Diagnostic Axioms
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Treating a patient without a diagnosis is analogous to shooting without aiming.
Body systems and organs manifest the effects of a variety of different causes of disease in a limited number of ways (pruritis,
alopecia, vomiting, diarrhea, polyuria, polydipsia, seizures, coma, azotemia, anemia, etc.). All of these clinical signs may
have different causes that are not always easy to distinguish by routine clinical procedures. The ability to reliably and
consistently establish the different causes of various types of illness requires specialized knowledge, and the wisdom to
wisely apply that knowledge in such fashion that it will benefit patients.
The noun "diagnosis" is derived from a Greek word meaning to distinguish or discern. The word "discern" conveys the concept
of an ability to recognize and understand the difference between two or more things. In this context, it is one thing to make
a diagnosis, and another to be able to substantiate it.
Though we name the things we know, we do not necessarily know them because we name them. If we begin the diagnostic process
with a preconceived notion (or bias) about the cause of a patient's illness, we have a tendency to ask questions and perform
diagnostic procedures to support our preconceptions. We tend to ignore clinical findings that do not fit our stereotype.
If we are not careful in how we collect information, we may derive erroneous diagnoses. In fact, an erroneous diagnosis is
one of the most common diseases.
Would you agree that a correct diagnosis is a key prerequisite to providing safe and effective treatment for various illnesses?
Would you also agree that diagnoses often are a matter of opinion rather than matter of fact? Isn't it true that most diagnoses
often require us to make decisions in the absence of certainty?
Medical diagnoses are based on probability. Therefore we must use caution not to fall into the trap of making them on the
basis of faulty logic or insufficient information.
Shortcuts in diagnostic reasoning tend to become increasingly prevalent when veterinarians are subjected to the pressures
of a high caseload in a busy hospital. In this context, shortcuts often are defended on the basis of practicality. Although
practicality is a virtue, we must use caution not to use the concept of practicality as an excuse for ignorance. Why? Because,
a misdiagnosis may be more detrimental to the patient than the illness. A wise sage once penned this thought: "Heaven defend
me from a busy doctor."
How do we know when our diagnoses are in error? If we do not have a system designed to periodically audit our diagnoses for
accuracy, we are less likely to recognize and correct our errors. If the accuracy of our diagnoses is never questioned, we
may become over-confident in our judgments with a tendency to rely less and less on clinical data and more and more on our
intuition. What is the inevitable result? Experience has revealed that diagnosis by intuition is often a rapid method of reaching
the wrong conclusion.
Based on the premise that almost right is still wrong, the primary objective of this diagnote is to review some clinical axioms
that foster the diagnostic process.
Diagnostic axioms
After 45 years of serving as a clinician in a university hospital, I have learned that periodically reviewing diagnostic axioms
is helpful as a self-teaching aid. An "axiom" is a statement universally accepted as true. In the box (p. 10S), I have listed
10 key axioms associated with the diagnostic process. Review the items and test yourself as to whether you can explain (or
define) them. Then review the explanations.
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