On Thursday, the Food and Drug Administration (FDA) approved the use of a radioactive diagnostic instrument for patients under evaluation for Alzheimer's disease. This drug from Eli Lilly (NYSE:LLY) is the first that the FDA has approved to look for tau neurofibrillary tangles (NFTs) in the brain.

What's it good for?

The number of Americans living with Alzheimer's disease is expected to rise from around 5 million in 2014 to around 14 million by 2060. There are no treatments proven to slow the progression of this ultimately fatal disease yet, but a better understanding of NFTs and their association with dementia could go a long way to help.

Physician examining a brain scan.

Image source: Getty Images.

Positron emission tomography (PET) images with lots of NFTs are a primary marker of Alzheimer's and other dementias, but so are amyloid plaques. Lilly and several of its peers have spent billions developing drugs that effectively reduce the formation of amyloid plaques, but this hasn't been proven to help slow down the progression of this ultimately fatal disease.

While NFTs have been associated with Alzheimer's disease at least as long as amyloid plaques, new drug candidates aimed at their reduction haven't been explored as often. Now that Tauvid has been approved by the FDA to help physicians and researchers track NFTs, we could see more development of drugs that aim in this direction.

Currently, the only way to definitively diagnose Alzheimer's is with a post-mortem evaluation of a patient's brain. Eli Lilly and the FDA found Tauvid to be safe and accurate in two trials with terminally ill patients that allowed their brains to undergo post-mortem evaluations following Tauvid imaging.