Alzheimer's disease is a progressive, degenerative disorder that attacks the brain's neurons, resulting in loss of memory, thinking and language skills and behavioral changes. Alzheimer's disease is the most common cause of dementia or loss of intellectual function among people aged 65 and older. However, Alzheimer's disease is not a normal part of aging.
The origin of Alzheimer's disease dates back to 1906 when Dr. Alois Alzheimer, a German physician, presented a case history before a medical meeting of a 51-year-old woman who suffered from a rare brain disorder. A brain autopsy identified the plaques and tangles that today characterize Alzheimer's disease.
Typical warning signs include:
- Memory loss, especially of recent events, names, placement of objects and other new information
- Confusion about time and place
- Struggling to complete familiar actions, such as brushing teeth or getting dressed
- Trouble finding the appropriate words, completing sentences, and following directions and conversations
- Poor judgment when making decisions
- Changes in mood and personality, such as increased suspicion, rapid and persistent mood swings, withdrawal and disinterest in usual activities
- Difficulty with complex mental assignments, such as balancing a checkbook or other tasks involving numbers
But besides those listed above, there may be another sign — a decreased ability to identify odors. Smell tests have been touted as a possible way of predicting Alzheimer's dementia because of a reported association with decreased sense of smell.
Gorden Sun, M.D., is a general otolaryngologist and Robert Wood Johnson/VA scholar at the Ann Arbor VA Medical Center and the University of Michigan. His team has set out to determine whether these beliefs are based on existing high-quality evidence.
They found 30 studies that compared the sense of smell in patients with Alzheimer's and those without the disease or with mild cognitive impairment, a precursor condition. They also reviewed two studies that looked at whether older patients who had lost their sense of smell eventually developed Alzheimer's.
The comparison studies found that people with Alzheimer's did worse on smell tests than people who did not have the illness or those whose cognition was mildly impaired. The theory is that as the disease begins to kill brain cells, this often includes cells that are important to the sense of smell.
Matthew E. Growdon, B.A., M.D./M.P.H. candidate at Harvard Medical School and Harvard School of Public Health, and colleagues investigated the associations between sense of smell, memory performance, biomarkers of loss of brain cell function, and amyloid deposition in 215 clinically-normal elderly individuals.
The researchers administered the 40-item University of Pennsylvania Smell Identification Test (UPSIT) and a comprehensive battery of cognitive tests. They also measured the size of two brain structures deep in the temporal lobes — the entorhinal cortex and the hippocampus (which are important for memory) — and amyloid deposits in the brain.
At the Alzheimer's Association International Conference 2014, Growdon reported that a smaller hippocampus and a thinner entorhinal cortex were associated with worse smell identification and worse memory. The scientists also found that, in a subgroup of study participants with elevated levels of amyloid in their brain, greater brain cell death, as indicated by a thinner entorhinal cortex, was significantly associated with worse olfactory function.
With Alzheimer's disease growing fast among the world's aging population, researchers are increasingly focused on searching for new ways to detect and treat the brain-killing disease in its earliest stages. The possible connection between losing one's sense of smell predicting the onset of Alzheimer's is an intriguing one.
Although the sense of smell can deteriorate because of other reasons, the research offers hope that the odor-detection test might someday be used with other diagnostic tools to help identify those at risk of Alzheimer's.
