'DAMN-IT' acronym offers practical diagnostic aid

Most would agree that a correct diagnosis is an essential prerequisite to providing safe and effective treatment for various illnesses.

Diagnosis of specific causes of various clinical disorders is of importance because it facilitates: 1) accurate forecasts (e.g. prognosis) of the biological behavior of the disorder, and, 2) selection of specific (rather than symptomatic or supportive) therapy for the disorder. However, diagnoses are often a matter of opinion rather than matter of fact. In fact, isn't it true that most diagnoses often require us to make decisions in the absence of certainty?

Our diagnoses are based on probability. This being the case, we must use caution not to fall into the trap of making diagnoses on the basis of faulty logic or insufficient information. 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.

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, short cuts are often 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. A misdiagnosis can be more detrimental to the patient than the illness. A wise sage penned this thought: "Heaven defend me from a busy doctor."

Recall that the problem-oriented veterinary medical system is a simple, structured and reproducible set rules and directions that efficiently and effectively guide our care of patients. It is based on four related phases of medical action: 1) initial collection of information (so-called database); 2) identification of problems (so-called problem list; 3) devising plans to further refine the causes of problems, and also devising plans to treat the problems (so-called initial plans); and, 4) interpretation and recording of additional information generated by initial plans in order to determine whether additional diagnostic and/or therapeutic plans are necessary (so-called follow-up plans; also called progress notes).

A frequent error in diagnostic reasoning, made even by veterinarians with years of experience, is prematurely guessing the specific cause of an illness, first, without 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. Making a practice of bypassing the fundamental priorities of diagnostic planning often results in over dependence on past experiences or textbook descriptions to identify the underlying causes of various diseases. As a result, our ability to recognize specific causes of diseases that we have not encountered previously is hindered. Likewise, memorization of textbook descriptions of characteristic clinical findings of specific diseases is not consistently effective. Why not? In different patients, the same disease typically induces a variety of manifestations of different degrees of severity. Most textbook descriptions are compilations of prototypical manifestations of diseases, all of which do not coexist in the same patient. Just as no two individuals are exactly alike in health, so neither are any two alike in disease.

Based on the premise that a well-defined problem is half solved, the primary objective of this Diagnote is to review application of the DAMN-IT acronym as an aid in formulation of diagnostic plans (a component of the third phase of medical action of the problem oriented system).

Priority plans

To enhance our ability to detect the underlying cause of various types of illness, we chronologically follow a prioritized sequence of diagnostic steps (Table 1, Osborne: Veterinary Clinics of North America, Vol. 13, Nov. 1983). To summarize, after initial identification of the patient's problems (Phase 1- Database) and appropriate refinement of these problems (Phase 2-Problem List), further diagnostic plans are formulated to confirm and identify the underlying causes of these problems (Phase 3-Initial problem list). When formulating diagnostic plans, we routinely follow the following 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 mechanism(s)

associated with the identified problems (DAMN-IT acronym; Table 2), and 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

.

Table 1: Four phases of medical action

The acronym

The DAMN-IT acronym encompasses familiar pathophysiologic disease processes. Therefore, with routine use, it rapidly becomes part of our memory. When routinely used in conjunction with the history, physical examination and other diagnostic data, the acronym facilitates rapid and reproducible formulation of probable rule outs (or tentative diagnoses) for each of the patient's undiagnosed problems. Since I developed the DAMN-IT acronym as an aid to taking examinations when I was a sophomore veterinary student in 1962, I have added some additional pathophysiologic mechanisms (Table 2). 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; and developmental, anomalous, and inherited).

Table 2: DAMN-IT acronym of pathophysiologic causes of disease

What is next?

After developing a list of pathophysiologic mechanisms likely to be causing the clinical problems, the most probable cause(s) of these problem(s) 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, are dependent on several factors, especially the status of the patient.

If rapidly changing problems are likely to result in irreversible dysfunction or if the problems are an immediate threat to the patient's life, then diagnostic plans for several rule-outs should be implemented simultaneously (that is, in parallel).

For example, if a critically-ill patient is admitted because of rapidly progressing vomiting, dehydration, impaired urine concentrating capacity and extreme depression, it is advisable to simultaneously implement diagnostic plans to rule-out renal failure, diabetic ketoacidosis, hypoadrenocorticism, pyometra and hepatic dysfunction. If an individual priority list of these rule-outs is established and plans are implemented to rule-out only one cause at a time (that is, in series), then the patient might die before a specific diagnosis is established.

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 on the basis of 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.

The Greek term " iatros" means physician and is derived from the word "iasthai", which means to heal or cure. In the context of pathophysiologic mechanisms of disease, what is the significance of the term iatrogenic (Table 2)? The term iatrogenic means "physician induced". The fact that the term iatrogenic is listed as a pathophysiologic mechanism of disease emphasizes that there are some patients we cannot help, but there are none we cannot harm.

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.