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specific clinical signs that give the clinician a ‘diagnostic hook’ he/she can use as a basis for the case assessment.
As the clinician increases understanding of the clinical status of the patient, the overall aim is to seek information that allows them to define each problem more specifically (i.e. narrow down the diagnostic options) until a specific diagnosis is reached.
For example, for Erroll the prioritised problem list would be:
1 Vomiting
2 Dysuria and haematuria
3 Anorexia
4 Depression.
This is because vomiting and dysuria/haematuria are specific problems, and their assessment will hopefully assist in reaching a diagnosis – they are our ‘diagnostic hooks’. Anorexia and depression will be explained by the underlying disorder and are important to note but are not ‘diagnostic hooks’ for this case – they are the ‘background information’.
Specificity is relative!
The relative specificity of a problem will, however, vary depending on the context.
For example, for a dog that presents with intermittent vomiting and lethargy, vomiting is the most specific problem, as in all likelihood the cause or consequences of the vomiting will also explain the lethargy.
In contrast, for the dog that presents with intermittent vomiting and lethargy and is found to be jaundiced on physical examination, jaundice is the most specific clinical problem. This is because:The majority of causes of jaundice can also cause vomiting, but the reverse is not true, that is, there are many causes of vomiting that do not cause jaundice.Thus, there is little value in assessing the vomiting as the ‘diagnostic hook’, as it will mean that many unlikely diagnoses are considered, and time and diagnostic resources may be wasted.
In this case, assessment of jaundice will lead more quickly to a diagnosis than that of vomiting, as the diagnostic options for jaundice are more limited than those for vomiting.
In other words, although you identify and consider each problem to a certain degree, you try to focus your diagnostic or therapeutic plans on the most specific problem/s (the ‘diagnostic hook/s’) if (and this is important) you are comfortable that the other clinical signs are most likely related. If you are not convinced that they are all related to a single diagnosis, then you need to keep your problems separate and assess them thoroughly as separate entities, keeping in mind they may or may not be related.
In emergency cases, the problems at the top of your problem list are those that would immediately endanger the patient and must be immediately addressed – remember your ABC of triaging (airway, breathing, circulation). They may then be followed by the problems that act as the diagnostic hooks to reach the final diagnosis/management plan.
| Key concept | |
|---|---|
| Create problem list | Summarise the clinical problems the patient has presented with. |
| Prioritise the problem list | Identify which of the problems are specific – those that are ‘diagnostic hooks’ +/‐ those that must be addressed immediately as the patient’s life is at risk. |
The reasons that might make one suspect that the clinical signs are related to more than one problem include the following:
The chronology of clinical signs is very different, raising the possibility that there is more than one disorder present. It could be one progressive disorder, but it could also be two different disorders.
The problems don’t fit together easily, for example, different body systems appear to be involved in an unrecognisable pattern, for example, as for Erroll.
Other clues that may be relevant to the case. For example, some clinical signs resolved with symptomatic treatment but others did not.
How do I decide what problems are specific?
As indicated previously, specificity is a relative term and will vary with each patient. There are a few clues that you can look for when trying to decide the most specific problems the animal has:
Is there a clearly defined diagnostic pathway for the problem with a limited number of systems or differential diagnoses that could be involved?
For example: vomiting vs. inappetence
The problem of vomiting has a very clearly defined diagnostic pathway (discussed in Chapter 3), whereas there is almost an endless set of diagnostic possibilities for causes of inappetence, and there is no well‐defined diagnostic approach (Chapter 5).
Hence, vomiting is a more specific and appropriate ‘diagnostic hook’ than inappetence.
Could one problem be explained by all of the other problems but not vice versa, or does the differential diagnosis list for one problem include many diagnoses that would explain the other problems but not vice versa?
For example: vomiting vs. jaundice
As mentioned earlier, jaundice is the more specific problem because most causes of jaundice could also conceivably cause vomiting, but there are many causes of vomiting that do not cause jaundice.
Hence, the diagnostic pathway for jaundice is more clearly defined (discussed in Chapter 11), and there are a more limited number of possible diagnoses.
As mentioned earlier – are there clinical signs that indicate this patient is at immediate risk, so they must be addressed prior to the other problems?
For example: severe dyspnoea, shock, severe haemorrhage.
But don’t forget to relate each problem to the whole animal.
Once you have narrowed down your diagnostic options for the most specific problems, you use these to direct your diagnostic or therapeutic plans, but don’t forget to consider the less specific problems in relation to your differential diagnosis.
For example, your specific problem may be polyuria/polydipsia (PU/PD) associated with a urine specific gravity of 1.002 (hyposthenuria), and your non‐specific problem may be anorexia. Hence, when considering the potential differential diagnoses for PU/PD associated with hyposthenuria (Chapter 13), those diagnoses for which anorexia is not usually a feature, for example, psychogenic polydipsia, diabetes insipidus and hyperadrenocorticism, are much less likely than those diagnoses where anorexia is common, such as hypercalcaemia, pyometra and liver disease. It is not always necessary to ‘rule out’ the former diagnoses, but they have a lower priority in your investigation than the latter group.
Thus, the thinking goes: ‘the causes of hyposthenuria are …, …, …, …, …, … (Chapter 13) and in this patient the most likely causes are …, …, …, … (because of the other clinical signs or clinical pathology present).’
In other words, you use the non‐specific problems to refine the assessment of the specific problems. One could claim that this is pattern recognition, and indeed it is to a certain extent. However, the step of clarifying the problem list (and thus not overlooking minor signs) and assessing the specific problems in this manner allows the clinician’s mind to be receptive to differentials other than the supposedly blindingly obvious one that uncritical pattern recognition may suggest (such as thinking every cat with PU/PD must have renal failure). And as we discuss