The usefulness of amyloid imaging in predicting the clinical outcome after two years in subjects with mild cognitive impairment

Background: Mild cognitive impairment (MCI) is a syndrome heterogeneous with regards to etiology and prognosis. Amyloid imaging enables to visualize a hallmark pathology of Alzheimer's disease (AD). Therefore we aimed to assess the usefulness of [¹¹C]PiB PET for predicting clinical outcome of MCI patients after an interval of 2 years. Methods: In 28 MCI participants with a global CDR rating at baseline of 0.5 a baseline examination including clinical assessments and [¹¹C]PiB PET imaging and a clinical follow-up examination after a planned interval of 24 months were performed. Predictive values and accuracy of amyloid-positive and negative scans for conversion to dementia of any type and to dementia due to AD were calculated and compared to neuropsychological tests and ApoE genotyping. Results: Of 17 MCI patients who were amyloid-positive at baseline converted 9 to dementia all of the AD type. 3 of the 11 amyloid-negative MCI subjects converted to dementia but none to dementia due to AD. PPV, NPV and accuracy (to dementia: 0.53, 0.73 and 0.61; to AD: 0.53, 1.00 and 0.70) was comparable to neuropsychological tests and superior to ApoE genotyping. Conclusion: All MCI subjects who converted to dementia due to AD were amyloid-positive. However, only 50% of these MCI due to AD, intermediate likelihood, patients developed manifest dementia due to AD after 24 months limiting the usefulness of [¹¹C]PiB PET for individual prediction of clinical outcome.