10 axioms to aid your diagnostic skills - DVM
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10 axioms to aid your diagnostic skills


DVM360 MAGAZINE


AXIOM 1: Clinical impressions are inherently unreliable, generally conforming to our preconceived biases.

Strong preconceptions are not a substitute for objective evidence. For example, on the basis of logic, urologists have for decades instructed human patients with calcium oxalate uroliths to reduce their dietary calcium intake to minimize stone recurrence. However, several contemporary epidemiological studies have revealed that reducing dietary calcium actually increased the frequency of calcium oxalate urolith recurrence. What is the point? Belief or skepticism does not alter the truth. Rather than forcing preconceived conclusions on the facts, we must be alert to allow reproducible observations (facts) to lead us to reasonable conclusions.

AXIOM 2: There is a difference between problem definition and problem solution.

We use the term diagnosis in context of defining the cause(s) of clinical signs. The ability to define a patient's medical problems without overstating them is a crucial first step in the diagnostic process, since one must be able to accurately define problems before they can be solved. No veterinarian has or ever will be trained to single-handedly solve all types of medical problems. No one can recall enough knowledge and be proficient with enough techniques to guarantee that (s)he alone can provide the best care of very patient. Veterinarians can be trained to accurately identify problems, however. They can and should be master "problem definers." Accurate definition of a patient's clinical problems will permit us in our role as diagnosticians to more efficiently utilize available resources, such as journals, books, the internet, consultations, and referrals, to help resolve diagnostic problems. A problem well defined is half solved!

AXIOM 3: There is a conceptual difference between observations and interpretations. Discernment of the difference between observations and interpretations of them (inferences) is critical to making a diagnosis.

Clients frequently confuse these two types of information when describing the illness of their animals to us. A classic example is to misinterpret the observation of tenesmus as constipation in a male cat with urethral obstruction. Although either observations or interpretations may be erroneous, in my experience misinterpretation of a correct observation is the most common pattern of error. A misinterpreted problem is the worst of all problems. Why? Because if erroneous interpretations are accepted as facts, erroneous diagnosis followed by erroneous prognosis and formulation of ineffective or contraindicated therapy may result. This is indeed ironic, in that the patient may acquire a worse condition as a result of having visited the doctor (e.g., the concept of iatrogenesis).

AXIOM 4: There is a difference between disease-induced clinical signs and clinical signs associated with the body's homeostastic compensatory response to disease-induced clinical signs.

Clinical manifestations of disease can be subdivided into the following two classes:

1) signs directly induced by the disease (such as impaired urine concentrating capacity and obligatory polyuria associated with damage to the countercurrent system in patients with bilateral bacterial pyleonephritis), and

2) the body's compensatory response to these signs (such as compensatory polydipsia to maintain fluid balance despite obligatory persistent polyuria).

Other examples of this relationship include compensatory inflammation in response to damaged tissue, fever in response to systemic infectious agents, polychromasia and reticulocytosis in response to anemia and hyperparathomonemia in response to hypocalcemia. Logically then, making a diagnosis of urinary-tract infection solely on the basis of pyuria would be an over-diagnosis because pyuria may be a compensatory response to infectious or noninfectious diseases of the urinary tract.

AXIOM 5: There is a conceptual difference between disease and failure.

Discernment of the conceptual difference between organ disease and organ failure also is fundamental to proper diagnostic refinement. Organ function that is "adequate " to sustain homeostasis is usually not synonymous with "total " organ function. For example, patients with only one functional kidney (an organ donor) have adequate renal function to live a "normal " life without manifestations of renal dysfunction. Even when slowly progressive irreversible renal lesions occur, signs of organ dysfunction do not develop as long as adequate quantities of functional parenchyma (i.e., nephrons) remain to maintain homeostasis. This concept is the basis for distinguishing organ disease (such as cardiac valvular insufficiency associated with normal pulse rate and rhythm) from organ failure (such as abnormal circulation associated with abnormal cardiac rate and rhythm which ultimately occur as a result of irreversible progressive cardiac valvular insufficiency). The approach to management of a patient with cardiac valvular insufficiency and adequate cardiac function is very different from management designed for a patient with cardiac valvular insufficiency and congestive heart failure.


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Source: DVM360 MAGAZINE,
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