Dementia isn't always caused by Alzheimer's, Parkinson's, or the better-known vascular and frontotemporal forms of the disease. There are other, rare causes of dementia, one of which is reversible.
Corticobasal ganglionic degeneration
Corticobasal degeneration, also known as CBGD, is an unusual major neurocognitive disorder that often introduces itself with "alien hand syndrome," the loss of control over the motions of one hand. Or sometimes there will be one leg that seems to have a mind of its own. Alternatively, CBGD can be recognized by progressive loss of language, beginning with long pauses before producing fluent, sensible sentences. Loss of language may be accompanied by loss of control over facial muscles. Eventually there are losses of "executive function", easy distraction, poor judgment, and/or repeated motions. Delusions and hallucinations are not part of the disease.
Progressive supranuclear palsy
Progressive supranuclear palsy (PSP), also known as Steele-Richardson-Olszewski syndrome, is a major neurocognitive disorder that affects eye movement, posture, and thought processes. It usually appears between the ages of 50 and 60. There are no MRIs or CT scans that confirm a diagnosis of PSP. It is diagnosed from a vague progression of symptoms that at first defy explanation. There may be falls that occur for no obvious reason. There is fatigue and headache and joint pain. Then there is double vision and difficulty holding a gaze, sometimes with burning eyes that aren't caused by allergies or chemical irritation. There can be sensitivity to light. Speech becomes apraxic, that is, it becomes difficult to string syllables together to form words. Handwriting becomes illegible. Movements become clumsy.
Normal pressure hydrocephalus
Normal pressure hydrocephalus is a form of dementia characterized by gait disturbances, urinary disturbances (either too-frequent urination or an inability to urinate), and dementia symptoms such as decreased attention span, memory loss, and bradyphrenia, slow thought processes. It is caused by a buildup of spinal fluid, and it can sometimes be treated by surgery to relieve the buildup of spinal fluid. People who can't have surgery sometimes can have punctures to the spine to withdraw excess fluid. Normal pressure hydrocephalus is sometimes misdiagnosed as Parkinson's disease. It is important to get the diagnosis right because the condition sometimes can be reversed.
Benson's syndrome, or posterior cortical atrophy (PCA), is a rare condition caused by damage at the back of the brain, where the brain's vision centers are active. There can be difficulties recognizing faces or objects, but there isn't always a problem with loss of reasoning or memory unless Alzheimer's is also active.
Spatial neglect is a syndrome following brain injury in which the patient does not respond to stimuli on the side of the body opposite the lesion in the brain. They may forget to comb one side of their hair. They may ignore things that happen on one side of their bodies but pay attention to what happens on the other. Sometimes the patient will deny ownership of one side of their body. There usually is no loss of memory or reasoning, but recovery from the condition is rare. Nursing home care is often necessary because the patient will not be aware of injuries to or symptoms on one side of the body. For example, someone who suffers spatial neglect may ignore a heart attack because the pain occurs on the left side of the chest. People who have this condition often do not feel that they own it, and fail to participate in their therapy.
Niemann-Pick disease type C
Niemann-Pick disease type C is not a form of Pick's disease (frontotemporal dementia). It is an inherited inability to process cholesterol and other fats that causes them to accumulate in cells in the brain. There can be progressive loss of speech and hearing. There can be sudden loss of muscle tone, difficulty swallowing, spastic movements, ptosis (drooping of one eyelid), psychotic episodes, progressive dementia, bipolar disorder, and major depression that includes delusions, hallucinations, mutism, and stupor.