157 WHOLE HIPPOCAMPAL VOLUMES AND HIPPOCAMPAL SUBFIELD VOLUMES IN MCI-LB AND MCI-ad

Background

Mild cognitive impairment with Lewy bodies (MCI-LB) is the commonest prodromal phenotype of Dementia with Lewy Bodies (DLB) and may be challenging to differentiate from MCI due to Alzheimer’s disease (MCI-AD). Preservation of medial temporal lobe structures on MRI is recognised as a supportive biomarker consistent with underlying Lewy body disease rather Alzheimer’s disease (AD).

We investigated whether whole hippocampal volume and differing hippocampal subfield atrophy patterns, could be used as a surrogate biomarker of underlying ad pathology, allowing for differentiation of MCI-LB from MCI-AD.

Methods

Participants were recruited to the following groups’: healthy controls (HC), MCI-LB and MCI-ad, all ≥60 years. Alongside detailed clinical, neuropsychological assessments, all participants underwent 3 T MRI, 123I-FP-CIT SPECT and 123I-MIBG myocardial scintigraphy. Using Freesurfer (v.6.0), a fully automated hippocampal subfield segmentation of the MRI data was performed.

Results

Groups consisted of 31 HC (mean age, 73.7 yrs; mean Mini-Mental state Examination [MMSE] score, 28.4), 34 MCI-LB (mean age, 74.7 yrs; mean MMSE score, 26.6) and 29 MCI-ad (mean age, 75.4 yrs; mean MMSE score, 27.1).

There was no significant difference in whole hippocampal volume between MCI-LB and MCI-ad(Mean (SD) in mm3: MCI-LB 6025 (961) vs MCI-ad 5407 (882), p = 0.12) or between MCI-LB and HC (Mean (SD) in mm3: MCI-LB 6025 (961) vs HC 6355 (962), p = 0.11). Whole hippocampal volume was significantly smaller in MCI-ad compared with HC (p < 0.001).

Comparison between MCI-LB and MCI-ad, showed absolute hippocampal subfield volumes were all lower in MCI-ad. However, the magnitude of the differences were small and no significant difference in hippocampal subfield volumes were noted between these groups, with the exception of the hippocampal tail being significantly smaller in MCI-ad compared to MCI-LB (p = 0.04).

Conclusion

In a well-characterised cohort, whole hippocampal and hippocampal subfield volumes were similarly atrophied in MCI-LB and MCI-ad and did not distinguish between the groups.

Alpha4beta2 nicotinic receptor status in Alzheimer's disease using 123I-5IA-85380 single-photon-emission computed tomography

BACKGROUND

Loss of the alpha4beta2 nicotinic receptor subtype is found at autopsy in Alzheimer's disease.

OBJECTIVE

To investigate in vivo changes in this receptor using single-photon-emission CT (SPECT) with 123I-5-iodo-3-[2(S)-2-azetidinylmethoxy] pyridine (5IA-85380), a novel nicotinic acetylcholine receptor ligand which binds predominantly to the alpha4beta2 receptor.

METHODS

32 non-smoking subjects (16 with Alzheimer's disease and 16 normal elderly controls) underwent 123I-5IA-85380 and perfusion (99mTc-hexamethylenepropyleneamine oxime (HMPAO)) SPECT scanning. Region of interest analysis was performed with cerebellar normalisation.

RESULTS

Significant bilateral reductions in nicotinic receptor binding were identified in frontal (left, p = 0.004; right, p = 0.002), striatal (left, p = 0.004; right, p = 0.003), right medial temporal (p = 0.04) and pons (p<0.001) in patients with AD compared to controls. There were no significant correlations with clinical or cognitive measures. The pattern of nicotinic binding significantly differed from that of perfusion in both patients with AD and controls. Both 123I-5IA-85380 and 99mTc-HMPAO SPECT imaging demonstrated similar diagnostic performance in correctly classifying controls and patients with AD.

CONCLUSION

Using 123I-5IA-85380 SPECT we found changes consistent with significant reductions in the nicotinic alpha4beta2 receptor in cortical and striatal brain regions. This method could facilitate diagnosis and may be useful for monitoring progression of the disease and response to treatment in patients with AD and related diseases.

Verbal instructions and top-down saccade control

Few studies have addressed the interaction between instruction content and saccadic eye movement control. To assess the impact of instructions on top-down control, we instructed 20 healthy volunteers to deliberately delay saccade triggering, to make inaccurate saccades or to redirect saccades--i.e. to glimpse towards and then immediately opposite to the target. Regular pro- and antisaccade tasks were used for comparison. Bottom-up visual input remained unchanged and was a gap paradigm for all instructions. In the inaccuracy and delay tasks, both latencies and accuracies were detrimentally impaired by either type of instruction and the variability of latency and accuracy was increased. The intersaccadic interval (ISI) required to correct erroneous antisaccades was shorter than the ISI for instructed direction changes in the redirection task. The word-by-word instruction content interferes with top-down saccade control. Top-down control is a time consuming process, which may override bottom-up processing only during a limited time period. It is questionable whether parallel processing is possible in top-down control, since the long ISI for instructed direction changes suggests sequential planning.

Regional cerebral blood flow in Parkinson's disease with and without dementia

Tc99 HMPAO SPECT and T1 weighted 3D MRI scans were acquired in cognitively intact subjects with Parkinson's disease (PD) (n = 31), and in PD subjects with dementia (PDD) (n = 34), healthy controls (n = 37), those with Alzheimer's disease (AD) (n = 32), and those with dementia with Lewy bodies (DLB) (n = 15). We used SPM99 to look for regions which showed a reduction in perfusion on SPECT not related to associated structural brain changes assessed by a MRI scan. The precuneus and inferior lateral parietal regions showed a perfusion deficit in Parkinson's disease with dementia, similar to the pattern observed in DLB. In comparison, AD showed a perfusion deficit in the midline parietal region, in a more anterior and inferior location than in PDD, involving the posterior cingulate as well as the precuneus. The perfusion deficits in PDD are similar those in DLB, and in a location associated with visual processing, and may be associated with the visuospatial perception deficits which are present in persons with DLB and PDD.