White matter hyperintensities (WMH) on MRI (T2W and FLAIR sequences) are seen in several conditions. The most common among them (from more common to less common) are: 1. Migraine, 2. Small vessel ischemia, 3. Multiple sclerosis
Here you can see a FLAIR MRI image showing periventricular hyperintense lesions (right more than left) in a 25-year old woman with a 2-year history of migraine without aura.
So, if you see multiple white matter lesions on MRI, do not think of multiple sclerosis in all cases. In younger people, consider migraine, and consider small vessel ischemia in older people, especially those with high BP or diabetes.