How does the presence of 1-3 microbleeds on MRI influence your choice of anti-amyloid therapies for patients with MCI or mild AD?

1-3 microbleeds is a small number, and the question does not specify that to be suspicious for amyloid angiopathy, the microbleeds should be cortical/subcortical, not deep (as seen in hypertensive individuals). This number, assuming that there are no signs of a larger hemorrhage nor superficial siderosis, would not be an absolute contraindication to anti-amyloid therapy, but I would feel the need to counsel the patient and family that a higher incidence of ARIA-E and ARIA-H could occur. I would also test the patient for APO-E status, as E4/E4 or even one E4 gene would also increase the risk.

It depends on timing and location. 1-3 microbleeds before initiation of therapy is contraindicated for starting therapy. However, 1 to 3 microbleeds after initiation of therapy should be looked at carefully. Locations of microbleeds in the cortical areas, close to the surface is a likely indication of CAA, whereas deeper microbleeds are possible hypertensive bleeds and not as concerning.