list
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 later in this chapter, the particular steps you take in assessing the specific problems also decrease the risk of pattern‐based tunnel vision and confirmation bias.
How likely is a diagnosis?
Priority is also influenced by the relative likelihood of a diagnosis. Common things occur commonly. Therefore, although you shouldn’t dismiss the possibility of an unusual diagnosis by any means, the priority for the assessment is usually to consider the most likely diagnoses first, provided they are consistent with the data available.
The problem‐based approach
Problem‐based approach means different things to different people, and you may have already read about or been to courses where it was discussed. Some regard the problem‐based approach as meaning ‘write a problem list, then list every differential possible for every problem.’ Not a feasible task unless you have an amazing factual memory and endless time! Others view the problem‐based approach as meaning ‘write a problem list, then list your differentials.’ This is really just a form of pattern recognition, but at least it makes a good start by formulating a problem list.
The basis of this book is the concept of logical clinical problem‐solving (LCPS). This approach provides steps to bridge the gap between the problem list and the list of differential diagnoses via a structured format. The problems should be investigated by rigorous use of the following questions as illustrated in Figure 2.2:
What is the problem? (Define +/‐ refine the problem – some problems do not need to be refined, others do.)
What system is involved, and how is it involved? (Define and refine the system.)
Where within the system is the problem located? (Define the location.)
What is the lesion? (Define the lesion – the differential list.)
The answers to these questions or the pursuit of the answers will determine the appropriate questions to ask in the history. They may alert you to pay particular attention to aspects of the physical examination, and/or they may indicate the most appropriate diagnostic test to use to find the answers as well as prepare you intellectually to assess the results of diagnostic procedures.
