Just to clarify this point. Dementia is not an illness. Dementia is a symptom which has many causes. Alzheimers disease is the most common. (it is a horrible disease and sorry you were affected.)
There are causes of dementia which are reversable
Dementia-like conditions that can be reversed
Some causes of dementia or dementia-like symptoms can be reversed with treatment. They include:
Infections and immune disorders. Dementia-like symptoms can result from fever or other side effects of your body's attempt to fight off an infection. Multiple sclerosis and other conditions caused by the body's immune system attacking nerve cells also can cause dementia.
Metabolic problems and endocrine abnormalities. People with thyroid problems, low blood sugar (hypoglycemia), too little or too much sodium or calcium, or problems absorbing vitamin B-12 can develop dementia-like symptoms or other personality changes.
Nutritional deficiencies. Not drinking enough liquids (dehydration); not getting enough thiamin (vitamin B-1), which is common in people with chronic alcoholism; and not getting enough vitamins B-6 and B-12 in your diet can cause dementia-like symptoms. Copper and vitamin E deficiencies also can cause dementia symptoms.
Medication side effects. Side effects of medications, a reaction to a medication or an interaction of several medications can cause dementia-like symptoms.
Subdural hematomas. Bleeding between the surface of the brain and the covering over the brain, which is common in the elderly after a fall, can cause symptoms similar to those of dementia.
Poisoning. Exposure to heavy metals, such as lead, and other poisons, such as pesticides, as well as recreational drug or heavy alcohol use can lead to symptoms of dementia. Symptoms might resolve with treatment.
Brain tumors. Rarely, dementia can result from damage caused by a brain tumor.
Anoxia. This condition, also called hypoxia, occurs when organ tissues aren't getting enough oxygen. Anoxia can occur due to severe sleep apneas, asthma, heart attack, carbon monoxide poisoning or other causes.
Normal-pressure hydrocephalus. This condition, which is caused by enlarged ventricles in the brain, can cause walking problems, urinary difficulty and memory loss.