Can a progressive case of dementia be determined by a spinal tap, blood testing, or an mri during very early onset or at all?

Maybe.: Dementia is not one disease. Dementia has many causes - some of them can be detected by brain imaging or suggested by blood studies. Most dementia is of the Alzheimer's type- there is no specific blood or imaging study for this type of dementia.

Yes,but: yes you can rued out a lot of causes of dementia that way ,but still the most common cause in unknown.

Probably: not. There is no effective "screening" test for dementia. It usually comes to light due to clinical symptoms, and additional testing may be done to exclude other causes.

Evaluation.: It is best to diagnose dementia ASAP, so appropriate therapeutic interventions can be initiated. The Gold Standard test would be a PET scan, but the less accurate SPECT may be helpful. A neuropsychological test battery will also pinpoint, and EEG can differentiate. Blood tests to check for reversible entities are advised. Spinal fluid may pick up Alzheimer markers.

Assessment: There should be an extensive workup for patients who exhibit signs of dementia, which includes a number of different diagnostic tests, which may include a lumbar puncture, blood tests and imaging. A neurologist would be appropriate to consult if this is a question.