In regards to frontal temporal dementia (FTD), what is primarily absent in brain imaging?

In the context of frontal temporal dementia (FTD), the primary characteristic observed in brain imaging is the absence of B amyloid. FTD, which includes a group of disorders characterized by progressive degeneration of the frontal and/or temporal lobes, typically does not exhibit the amyloid plaques that are often associated with other forms of dementia, such as Alzheimer's disease.

In contrast, tau protein abnormalities are more prevalent in FTD, particularly in the form of tau-positive inclusions that are critical for the disease's pathology. Therefore, tau is not absent and is often a significant finding in FTD cases. Similarly, while alpha-synuclein is associated with other neurodegenerative conditions, such as Parkinson's disease, it is not a primary feature that is assessed in the context of FTD.

Thus, the reason that B amyloid is considered to be primarily absent in brain imaging for frontal temporal dementia underscores how FTD differs from other dementias in terms of its underlying pathophysiology and the resultant imaging findings.