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Oxford Handbook of Clinical Diagnosis



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Author: Huw Llewelyn and Hock Aun Ang

Publisher: Oxford University Press

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Publish Date: November 18, 2014

ISBN-10: 019967986X

Pages: 704

File Type: PDF

Language: English

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Book Preface

Last year, I celebrated my 30th year as a doctor and my son began his training as a (graduate entry) medical student. I have come to enjoy the intergenerational ‘grand rounds’ in which one of us describes a case in the time-honoured format—starting with a structured history, going on to the clinical examination and adding diagnostic tests that progress from the simple and non-invasive to all the wonders and dreads of modern technology—while the other tries to guess the diagnosis from as few clues as possible. Given that most medical knowledge now lies in the category ‘forgotten by the mother and not yet encountered by the son’, this book is likely to become well thumbed by both of us as we play our diagnostic game.

Much of this book reflects the fact that Huw Llewelyn is a mathematician and logician as well as a highly experienced physician. In many cases, diagnosis can and should be a process of deduction that begins with a ‘diagnostic lead’ (a single symptom or sign, such as ‘right iliac fossa pain’, that gets you started), the cause of which can be progressively narrowed and refined by incorporating factors such as age and gender; the timing and speed of onset; the pattern of associated symptoms, signs and pre-existing conditions; and the results of investigations. Frontal headache in a teenager who was well until yesterday is likely to have a different cause from frontal headache that has been present for many months in a 65-year-old with hypertension and depression. Evidence can often be collected in the history and clinical examination that is ‘suggestive’ or ‘confirmatory’ (use these terms with care—they are defined in the book) of particular diagnostic possibilities. More rarely, certain tests or combinations of tests can effectively ‘rule in’ or ‘rule out’ certain diagnostic options.

You probably knew all that already, so what will you learn from this book that goes beyond standard teaching on clinical diagnosis? For me, the added value was in the sophistication with which the principles of probability and decision science have been applied to the many and varied challenges of clinical practice. The book’s (mainly implicit) message is that if you take a logical and step-wise approach, using your experience, history-taking skills, and clinical acumen to select the best diagnostic leads and add granularity to your decision tree, you will often render costly and unpleasant diagnostic tests redundant. Less commonly, you will justify the expense and inconvenience of such tests in selected patients.

The skilled diagnostician is not the one who rattles off a long list of differential diagnoses for every symptom, applies algorithms mechanically, ticks all the boxes on a blood request form or scans the head of every patient with blurred vision. Rather, the skilled diagnostician is the one who combines thoughtful history-taking, focused clinical examination, and judicious investigation so that each successive step contributes to an emerging picture of the problem and informs the selection of the next step. As the authors say (p.20), ‘It is important to understand that clinical diagnosis is not a static classification system based on diagnostic criteria or their probable presence. It is a dynamic process.’ Last year, I celebrated my 30th year as a doctor and my son began his training as a (graduate entry) medical student. I have come to enjoy the intergenerational ‘grand rounds’ in which one of us describes a case in the time-honoured format—starting with a structured history, going on to the clinical examination and adding diagnostic tests that progress from the simple and non-invasive to all the wonders and dreads of modern technology—while the other tries to guess the diagnosis from as few clues as possible. Given that most medical knowledge now lies in the category ‘forgotten by the mother and not yet encountered by the son’, this book is likely to become well thumbed by both of us as we play our diagnostic game.

Much of this book reflects the fact that Huw Llewelyn is a mathematician and logician as well as a highly experienced physician. In many cases, diagnosis can and should be a process of deduction that begins with a ‘diagnostic lead’ (a single symptom or sign, such as ‘right iliac fossa pain’, that gets you started), the cause of which can be progressively narrowed and refined by incorporating factors such as age and gender; the timing and speed of onset; the pattern of associated symptoms, signs and pre-existing conditions; and the results of investigations. Frontal headache in a teenager who was well until yesterday is likely to have a different cause from frontal headache that has been present for many months in a 65-year-old with hypertension and depression. Evidence can often be collected in the history and clinical examination that is ‘suggestive’ or ‘confirmatory’ (use these terms with care—they are defined in the book) of particular diagnostic possibilities. More rarely, certain tests or combinations of tests can effectively ‘rule in’ or ‘rule out’ certain diagnostic options.

You probably knew all that already, so what will you learn from this book that goes beyond standard teaching on clinical diagnosis? For me, the added value was in the sophistication with which the principles of probability and decision science have been applied to the many and varied challenges of clinical practice. The book’s (mainly implicit) message is that if you take a logical and step-wise approach, using your experience, history-taking skills, and clinical acumen to select the best diagnostic leads and add granularity to your decision tree, you will often render costly and unpleasant diagnostic tests redundant. Less commonly, you will justify the expense and inconvenience of such tests in selected patients.

The skilled diagnostician is not the one who rattles off a long list of differential diagnoses for every symptom, applies algorithms mechanically, ticks all the boxes on a blood request form or scans the head of every patient with blurred vision. Rather, the skilled diagnostician is the one who combines thoughtful history-taking, focused clinical examination, and judicious investigation so that each successive step contributes to an emerging picture of the problem and informs the selection of the next step. As the authors say (p.20), ‘It is important to understand that clinical diagnosis is not a static classification system based on diagnostic criteria or their probable presence. It is a dynamic process.’


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