We now know that there's a link between insulin resistance and Alzheimer's disease. And since insulin resistance is related to physical activity, that might help explain why physical activity has also been linked to Alzheimer's disease. Admittedly, I'm stretching things quite a bit to fill our knowledge gaps but you have to admit, it's plausible.
But in the meantime, what do you do? How do you know if you have it or not? Back in the day when I was in training and we didn't have CT/MRI/PET scanners everywhere, we thought long & hard before sending someone for imaging. After all, the radiographic image didn't so much as prove/confirm the diagnosis of Alzheimer's disease as much as it "ruled out" other conditions that also lead to memory loss.
More recent advances now allow us to consider hippocampal volume as well as functional metabolism, eg glucose uptake. Pittsburgh Compound B is the first agent allowing us to look for beta amyloid plaque buildup, what's theorized as the cause of Alzheimer's disease. However, it's general use is limited to due its very short half-life.
With time & money, more & more compounds are being studied as diagnostic imaging agents. Research regarding the efficicacy of florbetapir was just published in this week's issue of JAMA. Florbetapir, with a longer half-life than Pittsburgh Compound B, was able to confirm the presence & density of pre-mortem beta amyloid with post-mortem autopsies, the only true gold standard for diagnosing Alzheimer's disease, with 96% accuracy in 29 individuals tested an average of 99 days prior to death.
Coincidentally, the manufacturers of florbetpir took their product before the FDA yesterday. But in a classic case of the glass is half empty/full, Medscape titled their post as FDA rejecting florbetapir while MedPageToday, writing about the same meeting & vote, titled their article as FDA approves florbetapir with caveat. So which is it? In fact, they're both right, in a way. The FDA advisory committee did vote 13-to-3 against approving florbetapir. However, in a second vote, they also voted 16-to-0 for approval if and only if the manufacturer stepped up with education & training to help radiologists interpret the images correctly.
So where does this leave us? Don't forget that we still don't have a cure for Alzheimer's disease. The four pharmaceutical agents broadly used today (five, if you count the original four-times-daily, potentially-dangerous-to-the-liver drug) only slow down the progression of disease, and that's only if you're lucky enough to be a responder and look at the statistics funny (just ask the folks at NICE who recently changed their minds without benefit of any new data).
Why spend money making a diagnosis when there really aren't any good treatment options available. Why not just put those funds to use caring for the patient and family? Or better yet, use those funds to encourage lifestyle changes to decrease one's risk of developing Alzheimer's disease!