include the following:
The body system always involved when a patient vomits is the gastrointestinal (GI) system (define the system).However, it may be directly involved due to primary pathology of the gut, such as parasites, inflammation, neoplasia and foreign body. The system is thus refined as primary (structural) GI disease.Or vomiting may be occurring due to dysfunction of non‐GI organs, such as the liver, kidney, adrenal glands and/or pancreas. The system is thus refined as secondary (functional) GI disease.
The body system that is always involved when a patient has generalised weakness is the neurological/neuromuscular system (define the system).However, in refining the system, it may be directly involved due to primary neurological/neuromuscular pathology (e.g. inflammation, toxins, neoplasia and infection).Or the neurological/neuromuscular system may be malfunctioning due to the effect of pathology on other organs, causing metabolic derangements that impair neurological/neuromuscular function, such as hypoglycaemia, anaemia, hypoxia and electrolyte disturbances. This is thus refined as secondary neurological/neuromuscular disease.
Why is it so important to define and refine the system?
The range of diagnoses to consider, diagnostic tools used and potential treatment or management options for primary, structural problems of a body system are often very different compared to those relevant to secondary, functional problems of that system.
Investigation of primary, structural problems often involves imaging the system in some manner (radiology, ultrasound, advanced trans‐sectional imaging, endoscopy and surgery) and/or biopsy. Routine haematology, biochemistry and urinalysis are often of little diagnostic value. For secondary, functional disorders, on the other hand, haematology and biochemistry are often critically important in progressing our understanding of the case and reaching a diagnosis.
Failure to consider what body system is involved (define the system) and how it is involved (refine the system) can often lead to wasted time and money. This can delay treatment, prolong the disease, prolong the patient’s suffering, sometimes potentially endanger the life of the patient, and may increase unnecessarily the costs to the client, frustrate the vet and client and potentially impair the relationship between vet and client. (Notice a recurring theme here?)
In fact, if you do nothing else when assessing a case before seeking the diagnostic ‘pattern’, ask yourself for each of the specific problems, What system could be involved (i.e. define the system), and how – primarily or secondarily? (i.e. refine the system). This simple question will immediately open your mind to diagnostic possibilities you may never have contemplated if you were just focusing on the ‘pattern’.
Other examples include the following:
Chronic cough – cardiac or respiratory system? (Chapter 9)
Jaundice – due to a haemopoietic (haemolysis) or hepatobiliary disorder? (Chapter 11)
Cardiac arrhythmia – is it due to primary (structural) cardiac disease – for example, dilated cardiomyopathy? Or extra‐cardiac disease – for example, gastric dilation and volvulus, splenic pathology? (Chapter 7)
PU/PD – is it due to primary polydipsia (the patient wants to drink) or primary polyuria (the patient has to drink)?If due to primary polyuria – is this because of primary (structural) renal disease (e.g. chronic kidney disease) or extra‐renal dysfunction, for example, diabetes mellitus, hypercalcaemia and hypoadrenocorticism? (Chapter 13)
An alternative, although closely related, question for some problems is, Is the problem local or systemic?
Epistaxis – due to local nasal disease or systemic disease – for example, coagulopathy and hyperviscosity? (Chapter 12)
Melaena – GI bleeding due to local disease (ulceration – which in turn may be due to primary or secondary GI disease) or systemic disease, for example, coagulopathy? (Chapter 12)
Seizures – due to local brain disease, for example, neoplasia, infection/inflammation or systemic disease, for example, electrolyte disturbances or intoxication? (Chapter 8)
How to differentiate primary from secondary system involvement?
There are often clues from the history and/or clinical examination that help you define and refine the body system involved. Or you may not be able to answer this question until further diagnostic tests are performed. But just asking the question ensures that you remember that body systems can malfunction due to direct pathology of that system, for example, inflammation, neoplasia, degeneration, infection or due to functional problems where factors not directly related to the body system can impact on its function.
Figure 2.5 Clinical reasoning step‐by‐step: define the location.
Define the location is the step which may or may not be needed during your problem‐based assessment. For some problems it is very important. For others, the Define the location question is addressed as part of the Define the system assessment. This will become evident in some of the case examples provided later in the book.
Example: having determined that vomiting is due to primary GI disease, where in the GI tract is the lesion located (define the location)?
In this example, by asking this question, you will select the most appropriate method either to answer the question or to move on to the next step.
For example, if you believe that your history and physical examination and other ancillary data indicate a lower small intestinal lesion, endoscopy may not be an appropriate method of visualising the area or obtaining biopsies as the scope will not reach the ileum. However, if all of the information you have suggests a gastric or duodenal lesion, endoscopy may be appropriate if available.
Other examples include the following:
Vomiting due to secondary GI disease – liver, kidney, adrenals and pancreas? (Chapter 3).Brutus is an example of secondary GI disease due to liver pathology.
Hind limb weakness is due to neurological dysfunction – is the lesion in the spinal cord (and where), peripheral nerves, muscles or brain? (Chapter 7)
Haematuria – from urethra, prostate, bladder or kidneys? (Chapter 12).Errol is an example of haematuria due to bladder pathology.
Figure