1. Introduction
How should we conceive of and evaluate the process of medical diagnosis?
Saying that it is a matter of inferring the correct disease from the
available signs and symptoms is too sparse. Clinical diagnosis is anexperimental science based on observation, hypotheses, and
testing. It is a dynamic process that involves observation, diagnostic
conjectures and testing, possibly leading to new or revised conjectures.
For the clinician, it should always be a reflexive process subject to
revision.
Consider for example the following scenario: A 54-year-old man with no
previous history of chronic disease suffers sudden substernal chest pain
and is rushed to an emergency room. His presenting symptoms also include
tachycardia (abnormally rapid heart rate), shortness of breath and
sweating. The challenge a clinician faces in cases like this is not just
to evaluate the likelihood of different possible causes of these
symptoms; she also has to select which hypotheses to actively consider
in the first place, which to prioritize for further testing, which can
be put aside for the time being and when to initiate treatment on the
basis of a given hypothesis. Additionally, all of these decisions
presuppose that the relevant hypotheses have been generated and
introduced into the diagnostic inquiry. The clinician does not start out
considering every possible cause of chest pain known to medicine;
rather, she needs to decide when and how to generate new diagnostic
hypotheses, as well as when to stop.
In this paper, we present a framework for understanding the different
kinds of reasoning underlying medical diagnosis as it occurs in clinical
practice. Our starting point is the observation that, in addition to
evaluating the likelihood of candidate diagnostic hypotheses in light of
the evidence, the process of medical diagnosis involves two distinct
types of reasoning, namely: (i) reasoning concerned with generating new
candidate hypotheses and (ii) reasoning about which hypotheses should be
pursued, i.e. prioritized for testing and further consideration. That
these forms of reasoning are crucial to understanding inquiry was argued
by C. S. Peirce in his writings on the form of reasoning he calledabduction . Following recent commentators (Upshur 1997; Stanley
and Campos 2013, 2015; Chiffi and Zanotti 2015), we believe that
Peirce’s mature account of abduction provides important lessons for
understanding diagnostic reasoning. Specifically, we argue that recent
Peirce scholarship, which construes abduction in terms ofstrategic reasoning , provides a promising framework for analyzing
diagnostic reasoning.
Our aims in presenting this framework are primarily normative: we want
to explicate the reasons which underlie diagnostic reasoning in
realistic clinical situations, rather than necessarily describing the
psychological processes clinicians go through in diagnosis. The best
psychological description may often be that the clinician makes a quick,
intuitive judgment, perhaps based on some unconscious heuristic. By
contrast, our framework aims to explicate the factors which make such
judgments reasonable in a concrete, clinical situation. Despite this
normative scope, our aims in this paper are not prescriptive in the
sense of recommending whether existing practices can or should be
improved. Rather, our main aim is to be able to explicate diagnostic
reasoning as it occurs in current practice.
A unified, normative framework for understanding clinical reasoning is
currently lacking from the methodological literature. On the one hand,
when hypothesis generation is addressed (e.g. Kassirer, Wong and
Kopelman 2010, Ch. 13) it is mainly discussed from the perspective of
cognitive psychology without an underlying normative framework. On the
other hand, the probabilistic approach to clinical-decision-making
currently popular in the medical literature—the so-calledthreshold approach —while normative, does not address the
question of hypothesis generation. As we shall argue, because of the way
hypothesis generation and reasoning about pursuit are intertwined, this
neglect means that threshold models, in their current form, fail to
capture all relevant reasons for pursuing a hypothesis.
Our discussion proceeds as follows. We start, in Section 2, by outlining
our understanding of Peircean abduction and, Section 3, explaining how
these ideas apply to medical diagnosis. In Section 4, we then use this
framework to analyze a clinical case study. In Section 5 we return to
our criticism of threshold models. Finally, in Section 6, we defend the
strategic reasoning interpretation of abduction as a framework for
analyzing diagnostic reasoning.