More than 50 conditions are associated with dementia, including degenerative neurological disorders (e.g., Alzheimer's disease), vascular disorders (e.g., multi-infarct disease), inherited disorders (e.g., Huntington's disease), and infectious diseases (e.g., HIV/AIDS).
Alzheimer's disease causes 50-70% of all cases of dementia. Alzheimer's is the progressive deterioration of areas in the brain essential for learning and memory.
Lewy body dementia is similar to Alzheimer's but may progress more rapidly. Abnormal brain cells called cortical Lewy bodies occur throughout the brain and produce symptoms.
Pick's disease is also similar to Alzheimer's. In most patients, the frontal and temporal lobes of the brain atrophy. This illness usually affects people between the ages of 40 and 60.
Amyotrophic lateral sclerosis (Lou Gehrig's disease), Huntington's disease, and Parkinson's disease are also associated with dementia. Progressive supranuclear palsy produces clinical features similar to Parkinson's disease and often causes severe cognitive difficulties.
HIV/AIDS is a viral infection that may lead to AIDS dementia complex during late stages of the disease. Antiretroviral therapy has reduced the incidence of AIDS dementia.
Creutzfeldt-Jakob disease (CJD) is a fatal infectious disease characterized by brain tissue that is filled with holes and looks like a sponge under microscopic examination. The initial symptom of CJD is usually a vague personality change, followed within weeks or months by rapidly progressing dementia. The dementia is often accompanied by other central nervous system problems, such as visual disturbances and involuntary jerks of the limbs (myoclonus).
Multi-infarct disease is the second most common cause of irreversible dementia. In this condition, multiple strokes (infarcts) lead to a progressive decline in cognition. Multiple infarct dementia is more common in men over 50 years old.
Alcoholism can lead to vitamin B1 (thiamine) deficiency, seizures, and head injuries that produce dementia.
Chronic drug abuse also can cause symptoms of dementia. Drugs that may cause dementia include the following:
- Cough suppressants
- Monoamine oxidase inhibitors
- Tricyclic antidepressants
Disease caused by viral, bacterial, or fungal infection can lead to impaired cognitive function. In some cases, appropriate treatment of the underlying condition can reverse symptoms. Infections that may cause dementia-like symptoms include meningitis (inflammation of the membranes that cover the brain and spinal cord; bacterial, viral, or fungal) and encephalitis (inflammation of the brain caused by viral or bacterial infection).
Neurosyphilis dementia may result from late-stage syphilis. This disease also may cause heart problems, tremors, loss of muscle coordination (ataxia), paralysis, and blindness and damage is irreversible.
Structural abnormalities that can produce dementia include brain tumors located in areas involved with cognitive function, chronic subdural hematoma resulting from head injury (common in the elderly and alcoholics), hydrocephalus, and normal pressure hydrocephalus. Surgical treatment can relieve symptoms.
Metabolic disorders such as low level of thyroid hormone or thyroid stimulating hormone (hypothyroidism), low blood sugar level (hypoglycemia), high blood calcium level (hypercalcemia), and liver disease can affect cognitive function. Treating the underlying condition can restore function.