The "DAMN IT" acronym: Are you using this practical diagnostic aid?

Editor's note: This is an update from an article that first appeared in the March 2005 issue of DVM Newsmagazine.

Most veterinarians would agree that a correct diagnosis is an essential prerequisite to consistently providing safe and effective treatment for various illnesses. Diagnosing specific causes of disorders is of clinical importance since it facilitates accurate forecasts (e.g., prognosis) of the biologic behavior of the disorder and selection of the type (e.g., specific, supportive, symptomatic or palliative) of therapy for the disorder.

However, diagnoses are often a matter of opinion rather than a matter of fact. After all, isn't it true that most diagnoses often require us to make decisions in the absence of certainty?

Rather, our diagnoses are based on probability. Since this is the case, we must be careful not to fall into the trap of making diagnoses based on faulty logic or insufficient information. It's one thing to make a diagnosis and another to be able to substantiate it. Although we name the things we know, we don't necessarily know them because we name them. This axiom certainly applies to diagnoses.

Shortcuts in diagnostic reasoning tend to become increasingly prevalent when we veterinarians are subjected to the pressures of a high caseload in a busy hospital. In this context, shortcuts often are defended based on practicality. Although practicality is a virtue, we must not use the concept of practicality as an excuse for ignorance. Why? Because, taking shortcuts that result in a misdiagnosis ultimately may be more detrimental to the patient than the illness. A wise sage once penned: "Heaven defend me from a busy doctor."

Diagnostic pitfalls

Recall that the problem-oriented veterinary medical system is a conceptually straightforward, structured and reproducible set of rules and directions that efficiently and effectively guide our care of patients. It's based on four related phases of medical action:

1. Initially collecting information (i.e., database)

2. Identifying problems (i.e., problem list)

3. Devising plans to further refine the causes of problems and to treat the problems (i.e., initial plans)

4. Interpreting and recording additional information generated by initial plans to determine if additional diagnostic or therapeutic plans are necessary (i.e., follow-up plans or progress notes).

A frequent error in diagnostic reasoning, even made by veterinarians with years of experience, is prematurely guessing the specific cause of an illness without, first, verifying the presence of the problems (especially problems identified by owners); second, localizing problems to various organs or body systems; or third, considering basic pathophysiologic disease mechanisms that might be involved.

Bypassing the fundamental priorities of diagnostic planning often results in overdependence on past experiences or textbook descriptions to identify the underlying causes of disease. As a result, our ability to recognize specific causes of diseases that we have not previously encountered is hindered.

Likewise, memorizing textbook descriptions of characteristic clinical findings of specific diseases is not consistently effective. Why? Because, in different patients, the same disease typically induces various manifestations of different degrees of severity. Most textbook descriptions are compilations of prototypical disease manifestations, all of which don't coexist in the same patient. Why is this generality important? Because, just as no two individuals are exactly alike in health, so are there no two alike in disease.

Based on the premise that a well-defined problem is half-solved, the primary objective here is to summarize application of the "DAMN IT" acronym (Table 1) as an aid formulating diagnostic plans (a component of the third phase of medical action of the problem-oriented system).

TABLE 1 DAMN IT acronym of pathophysiologic causes of disease

Priority of diagnostic plans

Where does the DAMN IT acronym fit into the diagnostic process? When formulating diagnostic plans, we routinely follow this sequence of steps:

1. Verify or confirm the presence of problems, especially those defined by clients.

2. Localize problems to an organ or body system.

3. Consider the most probable pathophysiologic mechanisms associated with the identified problems (DAMN IT acronym; Table 1).

4. Based on the probable (in contrast to the possible) pathophysiologic mechanisms present in the patient, formulate specific diagnostic rule-outs (tentative diagnoses) that would explain the underlying cause of the problems, and implement diagnostic tests to confirm them.

By using the DAMN IT acronym when considering diagnostic rule-outs, numerous diagnostic possibilities can be logically reduced to a few diagnostic probabilities.

The DAMN IT acronym

Each letter in the acronym represents one or more pathophysiologic disease processes. Examine Table 1 and begin with the letter "D," which may stimulate your recall of pathophysiologic mechanisms such as degenerative osteoarthritis or degenerative aging to explain severe lameness localized to both coxofemoral joints of a 10-year-old German shepherd. The letter "D" may also stimulate your recall of developmental or congenital disorders, such as glomerulonephropathy to explain unthriftyness, progressive azotemia, severe proteinuria, isosthenuria, etc., in an English cocker spaniel.

The letter "M" could prompt one to think of a metabolic disorder, such as diabetes mellitus to explain progressive vomiting, marked dehydration, impaired urine concentrating capacity and extreme depression.

If we routinely use it, the DAMN IT acronym rapidly becomes part of our memory. When used in conjunction with the history, physical examination and other diagnostic data, the acronym facilitates rapid and reproducible formulation of probable rule-outs (i.e., as tentative diagnoses) for each of a patient's undiagnosed problems. In 1962 when I was a sophomore veterinary student, I created the DAMN IT acronym as an aid to taking examinations. I have added a few pathophysiologic mechanisms since that time (Table 1). As an iterative memory aid, some of the pathophysiologic mechanisms listed with different letters in the DAMN IT acronym overlap (i.e., autoimmune and immune; developmental, anomalous and inherited).

What is next?

After developing a list of pathophysiologic mechanisms likely to be causing the clinical problems, the most probable causes of these problems should be ruled in or ruled out by implementing appropriate diagnostic plans. The specific diagnostic tests and procedures chosen to evaluate each problem, and the rate and frequency with which these tests are implemented, depend on several factors, especially the patient's status.

If a patient is admitted with an acute onset of rapidly changing problems that are assessed to be an immediate threat to life, diagnostic plans for several rule-outs should be implemented simultaneously. For example, if a critically ill patient is admitted because of rapidly progressing vomiting, dehydration, impaired urine concentrating capacity and extreme depression, it's advisable to simultaneously implement diagnostic plans to rule out renal failure, diabetic ketoacidosis, hypoadrenocorticism, pyometra, hepatic dysfunction and systemic toxicity.

If a priority list of investigation is established so you don't evaluate the second rule-out until the first rule-out has been eliminated, and follow-up plans are implemented to rule out only one problem at a time (i.e., in series), the patient may die before a specific diagnosis is established. In contrast, if a patient has had intermittent progressive urinary incontinence for the past seven months, one can initially justify a less comprehensive diagnostic approach associated with the expenditure of less duplication of resources.

Concluding caveats

Diagnoses should not be overstated by guessing their underlying cause based on insufficient evidence. They should be stated at the level of refinement that can be reasonably justified based on current knowledge about the patient. Why? Because if the diagnosis is overstated, then misdiagnosis, misprognosis and formulation of ineffective or contraindicated therapy can result. No patient should be worse for having seen the doctor.

Dr. Osborne, a diplomate of the American College of Veterinary Internal Medicine, is professor of medicine in the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota.