / (b+d)

+ PV = a/(a+b)

- PV = d/(c+d)

Knowing the prevalence of the diseasein the population is necessary for

these calculations



Understanding Predictive Value

Prevalence is defined as the number of patientsper 100,000 population who have the disease ata given time.

A high +PV indicates a strong chance that aperson with a positive test has the diseasewhereas a low +PV is usually found inpopulations with low prevalence of the conditionbeing examined. A high -PV means that a

negative test in effect rules out the disease.



Effects of Prevalence

Sensitivity=95% Specificity=95%

Population’s

Prevalence

0.1%

1.0%2.0%

5.0%

50%

Predictive Value of aPositive Test

1.9%

16.1%27.9%

50%

95%



Effects of Prevalence

Sensitivity=99% Specificity=99%

Population’s

Prevalence

0.1%

1.0%

2.0%

5.0%

50%

Predictive Value of aPositive Test

9.0%50%

66.9%

83.9%

99%



Test interpretation

When a sign, test or symptom has anextremely high specificity (say, over 95%), apositive result tends to rule in the diagnosis.

When a sign, test or symptom has a highsensitivity, a negative result rules out thediagnosis.

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