123I-FP-CIT striatal binding ratios do not decrease significantly with age in older adults
I-123-2β-Carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl)nortropane (FP-CIT) imaging is an established biomarker used in the diagnosis of Lewy body disease. Images are often reported with the aid of striatal binding ratios (SBRs), comparing uptake to a normal database via Z scores. It is well known that SBRs are age dependent. However, previous studies cover wide age ranges between 20 and 80 years, rather than focusing on older adults. Typically a linear relationship is reported, but some authors have suggested that SBRs do not decline as rapidly in old age. Commercial software packages usually adjust the SBR Z score to attempt to compensate for age-related decline, but the model used varies. Ensuring age correction is appropriate for older adults is important, given that the majority of patients referred for FP-CIT scans are aged over 60 years. We examined the relationship of SBR with age in older adults and the effect of age correction using research scans from 123 adults over 60 years of age.
Twenty-nine healthy older adults and twenty-three with MCI due to Alzheimer’s disease were included as controls, i.e. individuals with no evidence of Lewy body disease. Their ages ranged from 60 to 92 years (mean 76; SD 7.9). SBRs and Z scores were calculated using BRASS (Hermes Medical) and DaTQUANT (GE Healthcare). SBRs were plotted against age and linear mixed effect models applied. We tested the effect of removing age correction in BRASS using an independent dataset of 71 older adults with dementia or mild cognitive impairment.
The slopes of the linear fits between SBR and age per year were − 0.007 (p = 0.30) with BRASS and − 0.004 (p = 0.35) with DaTQUANT. The slopes are smaller than reported in the literature and show no statistically significant difference from zero. Switching age correction off in BRASS in the test subjects reduced Z scores by approximately 1 standard deviation at 80 years of age.
We found no statistically significant age-related decline in SBR in adults over 60 years of age without Lewy body disease. Commercial software packages that apply a fixed rate of age correction may be overcorrecting for age in older adults, which could contribute to misdiagnosis.
KeywordsFP-CIT DaTSCAN SBR Age dependency Lewy body disease
The authors would like to thank Miss Helen Kain, Research Support Secretary (Newcastle University Institute of Neuroscience) and our colleagues in the Nuclear Medicine department at the Newcastle Royal Victoria Infirmary. We thank the Alzheimer’s Society for supporting the Fellowship of the lead author and the NIHR and Alzheimer’s Research UK for supporting the clinical research studies used in this project. We are grateful to Liz Clarke (GE Healthcare) and Helena McMeekin (Hermes Medical) for providing information on DaTQUANT and BRASS, respectively.
The lead author is receiving full-time support from the Alzheimer’s Society via a Clinical Training Fellowship. The clinical studies used in this project were funded by Alzheimer’s Research UK and the Newcastle National Institute for Health Research (NIHR) Biomedical Research Centre, hosted by Newcastle upon Tyne Hospitals NHS Foundation Trust and Newcastle University.
Compliance with ethical standards
Conflict of interest
123I-FP-CIT radiopharmaceutical and the DaTQUANT software package were provided by GE Healthcare. We have no other conflicts of interest relevant to this study.
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