Unfortunately I cannot give you a clinical diagnosis over the internet, without seeing you or your test results
Other tests to consider would be an evaluation to exclude cerebral
vasculitisNecrotizing vasculitis as a cause - such as blood sedimentation rate, antinuclear antibodies, Behcets disease (a form of vasculitis), and maybe an angiogram
I assume an MR angiogram was done with the MRI to exclude any major vascular narrowings?
While you do not appear to meet criteria for a diagnosis of MS based on the presence of old UBOs and no clinical attacks, other tests such as evoked potentials, and cerebrospinal fluid analysis can help exclude an inflammatory/demyelinating problem
Migraine can certainly cause this MR appearance, and may indeed be the correct diagnosis after the excluding the above diseases. Migraine can change over time as one gets older, and may even cause transient focal neurological deficits with or without headache
A trial of several weeks is necessary to see if you are benefitting from a prophylactic medication, and treatment may continue indefintely based on a good response
There is no standard algorithm for drug treatment - one may argue that tackling the mechanism of the migraine from 2 different angles may produce more benefit, and in shorter space of time
Good luck