Generating and Selecting Diagnostic Hypotheses
Donald E. Stanley, Maine Medical Center, Department of Pathology,
Portland, Maine.
Rune Nyrup, Durham University, Department of Philosophy
Francis Bacon: ‘shake out the folds of nature’ ‘twist the
lion’s tail’
Charles Darwin: “ I think that I have become a little more skillful in
guessing right explanations and in devising experimental tests; but this
may probably be the result of mere practice, and of a large store of
knowledge.”
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Introduction:
Clinical diagnostic medicine is an experimental science based on
observation, hypotheses, and testing. It is a dynamic process that
involves skills in history taking, observation, diagnostic conjectures
and testing, possibly leading to new or revised conjectures. For the
clinician, it is always a reflexive process subject to revision. In this
article, we want to provide experiential insight into the logic of this
diagnostic process.
Our aim is to describe the logic of medical diagnosis as it is practiced
in clinical medicine recognizing the pragmatics of diagnosis. We
primarily aim to describe (rather than prescribe) the structures and
patterns of reasoning used by experienced clinicians under different
diagnostic circumstances and how these patterns of inquiry allow further
insight into the evaluation and proposed treatment of patients. We
however start by introducing a general account of the logic of medical
diagnosis in order to focus our analysis of a detailed clinical case. So
first things first . . .
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The Logic of Medical Diagnosis
The process of diagnosis consists of three types of reasoning: (1)
generation of a plausible diagnostic hypotheses, or abduction; (2)
selection and prioritization of hypotheses for further testing; (3)
acceptance or rejection of diagnoses. Although these are in practice
often overlapping or intertwining processes, they can be distinguished
logically.
The first type refers to the process of eliminating implausible
diagnoses and generating plausible diagnoses after observing and
considering a patient’s previous history, presenting condition, signs,
and symptoms. The diagnostic process begins with an abductive
search for the differential diagnosis. Charles Peirce observed that this
process has a logical form, namely:
The surprising fact, C, is observed.