[(123)]FP-CIT SPECT scans initially rated as normal became abnormal over time in patients with probable dementia with Lewy bodies

Abstract

Purpose: Decreased striatal dopamine transporter (DAT) binding on SPECT imaging is a strong biomarker for the diagnosis of dementia with Lewy bodies (DLB). There is still a lot of uncertainty about patients meeting the clinical criteria for probable DLB who have a normal DAT SPECT scan (DLB/S-). The aim of this study was to describe the clinical and imaging follow-up in these patients, and compare them to DLB patients with abnormal baseline scans (DLB/S+).

Methods: DLB patients who underwent DAT imaging ([(123)I]FP-CIT SPECT) were selected from the Amsterdam Dementia Cohort. All [(123)I]FP-CIT SPECT scans were evaluated independently by two nuclear medicine physicians and in patients with normal scans follow-up imaging was obtained. We matched DLB/S-- patients for age and disease duration to DLB/S+ patients and compared their clinical characteristics.

Results: Of 67 [(123)I]FP-CIT SPECT scans, 7 (10.4 %) were rated as normal. In five DLB/S- patients, a second [(123)I]FP-CIT SPECT was performed (after on average 1.5 years) and these scans were all abnormal. No significant differences in clinical characteristics were found at baseline. DLB/S- patients could be expected to have a better MMSE score after 1 year.

Conclusion: This study was the first to investigate DLB patients with the initial [(123)I]FP-CIT SPECT scan rated as normal and subsequent scans during disease progression rated as abnormal. We hypothesize that DLB/S- scans could represent a relatively rare DLB subtype with possibly a different severity or spread of alpha-synuclein pathology ("neocortical predominant subtype"). In clinical practice, if an alternative diagnosis is not imminent in a DLB/S- patient, repeating [(123)I]FP-CIT SPECT should be considered.

Keywords: Dementia with Lewy bodies; Dopamine transporter; Neuroimaging; [123I]FP-CIT SPECT.

Fig. 1

Upper panel: [¹²³I]FP-CIT SPECT scan (transverse slices) acquired in 2011 (binding ratios: right caudate nucleus 2.62, left caudate nucleus 2.56, right putamen 2.37, and left putamen 2.21). Lower panel: follow-up [¹²³I]FP-CIT SPECT scan acquired in 2012 shows lower tracer binding (binding ratios: 1.82, 1.84, 1.95, and 1.70, respectively)

Fig. 2

Tracer binding ratios in four regions of interest in five DLB patients with an initially normal [¹²³I]FP-CIT SPECT scan (blue). The binding ratios are lower on the second [¹²³I]FP-CIT SPECT scan (green)