There are many fundamental points in clinical decision making, which apply to the approach of all clinical cases. The focus of this session will be on vomiting and diarrhea, using several case examples to illustrate important points in clinical decision making.
Before starting to think about an individual case, it is well worthwhile taking a moment to reflect on your approach to cases. We should all have a logical systematic approach to every case.
How do you think logically through a case?
How do you make diagnostic and therapeutic decisions?
Do you have a systematic approach that would lead you to make the same decisions on a case whether you saw it Monday morning or Saturday afternoon, when you were feeling happy or sad?
How do you gather and process the information and put it all together?
Broadly and simplistically speaking, there are two different ways of approaching a clinical case to reach a diagnosis:
Problem solving; where a list of differential diagnoses are made for each clinical problem, with each differential gradually ruled in or out with diagnostic tests.
Pattern recognition; where the pattern of the signalment, combination of clinical signs and other clinical findings, particularly fit with one differential diagnosis, and this differential is then focused on.
The best clinicians combine both ways of thinking and move back and forth between the two when 'working up' a case.
I like to always start with a complete list of differential diagnoses, of groups of diseases. And then assess the complete picture of signalment, history, physical examination, laboratory and imaging data to try to refine those differentials, and then move your thoughts from the more general to more specific diseases. If results of investigations don't fit with your top differentials, then move back to your differential diagnosis list and see what you may have missed.
Differential Diagnoses
Chronic vomiting differentials:
Extra-intestinal
Pancreatic disease - pancreatitis, EPI
Renal disease
Liver disease
Hyperthyroidism
Environmental factors
Intestinal
Infectious
Helicobacter
Inflammatory
Diffuse (e.g., IBD)
Focal; granuloma (e.g., FIP, eosinophilic sclerosing fibroplasia)
Neoplastic
Diffuse (e.g., LGAL)
Focal (e.g., lymphoma, adenocarcinoma, mast cell tumour)
Partial obstruction
Foreign body
Intussusception
Extra-intestinal compression
Chronic diarrhea differential diagnoses:
Extra-intestinal
Pancreatic disease - pancreatitis, EPI
Hyperthyroidism
Environmental factors
Intestinal
Infectious
Parasitic
Protozoal
Giardia
Tritrichomonas
Coccidial
Isospora
Cryptosporidia
Bacterial
Campylobacter
Clostridia
Viral
Syndromes involving FeLV, FIV, coronavirus
Inflammatory
Diffuse (e.g., IBD)
Focal; granuloma (e.g., FIP, eosinophilic sclerosing fibroplasia)
Neoplastic
Diffuse (e.g., LGAL)
Focal (e.g., lymphoma, adenocarcinoma, mast cell tumour)
Partial obstruction
Foreign body
Intussusception
Extra-intestinal compression
Assess the Clinical Picture
Signalment
Young animals are more susceptible to dietary and infectious causes, and more likely to ingest foreign bodies
Older animals are more susceptible to systemic disease and neoplasia
Purebreds are more susceptible to some diseases like Tritrichomonas and FIP
History
Previous clinical signs or diagnosed disorders
Chronicity of signs
Environmental conditions, including overcrowding and immune compromise increase the risk of infectious causes
Other affected animals in the household
Large or small intestinal diarrhoea
Vomiting and diarrhoea or just one or the other
Normal/increased/decreased appetite
Presence of weight loss
Physical examination
Demeanor
Vital parameters
Body condition
Coat condition
Hydration
Presence of icterus
Presence of goitre
Abdominal discomfort
Palpable abdominal abnormalities
At this stage, you should summarise the key features of the case. For example,
Chronic large intestinal diarrhoea
Otherwise well, no exam abnormalities
Very young cat
Pedigree
Use pattern recognition to then think which differential diagnoses are most likely - think about the clinical clues. What is most likely given:
Signalment
History
Physical exam
Can you narrow down differentials & prioritise?
Next step: further investigation? Or treatment trial? What investigation or treatment?
In the above example, the key features would make infectious disease most likely. If we then move from the 'general' to the 'specific', most likely differential diagnoses would be Giardia and Tritrichomonas foetus. This would lead us to faecal testing for these organisms, and perhaps a trial treatment for Giardia and dietary trial pending results.
If further diagnostics are then performed, this step of evaluating the clinical clues in light of the whole clinical picture, before deciding on the next step, should be performed after each diagnostic.
What are the Next Diagnostic Options?
Further diagnostic options are similar for both chronic vomiting and diarrhoea, with the addition of faecal tests in cases of diarrhoea.
Faecal parasitology
Faecal culture
Giardia
ZnSO4 flotation
ELISA
PCR
Tritrichomonas foetus
Rectal swab wet prep
Special culture
PCR
Haematology/biochemistry/T4
B12/folate/TLI/fPL
FeLV/FIV
Abdominal radiographs
Abdominal ultrasound
Gastrointestinal biopsies
Surgical vs. endoscopic
At each diagnostic test, think about what you are looking for before performing the test. For example, with abdominal ultrasound:
Intestine - presence of a mass, wall thickness, loss of layering
Liver - size, echogenicity, gall bladder contents and wall, bile duct diameter
Pancreas - presence of irregular margin, increased size, hypoechogenicity, cavitary lesions, hyperechoic mesentery & peripancreatic fat, pancreatic duct dilation, ileus
Mesenteric lymphadenopathy, free fluid
There are a couple of rules used in human medicine that can help to keep a logical approach when performing diagnostics:
Simpson's rule = Only perform a test if the outcome of that test will change your management of the case
Suttons's law = Always perform the test first that is most likely to give you the diagnosis
Both these rules emphasize the importance of thinking carefully before performing diagnostics, thinking about what differential diagnoses are most likely, and what the outcome of performing each diagnostic may be.
The final step is to think: "Does everything fit together?"
Are the signalment, history, clinical signs typical of what you are considering the most likely differential diagnosis?
If the outcome either of a treatment trial or diagnostic tests does not fit with your most likely differential diagnoses, then revisit your master list of differential diagnoses to see what you may have missed.