Clinical Reasoning in Veterinary Practice. Группа авторов
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the lesion.
Once the location of a problem within a body system is determined, usually the next key question is, What is it? You need to identify the pathology – define the lesion. This is now your differential list. It can be helpful to remember the types of pathology that can occur in broad terms – for example, degeneration, anomaly, metabolic, neoplasia, nutritional, infection, inflammation, idiopathic (‘genetic’), trauma, toxic and vascular (DAMNIT‐V).
Which type of pathology is most likely going to depend on the body system or organ involved, the signalment of the patient (species, breed, age, sex etc.), the clinical onset and course of the clinical signs, the geographic location of the patient and what disorders are common in that population.
This assessment can be influenced by whether the patient is in a general clinic or a referral hospital. Common things occur commonly or ‘the hoof beats in the night are much more likely to be due to a horse than a zebra’ (unless you are on safari, of course!). This doesn’t mean that uncommon diagnoses should not be considered (and they will of course be more common in specialist hospitals). It’s just that common disorders usually receive diagnostic priority at the beginning of a clinical investigation in general practice.
Example: the patient has a gastric lesion – is it a tumour, foreign body or ulcer?
This question will require visualisation and/or biopsy to answer, but it would have been a waste of time asking the question until you had arrived at the right location.
Other examples include the following:
Spinal cord pathology identified based on a neurological examination – is it inflammation, infection or a neoplasm?
Haematuria is due to lower urinary tract disease – infection, calculi or neoplasia?
Large bowel diarrhoea – parasites, infection, ulceration, stricture, neoplasia or diet related?
Putting it all together
What do I need to do to define the problem, system, location or lesion?
The diagnostic methods used to define the problem, the system, where appropriate the anatomical location and the lesion will vary depending on the problem.For example, clinical pathology may be needed in some cases to define the problem (e.g. is red urine due to blood or haemoglobin?), but in many cases, the problem will be definable on the basis of history (onset and course of the disease) and clinical examination findings.
Similarly, diagnostic tests or procedures may be required to define and refine the body system involved in some cases, and for other problems, the system involved will be evident from clues from the history and/or the clinical examination.
In some cases, once the problem is defined, for example, regurgitation, the body system is immediately apparent and the anatomical location identified (upper GI tract – oesophagus or pharynx).
For neurological problems, clinical and neurological examination will often define the problem, system and location, leaving only the lesion needing to be defined by diagnostic testing.
Are the steps always in the same order?
The order in which the problem, system, location and lesion are defined may change for some problems.
For example, when assessing coughing and diarrhoea, identifying the location occurs before identifying the system, as location identification helps identify the system (discussed in more detail in Chapters 4 and 9).
For some problems, for example, pruritus (Chapter 15), you might go straight from problem definition to seeking to define the lesion.
However, for almost all clinical problems, answering some or all of the four questions – What is the problem? What system is involved and how? What is the location of the lesion? and What is the lesion? – will provide a framework to guide your clinical reasoning and diagnostic and therapeutic decisions.
Thus, instead of thinking when faced with a vomiting patient, ‘I wonder if it has a gastric foreign body or renal failure or a liver tumour?’, your initial energies are directed at defining the problem and system, which will help make your list of differentials (which are usually the location and/or lesion) logical, appropriate and given appropriate priority. In this way, the diagnosis is made thoughtfully, and during the process, all diagnostic options can be considered as the need arises.
But does pattern recognition have a place?
It is important to reiterate that pattern recognition for many cases is appropriate and justified – depending on your level of experience, knowledge, skill base and mindset. For example, if a pot‐bellied elderly terrier with bilaterally symmetrical alopecia, hyperpigmentation and comedones walked into your consulting room and the owner reported that the dog was drinking lots of water, was ravenously hungry and appeared to be panting excessively, then hyperadrenocorticism is the most obvious diagnosis, and going through the motions of assessing each specific problem would be ridiculous (but not if you had never seen a dog with hyperadrenocorticism before!).
However, it is important to be aware that pattern recognition is only foolproof if:
The pattern is virtually unique to the disease
You consider a sufficient number of factors in your pattern
You carefully evaluate that your pattern does explain all of the clinical problems (and don’t ignore those that don’t)
Or there are a very limited number of diagnostic options.
The value and effectiveness of pattern recognition is very dependent on the clinician’s experience, depth of knowledge, understanding and ability to sort data quickly and efficiently.
Of course, once you have considered each individual problem, you do in fact look for a pattern in the clinical signs. However, the insertion of that initial step of considering each specific problem individually and then relating it to the other problems present should ensure that you don’t miss the less obvious possible diagnoses.
In addition, the process of developing a sound problem‐based approach can enhance your ability to pattern recognise because you have a greater understanding of the reasons why you believe certain patterns are suggestive of some disorders more than others.
Combinations of clinical signs
There are some combinations/patterns of clinical signs that make the diagnostic options very limited, and it is entirely appropriate to consider them together; for example, the patient with PU/PD who is also polyphagic. If the PU/PD and polyphagia have been present for the same length of time, then they are almost certainly due to the same disorder, and it is quite appropriate to assess them together. There are very few conditions that will cause this pattern of clinical signs (e.g. diabetes mellitus, hyperthyroidism and hyperadrenocorticism), so it is quite appropriate to concentrate on these first.
Does this make sense?
Always ask yourself, particularly when assessing clinical pathology or results of other diagnostic procedures in light of particular problems, Does this make sense – does this clinicopathological abnormality explain the problem that the animal has? Good clinicians are good detectives!
Example 1
A dog is depressed, anorectic, vomiting and polydipsic.
Its