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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)
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)