One example would be when someone presents with inability to walk far and have associated features of shortness of breath and chest pain.
You might think this could be caused by either heart disease such as ischaemic heart disease (IHD) or lung disease eg chronic obstructive airway disease (COAD). It is true that both IHD and COAD can prevent someone from walking far. Hence, you would order CXR and ECG stat.
We need to think broad before wasting precious investigations. Is there other diseases that might cause someone unable to walk far?
One possible explanation that should be included in differential diagnosis would be osteoarthritis of knee or hip :). If you don't think this as one of the possible causes, you will look foolish in front of the patients and consultants.
Another example is shoulder pain. Pain in the shoulder joint can be attributed to the shoulder pain but there are other possible causes of shoulder pain.
My usual approach is to diagnose the causes systematically. Try to find out local causes, distant causes and referred pain.
- rotator cuff (degeneration, tendon rupture, calcific tendonitis)
- subacromial bursa (calcific bursitis, polyarthritis)
- capsule (adhesive capsulitis)
- Glenohumeral joints (synovisitis, osteoarthritis, dislocation)
- head of humerus (tumour, osteonecrosis, fracture/dislocation)
- Acromioclavicular joint - osteoarthritis
- Sternoclavicular - synovisitis, osteoarthritis and dislocation
- Cervical spondylosis
- Cardiac ischaemia
- Anything that can irritate the phrenic nerve (liver, pancreas, pleura etc)
If you are stuck and unable to think of other possible causes of any symptoms, asking system review questions will help to buy time and hopefully reveal useful clue to the diagnosis.
Besides diagnosing medical condition, we tend to jump straight into conclusions whenever we met any strangers in life. We immediately judge someone based on their appearance, attitude or based on how other people perceive the person.
Anyway, the message that I would like to convey in this post is to think broad and collect enough evidence before making your own opinion towards anything in life.