A series of repeated TIAs characterized by identical neurological deficits is
often a warning sign that a major vessel contains an unstable plaque on which
thrombi are repeatedly forming (and causing ischemia) and then fragmenting (and
allowing blood to flow again). The neurological features of these TIAs are often
indicative of the deficit, or part of the deficit, that would be produced by the
impending "completed" stroke.
It is less likely that cardiac emboli will repeatedly produce the same deficits--they
are able to travel to any part of the brain. In some individuals, TIAs may result
from decreased perfusion of large arteries that are already partially occluded
by plaque. This might occur with fluctuations in blood pressure produced by overzealous
medication or by various cardiac arrhythmias.