Diagnostic accuracy is low, even for Alzheimer’s!

This email may be of interest to the armchair researchers among us and those following progress on brain imaging for Alzheimer’s and other amyloid-based pathologies.

For the last several years, researchers at major medical centers have had access to amyloid PET scans.  These scans indicate if there’s amyloid in the brain.  Amyloid is one of two proteins involved in Alzheimer’s Disease.  Just because there’s amyloid in the brain doesn’t mean someone has Alzheimer’s but the chances are high given the prevalence of the disease.  And just because there’s amyloid in the brain doesn’t mean that other disorders, such as Lewy Body Dementia, aren’t also present.

Amyloid PET scans are slowly moving into clinical use.  Insurance companies generally don’t want to pay for an amyloid PET scan as having a more accurate diagnosis doesn’t presently lead to any helpful treatment.

An interesting study was recently published about how amyloid imaging can change the clinical diagnosis.  The study is discussed here on the AlzForum:

With Amyloid Scan in Hand, Physicians Manage AD Differently
04 Nov 2016

The most interesting part of the study to me was how poor the diagnosis is without using an amyloid PET scan.  The study reported:  (AD = Alzheimer’s Disease)

“PET scans revealed that about one-third of patients diagnosed with AD were amyloid-negative, while about half of patients with other diagnoses were amyloid-positive.”

So this means that about one-third of all the patients neurologists thought had Alzheimer’s don’t have Alzheimer’s.  And half of the patients neurologists thought didn’t have Alzheimer’s in fact have Alzheimer’s!

Did the scan results change the diagnosis?  The study reported:  (Aβ = beta-amyloid)

“Diagnoses for nearly all the Aβ-negative patients changed to non-AD. Only half the non-AD Aβ-positive patients were given a new diagnosis of AD.”

So, the amyloid-negative scans swayed the post-scan diagnosis.  Why did the amyloid-positive scans not change the diagnosis?  AlzForum says:

“Researchers praised the fact that clinicians did not simply equate an amyloid-positive scan with AD. ‘That’s appropriate. The scan should be just one data piece you use along with other clinical context to make a diagnosis,’ [UCSF neurologist Gil] Rabinovici said. He also liked the fact that clinicians put less weight on a positive scan than a negative one, recognizing that amyloid pathology can occur in other disorders. Nevertheless, the 12 amyloid-negative patients maintained their AD diagnosis because they fit the profile of Alzheimer’s extremely well, Boccardi noted. These patients might have had false negative scans, or they might have suspected non-Alzheimer’s pathology (SNAP), she suggested. Analysis of the collected CSF for disease biomarkers might shed additional light on their pathology.”

Clearly, there’s lots more work to do….