To answer your query the MRI findings are suggestive of small vessel disease
. To simplify further it means that the smaller vessels of deep brain matter have decrease in lumen size which results in hampered blood supply resulting in the changes described. It is most commonly seen in patients with long standing hypertension
and as in your case due to vasculitis
. I can definitely say these are not responsible for your ortho static hypotension
which can most likely to be due to autonomic neuropathy which is seen in Sjögren's syndrome.