Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine and obtain a history and review the MRI, I can not tell you what the exact cause of the symptoms is nor what the implications of the MRI findings are. However I will try to provide you with some useful information.
Thre are multiple causes for white matter hyperintensities or so-called plaques in the brain. Most often, in general, these are due to what is called "chronic small vessel disease", literally meaning diseased small vessels that supply blood flow to the brain. This is not an uncommon process in the brain and increases with age, and would be distinctly unlikely in a 26 year old
Other causes of plaques in the brain can be migraine. People with migraine often have plaques on their MRI that are of unclear cause or significance.
Other causes of plaques on MRI can usually be distinguished based on history and symptoms, such as symptoms of neurologic deficit (for example arm weakness or difficulty walking etc). These can also be distinguished based on the MRI appearance. These include, but are not limited to, multiple sclerosis as you mention above, other demyelinating disease, and inflammatory processes such as vasculitis. One specific disorder that is associated with both hearing loss and white matter abnormalities is called Susac's disease, but headache, confusion and other symptoms would be present, and it is associated with very specific MRI findings.
The diagnosis of MS is made based on a variety of factors, most importantly the history, examination and the specific findings on MRI.
Drug overdose, if it leads to low blood pressure with subsequent hypoxic-ischemic brain injury, could theoretically lead to multiple spots in the brain, with a specific pattern called a watershed pattern.
The different causes of white matter hyperintensities can be determined to some extent by interpretation of various sequences of the MRI. Other investigations are sometimes necessary to distinguish the various causes of white matter lesions. A lumbar puncture is sometimes necessary, in which fluid from around the spine and brain is taken out and analyzed with various tests. Angiogram is done if a vessel abnormality is suspected. Other neurometabolic disorders may be investigated for depending again on the exact history, examination, and MRI findings.
Continued evaluation by a neurologist is recommended.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
I stand corrected. It seems she has had some left side weakness/heaviness for the past while. Usually a couple times a week.