Review question: In people with mild cognitive impairment (MCI), does using a ¹⁸F PET scan with flutemetamol predict the progression to Alzheimer’s disease dementia (ADD) and other dementias?

Background

Due to global ageing, the number of people with dementia is expected to increase dramatically in the next few decades. Diagnosing dementia at an early stage is desirable, but there is no widespread agreement on the best approach. A range of simple pen and paper tests used by healthcare professionals can assess people with poor memory or cognitive impairment. Whether or not using special PET scans that detect amyloid —one of the hallmarks of Alzheimer’s disease— improves our ability to predict the progression from MCI to ADD or other forms of dementia remains unclear. Since these tests are expensive, it is important that they provide additional benefits.

Aim

We aimed to evaluate the accuracy of the ¹⁸F-flutemetamol PET scan in identifying those people with MCI who clinically progress to ADD, other types of dementia, or any form of dementia over a period of time.

Study characteristics

The evidence is current to May 2017. We found two studies evaluating the progression from MCI to ADD. The studies included 252 MCI eligible participants, with 243 participants that had follow-up. Of these, 127 were women. The average age in one study with two years of follow-up was 72.7 + 7.09 years. In the other study with three years of follow-up, the average age was 71.1 + 8.62 years. The setting in one study was memory clinics.

Study funding sources: both studies were funded by the test manufacturer.

Quality of the evidence

The main limitation of this review was that our findings were based on only two studies, with not enough details on how the people were selected, how the interpretation of the PET scan was made in one study, how the clinical diagnosis of dementia was established in the other study. The studies were considered to be at high risk of bias due to potential conflicts of interest detected.

Key findings

In this review, we found that the ¹⁸F-flutemetamol PET scan, as a single test, in one study with 19 participants included with 2 years of follow-up, had a sensitivity of 89% and a specificity of 80%. This means that in a cohort with 100 participants with MCI and a proportion of progression in this study of 47%, we would expect 42 of 47 MCI participants with a positive result for ¹⁸F-flutemetamol scan to progress to ADD, and 5 participants to be falsely positive. In addition, we would expect 42 of 53 participants who will not progress to ADD to have a negative result for ¹⁸F-flutemetamol, and 11 to be falsely negative.

In the other study with 224 participants included in the analysis with 3 years follow-up, the sensitivity was 64% and the specificity was 69%. This means that in a cohort with 100 participants with MCI and a proportion of progression in this study of 36%, we would expect 23 of 36 MCI participants with a positive result for ¹⁸F-flutemetamol to progress to ADD, and 13 participants to be falsely positive. In addition, we would expect 44 of 64 participants who will not progress to ADD to have a negative result for ¹⁸F-flutemetamol, and 20 to be falsely negative.

There was no information regarding the progression from MCI to other forms of dementia and progression to any form of dementia at follow-up.

We conclude that ¹⁸F-flutemetamol PET imaging cannot be recommended for routine use in clinical practice to predict the progression from MCI to ADD based on the currently available data. More studies are needed to clearly demonstrate its usefulness.