GP 4001 Lecture Series GP 4001 Lecture Series 2006-20072006-2007

2. Dealing with 2. Dealing with undifferentiated problems in undifferentiated problems in

primary care I primary care I

Learning Outcomes – Learning Outcomes – three principal domainsthree principal domains

• Dealing with undifferentiated Dealing with undifferentiated problems presented by patients problems presented by patients (udp)(udp)

• Management of chronic ill health Management of chronic ill health (cdm)(cdm)

• Communication Communication (comm)(comm)

Mary had a little coughMary had a little cough

Mary had a little cough

It would not go away

She went to see her GP

To see what she would say

The doctor looks and listens

And weighs up different chances

And sorts out Mary’s cough

Without the aid of medical advances

Mary’s coughMary’s cough

Mary is 36 years old Mary is 36 years old and has had her cough and has had her cough for 3 days.for 3 days.

What is the most likely What is the most likely cause of her cough?cause of her cough?

Likelihood of different Likelihood of different causes of cough of 3 causes of cough of 3

days durationdays duration

Likelihood of different Likelihood of different causes of cough of 3 causes of cough of 3

days durationdays duration

Mary’s coughMary’s cough

Mary is 36 years old Mary is 36 years old and has had her cough and has had her cough for 3 weeks.for 3 weeks.

What is the most likely What is the most likely cause of her cough?cause of her cough?

Likelihood of different Likelihood of different causes of cough of 3 causes of cough of 3

weeks durationweeks duration

Likelihood of different Likelihood of different causes of cough of 3 causes of cough of 3

weeks durationweeks duration

Mary’s coughMary’s cough

Mary is 36 years old Mary is 36 years old and has had her cough and has had her cough for 3 months.for 3 months.

What is the most likely What is the most likely cause of her cough?cause of her cough?

Likelihood of different Likelihood of different causes of cough of 3 causes of cough of 3

months durationmonths duration

Likelihood of different Likelihood of different causes of cough of 3 causes of cough of 3

months durationmonths duration

Mary’s coughMary’s cough

Mary is 36 monthsMary is 36 months(i.e. 3 years) old and has (i.e. 3 years) old and has had her cough for 3 days.had her cough for 3 days.

What is the most likely What is the most likely cause of her cough?cause of her cough?

Likelihood of different Likelihood of different causes of cough in a 3 causes of cough in a 3

year old childyear old child

Likelihood of different Likelihood of different causes of cough in a 3 causes of cough in a 3

year old childyear old child

Mary’s coughMary’s cough

Mary is 63 years old Mary is 63 years old and has had her cough and has had her cough for 3 weeks.for 3 weeks.

What is the most likely What is the most likely cause of her cough?cause of her cough?

Likelihood of different Likelihood of different causes of cough in a 63 causes of cough in a 63

year oldyear old

Likelihood of different Likelihood of different causes of cough in a 63 causes of cough in a 63

year oldyear old

Mary’s coughMary’s cough

Mary is 36 years old. She Mary is 36 years old. She works in a chicken works in a chicken factory and has had her factory and has had her cough for 3 weeks.cough for 3 weeks.

What is the most likely What is the most likely cause of her cough?cause of her cough?

Mary’s coughMary’s coughMary is 36 years old and has Mary is 36 years old and has had her cough for 3 days. had her cough for 3 days. Last week she had stomach Last week she had stomach pains. The week before she pains. The week before she had headaches. She comes to had headaches. She comes to see her doctor at least once a see her doctor at least once a week.week.

What is the most likely cause What is the most likely cause of her cough?of her cough?

What’s going on here – What’s going on here – the diagnostic processthe diagnostic process

• Cues & CluesCues & Clues• Main symptom Main symptom • AgeAge• GenderGender• DurationDuration• OccupationOccupation• Patient’s general behaviour and demeanourPatient’s general behaviour and demeanour

• Generating diagnostic ideasGenerating diagnostic ideas• Testing them using the information to Testing them using the information to

handhand

Hypothetico-deductive Hypothetico-deductive reasoningreasoning

Hypothetico-deductive Hypothetico-deductive reasoningreasoning

Cues

Information already known to doctor

Presenting information from patient

Other cues

Provisional diagnoses

Selective history and examination

Re-evaluate diagnoses

Seek confirmation by further history, examination or investigations

Diagnosis not confirmed

Diagnosis confirmed

Bayes’ TheoremBayes’ Theoremthe probability of a hypothesis being true (called the ‘posterior probability’) is a function of the probability you would have assigned to the hypothesis prior to making the observations (the ‘prior probability’) and the probabilities of the observations occurring if the hypothesis were true and the probability of the observations occurring if the hypothesis were false.

Put simply ….Put simply ….

The chances of a diagnosis being right after The chances of a diagnosis being right after we do a ‘test’ are related to the chances of we do a ‘test’ are related to the chances of the diagnosis being right before we do the the diagnosis being right before we do the ‘test’ and the chances of the ‘test’ being ‘test’ and the chances of the ‘test’ being right and the chances of the test being right and the chances of the test being wrong.wrong.

N.B. All history, examination, investigation N.B. All history, examination, investigation and information about a patient functions and information about a patient functions effectively as a ‘test’ in this context.effectively as a ‘test’ in this context.

Shifting probabilities and Mary’s Shifting probabilities and Mary’s

cough –cough – Bayes’ Theorem in actionBayes’ Theorem in action

InformationInformation Likelihood of lung Likelihood of lung cancercancer

Mary has a coughMary has a cough Very lowVery low

Mary is 63 years oldMary is 63 years old Still quite lowStill quite low

She has smoked 20 a She has smoked 20 a day all her adult lifeday all her adult life

A bit higherA bit higher

She has coughed up She has coughed up blood and has lost blood and has lost

weightweight

Quite highQuite high

(ought to refer)(ought to refer)

Here comes the science Here comes the science bit!bit!

Characteristics of tests – Characteristics of tests – Sensitivity and SpecificitySensitivity and Specificity

• Sensitivity of a test is the Sensitivity of a test is the proportion of patients who test proportion of patients who test positive for the disease who positive for the disease who actually have the diseaseactually have the disease

• Specificity of a test is the Specificity of a test is the proportion of the patients who test proportion of the patients who test negative for the disease who negative for the disease who actually do not have the diseaseactually do not have the disease

Sensitivity and Sensitivity and SpecificitySpecificity

  

TARGET DISORDERTARGET DISORDER

  PRESENTPRESENT ABSENTABSENT

DIAG-DIAG-NOSTIC NOSTIC

TEST TEST RESULTRESULT

++ aa bb a + ba + b

-- cc dd c + dc + d

   a + ca + c b + db + d a + b + c + da + b + c + d

Sensitivity = a/(a+c) Specificity Sensitivity = a/(a+c) Specificity = (d/b+d)= (d/b+d)