Memory issues have become so intrinsically linked with Alzheimer's disease that even small slip-ups—misplaced house keys, having trouble locating the car in a crowded parking lot—can send aging individuals into a tailspin of worry.
While memory loss is indeed a sign of dementia and a hallmark of Alzheimer's, it is only one of many cognitive symptoms of the disease.
In fact, according to a newly-released analysis from the Mayo Clinic, one out of every ten people with Alzheimer's have little or no problems remembering. Men and women with the so-called "hippocampal sparing" form of Alzheimer's disease are more likely to feel as though they can't control their bodies (or that they are being controlled by some outside force), have vision issues that can't be traced to a specific eye condition, and engage in inappropriate, angry behavioral outbursts. They are also more likely to be male, to start showing signs of cognitive deterioration at a younger age (typically in their 50s) and to decline at much faster rate.
Lack of awareness among doctors and their patients of the existence of this Alzheimer's sub-type means that the estimated 600,000 Americans with hippocampal sparing Alzheimer's may encounter trouble when seeking the source of non-traditional symptoms. "These patients are misdiagnosed more than 50 percent of the time," says lead study author Melissa Murray, Ph.D., assistant professor of neuroscience at the Mayo Clinic's Florida branch in a press release. "They don't have the memory impairment, so a clinician isn't necessarily considering Alzheimer's disease."
Instead, if dementia is suspected, the finger is often pointed at frontotemporal dementia. This can cause an individual with Alzheimer's to miss out on potential treatment opportunities. While there is currently no way to prevent, cure, or reverse Alzheimer's, there are, according to Murray, "drugs now on the market for Alzheimer's dementia [that] could work best in these hippocampal sparing patients—possibly better than they work in the common form of the disease."
Mayo researchers believe they have discovered the root cause of the difference in the outward symptoms associated with hippocampal sparing Alzheimer's.
Alzheimer's disease is thought to be linked to the accumulation of two distinct proteins: amyloid beta and tau. Amyloid beta gathers in between brain cells (neurons) and disrupts communication, and tau tangles amass within the neurons themselves, causing them to weaken and die.
After examining the brains of more than 1,800 individuals with Alzheimer's, study authors found that amyloid beta was widely spread throughout the brain, regardless of their symptoms, but the tau tangles were strategically clustered in the areas that experienced the most damage.
In people with Alzheimer's, this injury tends to occur most profoundly in the hippocampus—the area of the brain that facilitates learning and memory formation. In people with hippocampal sparing Alzheimer's, however, this damage occurs mainly in the frontal and parietal lobes of the brain—the areas responsible for motor control and behavioral regulation.
The question of how to accurately diagnose Alzheimer's in living people has been the source of serious medical debate. Currently, the only way to know for sure whether a person has this particular type of dementia is to perform a post-mortem brain examination.
A new brain imaging test that examines beta amyloid accumulation in a living brain, via a special type of PET (positron emission tomography) scan, was recently developed as a way to help guide clinicians towards a more definitive diagnosis of Alzheimer's. But lingering doubts about the accuracy and usefulness of the test caused the Centers for Medicare and Medicaid Services (CMS) to deny widespread coverage of the scan. Coverage for one scan—which costs somewhere in the neighborhood of $3,000 to $10,000—may only be obtained if it is used to rule out Alzheimer's when a diagnosis is proving especially tricky or to enhance the effectiveness of clinical trail research.
There are definite pros and cons to obtaining an early diagnosis of Alzheimer's disease, including that ability to better plan for future care and obtaining an explanation for disturbing cognitive decline. But with a cure currently out of sight, the lingering question for many families is: What Happens After an Alzheimer's Diagnosis?