The white matter are the parts of the brain which contain axons, as opposed to gray matter, which contains the neuron cell bodies themselves. Axons are the part of the neuron which transmit information to other neurons. White matter disease is a generic term which simply means that the white matter does not look normal. It does not reference any specific disease entity itself. Causes of white matter disease range from multiple sclerosis (MS), which is unlikely in a 75 year old person, to chronic ischemic disease (low blood flow to the brain), which is very common in a 75 year old person. Depending on the cause, the treatment differs, but in general there is no treatment. The best way to prevent ischemic injury to the brain is similar to prevention of heart disease: eat well, get plenty of exercise, lower your cholesterol, control your diabetes, lower your blood pressure, etc.