At the start of every viva case, and written case for that matter, you will be given a short clinical history. The aim isn't to give the game away, rather orientate you and frame the case. In some cases it is more poignant than others. Usually, you will be given an age, a gender and short statement about why they are in your department.
I would start my viva presentation by repeating this back, and I know many candidates do the same. The reason for me was that I would have an additional 10 seconds scanning and thinking time, and if I repeated the history back then I was less likely to forget it. The latter is the key to many cases, and will be the difference between passing and failing a case.
Let's look at a few examples. This discussion is general concepts only, designed to show where your application of the history can help you close the case. Keep in mind that every case will have it's finer details which will need to be teased out.
Clinical history: 70 year old male presents with non-specific pain.
Case: Diffuse sclerosis of the axial skeleton on plain film.
The differential you offer in this case (which could be seen in the chest or the abdominal viva) will be tailored by the history, most notably the patient's gender and age. While it can be tempting to call osteopetrosis or metabolic bone disease, these are rare entities and your first consideration in a 70 year old patient should be diffuse skeletal metastases. This is a male patient - and you should be thinking prostate cancer metastases. Equally, in a female patient - think a breast primary.
Clinical history: 55 year old female patient with a growing lump
Case: Soft tissue lesion of the lower limb, predominantly fat signal on MRI (small area of enhancement)
The age of the patient is paramount when assessing a soft tissue lesion or a bone tumour. We know that in an adolescent male patient, a bone lesion with an aggressive periosteal reaction is osteosarcoma or Ewings sarcoma until proven otherwise. The patient in this case is in middle age, and we can knock out some differentials but others still remain firmly on the list. I think when you see any mass lesion, it is important to ask yourself "could this be cancer?". There may be the temptation to call a predominantly fat containing (and strange looking) lesion a lipoma, but if it is growing in size you need to raise the possibility of it being a low grade liposarcoma.
Clinical history: 25 year old male patient who is acutely unwell with cough
Case: Cavitating upper zone consolidation on a CXR
Cavitating lesions carry a wide differential. It covers everything from neoplasm to infection to vasculitis. It can be tough to offer a useful differential list in a case where it seems so general. So let's bring it back. The patient is 25, so while we can't definitely say this isn't a malignancy we are favouring a benign aetiology because it is more common. You know the patient is acutely unwell, which also goes along with infection. If the lesion is solitary, with poorly defined margins and perhaps some nodularity - go with infection with a short differential list. It would also be pertinent to offer the possible organism. In a previously well immunocompetent young adult - think staph aureus or tuberculosis in the upper lobes. TB is important to flag as there are public health concerns and contact precautions. I think in this case it is reasonable (and safe) to recommend progress imaging to ensure resolution, and perhaps a CT. If it comes up and there are tree-in-bud nodules then you can call TB and be set.
Clinical history: 30 year old female patient with chest pain and constitutional symptoms
Case: CT aortogram
Before the case even hits the lightbox you can formulate a differential list for this one. There are only so many reasons why a 30 year old woman would be having an aortogram - trauma, vasculitis, congenital. Pair it with the history of constitutional symptoms and you are already thinking vasculitis. All you need to do is describe the thickening of the aortic arch and the great vessels and you are at your diagnosis of Takayasu arterities. Case down. Next!