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Longitudinal follow up of MCI patients with negative PiB

      Background

      The likelihood of progression from MCI to any form of dementia has been suggested to occur at a rate 3 to 5 times higher than those with normal cognition with an annual rate of progression of 12-20%. MCI patients with negative AD biomarkers are supposed to have a lower risk of dementia related to AD. However they still could suffer from other non-AD etiologies and convert to dementia. The aim is to assess the risk of progression to dementia of Mild Cognitive Impairment (MCI) patients with negative PET PIB for Alzheimer’s Disease (AD).

      Methods

      Thirty-two patients diagnosed with MCI and with negative PET PIB were selected. These patients underwent a complete Neuropsychological battery; brain MRI, PET FDG. Patients were classified into amnestic MCI, multiple domains MCI or non-amnestic MCI. They have been followed up with new neuropsychological testing after AD biomarkers were performed. We considered worsening of MCI status when patients presented worsening of global CDR (conversion to dementia), declination on neuropsychological testing or need to increase anti-dementia medication.

      Results

      Fourteen patients were diagnosed with amnestic MCI, 6 with multiple domains MCI and 12 with non-amnestic MCI. All of them had negative PIB scan and were followed up for 1.6 years. The average age was 68 years old and the average educational level was 16 years. Eight of the 32 patients have worsened their clinical status and seven of them (21.8%) have converted to dementia (CDR 1). Only one of the patients that has converted to dementia was diagnosed with Dementia of Alzheimer type, this one had also PET FDG typical of AD. The rest who have converted to dementia were diagnosed with non-AD dementia (2 Frontotemporal Dementia, 2 vascular dementia, 1 suspected of encephalitis and 1 with psychiatric symptoms).

      Conclusions

      We found in our MCI with negative PIB cohort the same conversion rate to dementia previously documented in MCI patients alone (12-20%). However, those patients who converted to dementia seemed to be due to non-AD dementia. Therefore, we conclude that specialists must be concerned even when PIB scan is negative since patients could have dementia due to other causes.