Alzheimer disease is a chronic, incurable brain disorder characterized by progressive loss of brain tissue and function. Early Alzheimer disease primarily affects intellectual functions, also known as cognitive functions, such as memory and planning. As the disease progresses, however, it directly or indirectly affects other body systems. The Alzheimer's Association estimates that up to 5.5 million men and women in the United States are living with Alzheimer disease as of 2017.
Central Nervous System
Alzheimer disease is principally a disease of the central nervous system, which includes the brain and spinal cord. Although the cause of Alzheimer disease remains poorly understood, specific brain abnormalities have been identified in patients with the disorder. Amyloid plaques, composed of specific proteins and pieces of dead brain cells, progressively accumulate in the brain tissue. A naturally occurring brain protein known as tau also accumulates abnormally, causing brain cells to malfunction and eventually die.
Loss of functioning brain tissue that occurs with Alzheimer disease initially causes problems with memory and learning. As the disease progresses, intellectual function, personality and mood are increasingly affected and seizures may develop. Individuals with Alzheimer disease become increasingly dependent on others over time because they forget how to perform the basic tasks of daily living. With late-stage disease, people lose their sense of self and present circumstances. Those with advanced Alzheimer disease typically do not recognize loved ones and lose the capacity to contemplate, plan, rationalize, organize and interact with their environment.
Alzheimer disease adversely affects the digestive system in several ways. According to a review article published in 2013 in the "Archives of Gerontology and Geriatrics," swallowing difficulties commonly occur in Alzheimer disease. These difficulties often occur fairly early in the disease, compared to other types of dementia. People often have difficulty eating without choking because of swallowing difficulties. Poorly coordinated swallowing can cause accidental entry of food or liquids into the airways, which may lead to pneumonia. Pneumonia remains a common cause of death among people with Alzheimer disease.
People living with Alzheimer disease may develop an impaired sense of smell, which also interferes with the sense of taste. Eating may become problematic due to these impairments. Bowel control is also adversely affected with Alzheimer disease. Fecal incontinence occurs in most people with advanced disease.
People with advanced Alzheimer disease lose the ability to use their muscles in purposeful ways. Persons with late-stage disease typically lose the ability to walk. The ability to maintain posture to sit safely in a chair may also be lost. The muscles become increasingly rigid as control of the muscular system declines. Falls and other accidental injuries related to declining muscular function are common among people with Alzheimer disease. A review article published in May 2011 in "Expert Review of Neurotherapeutics" reports that some research suggests that subtle, gradual loss of neuromuscular function -- such as declining dexterity and balance -- might develop before noticeable memory loss or other common intellectual symptoms of early Alzheimer disease.
Other Body System Effects
Alzheimer disease can cause other body system effects. Reduced circulatory system response to changes in body position can lead to dips in blood pressure upon sitting up or standing, a condition called orthostatic hypotension. Loss of bladder control also frequently occurs with advanced Alzheimer disease. Lack of mobility might lead skin complications, such as pressure sores and infections. Depression often accompanies Alzheimer disease, and sleep disturbances are common. As the course of Alzheimer disease varies among individuals with the condition, other possible body system effects can also occur.