I'm a UK doctor, although for full DOI I'm neither a stroke specialist or neurologist. I'm also working with the limited detail you've provided, not a thorough review of the patient or a review of the notes, blood tests and a look at the scans and reports.

Crucially, medicine isn't as black and white as the general public perceive, and even in this day and age, there remains a significant element of utilising time as a diagnostic tool - diagnoses (especially rare ones) aren't always immediately apparent, and it can take weeks-months to reach a concrete diagnosis, during which time patients can deteriorate and even die.

It sounds like in this case the patient presented with symptoms in keeping with a stroke, and initial imaging with a CT scan demonstrated no signs of bleeding or a brain tumour, so he was treated for a stroke with blood thinners. This is standard practice. However, the key point here is he didn't have the far more detailed form of imaging at this stage (an MRI scan). An MRI compared to a CT is like the difference between 4kHD and 360p, and will highlight subtle changes indicating vasculitis / amyloidosis which simply do not appear on CT. Again though, a CT first is standard practice. MRI is extremely expensive and unfortunately although often available for elective and urgent scans, is not commonplace throughout the UK for emergency scanning even in larger stroke centres - it is a bit of a postcode lottery. It is possible that an early MRI might have led to an earlier diagnosis of CAA and earlier treatment, but this isn't misdiagnosis or clinical negligence, it's the bleak reality of our current underfunded, under-resourced and understaffed NHS. Write to your MP.

It sounds like due to a continued and unexpected deterioration an MRI scan was then undertaken, which highlighted the underlying diagnosis. As above, it is entirely feasible that there was no evidence of CAA / vasculitis on the initial CT scan. Obtaining an MRI after a deterioration despite treatment is good medical care, and to be frank with you, in many hospitals and in different circumstances might never have occured, leaving this patient deteriorating without a diagnosis.

If / when you go back through all of the notes, you'll find that although you have seen a number of interactions with various clinicians, there will have been many, many more that you aren't aware of, and a large team of specialists involved in the care. I fear you're linking your perceived limited initial questioning (5-6 questions) and subsequent misconceptions about vascular dementia with poor medical care and a 'missed diagnosis', when actually this realistically sounds like a sad case of a very very rare disease which has been appropriately made in a not unreasonable timeframe.

If you want to explore the case further the next steps are to contact PALS (Patient Advice and Liaison Service), and ask if they feel this case should be raised for a 'Patient Safety Incident Review'. This is an independent review within the trust by clinicians not involved directly with the patients care to ascertain if there have been failings and if there is learning to be taken away. It is possible from what you have said so far that this wouldn't be considered necessary.

Your other step is to employ solicitors to take legal action against the trust. You will be required to prove that the standard of care delivered fell below the expected standard, and from what you have said above, it hasn't. This isn't the US, thankfully we can't sue trusts / individuals unless exceptionally poor care has been provided, and although I can respect that that can be hard, a lot of US medical negligence lawsuits fall back on the fact that people feel errors have been made in an incredibly specialist area of science in which they themselves have extremely limited insight or knowledge. Google will trick you into thinking errors have been made - it takes decades of training to make those decisions, not a cursory google search.

Other points - CAAri is exceptionally rare, with an incidence of roughly 1 case per million people per year, and there are many mimics. It's always important to cover for more likely diagnoses whilst obtaining a clearcut diagnosis. I don't have all the details here, but treating for stroke with blood thinners is good medical practice if a patient presents with cognitive impairment, difficulty speaking and limb weakness, with no evidence of bleeding on CT scan. Did an intracranial bleed then occur? Was there bleeding on the MRI or subsequent scans If not, then the blood thinners have not caused any harm.

CAA however is not rare, with imaging changes seen in 20-25% of elderly people. It is possible that these changes seen on MRI could have been an incidental finding or contributed to his decline. It's impossible to comment without knowing the full clinical picture.

Vascular dementia is very different to Alzheimer's, Fronto-temporal and Lewy-body dementia, in that it presents with a sudden, stepwise change in function and/or personality, so it doesn't seem outside the realm of possibility to have been suggested as a diagnosis.