A neurologist would be the appropriate referral.
As you can
imagine, there are many reasons for memory loss
. This can include metabolic diseases, thyroid diseases, various causes of dementia, infections, stroke, Parkinson's disease to name but a few.
Tests to consider would be a metabolic panel, thyroid tests, blood count, vitamin b12 level, liver tests as well as urine tests. A repeat MRI as well as imaging of the neck vessels should be considered.