The degeneration of locus coeruleus occurring during Alzheimer’s disease clinical progression: a neuroimaging follow-up investigation

The noradrenergic nucleus Locus Coeruleus (LC) is precociously involved in Alzheimer’s Disease (AD) pathology, and its degeneration progresses during the course of the disease. Using Magnetic Resonance Imaging (MRI), researchers showed also in vivo in patients the disruption of LC, which can be observed both in Mild Cognitively Impaired individuals and AD demented patients. In this study, we report the results of a follow-up neuroradiological assessment, in which we evaluated the LC degeneration overtime in a group of cognitively impaired patients, submitted to MRI both at baseline and at the end of a 2.5-year follow-up. We found that a progressive LC disruption can be observed also in vivo, involving the entire nucleus and associated with clinical diagnosis. Our findings parallel neuropathological ones, which showed a continuous increase of neuronal death and volumetric atrophy within the LC with the progression of Braak’s stages for neurofibrillary pathology. This supports the reliability of MRI as a tool for exploring the integrity of the central noradrenergic system in neurodegenerative disorders. Supplementary Information The online version contains supplementary material available at 10.1007/s00429-024-02797-1.


Supplementary Methods & Results S1
From the paper "The degeneration of Locus Coeruleus occurring during Alzheimer's Disease clinical progression: a neuroimaging follow-up investigation" published on "Brain Structure and Function" by Alessandro Galgani. Francesco Lombardo. Francesca Frija. Nicola Martini. Gloria Tognoni. Nicola Pavese and Filippo S. Giorgi*. (*Corresponding author: Department of Translational Research and of New Surgical and Medical Technologies. University of Pisa. e-mail address: filippo.giorgi@unipi.it).

Patients selection and inclusion
Patients were recruited at the Neurological Unit of Pisa University Hospital.During the baseline visit, they underwent a comprehensive neurological and neuropsychological evaluation to exclude the occurrence of other neurological disorders and assess the severity of cognitive decline.The Clinical Dementia Rating scale (CDR) (Hughes et al. 1982) and Mini-Mental State Examination (Folstein et al. 1975) were used as measures of global functioning and cognition, respectively.MCI subjects were required to score CDR<1 at T0, and only mild ADD patients were included (CDR<2).A trained and certified rater performed the neuropsychological assessment, exploring the following domains: a) working memory and executive function; b) memory; c) processing speed and attention.The specific tests used were: a) Digit Span (Orsini et al. 1987), Corsi Block Span (Orsini et al. 1987), Phonemic Fluency Test (controlled oral word fluency to the letters F-A-S) (Carlesimo et al. 1996), Stroop test (Caffarra et al. 2002), and Trail Making Test (TMT) subitem B-A (Giovagnoli et al. 1996); b) Rey Auditory Verbal Learning Test (RAVLT) (Carlesimo et al. 1996), Free and Cued Selective Reminding Test (FCSRT) (Girtler et al. 2015), and Rey-Osterrieth Complex Figure Test (Carlesimo et al. 2002); c) TMT subitem A (Giovagnoli et al. 1996) and Digit Symbol Substitution Test (Lang et al. 2013).Amnestic (or hippocampal) syndrome was identified based on the pathological results for both RAVLT and FCSRT, following current research diagnostic criteria (Carlesimo et al. 1996;Albert et al. 2011;Girtler et al. 2015).
Upon the execution of Brain 3T MRI, we ruled out the occurrence of severe ischemic encephalopathy (Fazekas modified scale score > 2 (Fazekas et al. 1987)) or other intra/extra-parenchymal pathologies; furthermore, we strengthened the clinical diagnosis based on cortical atrophy maps (see Results section of this S1).Other exclusion criteria included severe cardiac or psychiatric comorbidities, alcohol and/or substance abuse, and severe hepatic/renal/metabolic/endocrine diseases.

Voxel-based morphometry and hippocampal volume
For voxel-based morphometry (VBM) analysis the data were analyzed with an optimized VBM protocol (Good et al. 2001)carried out with FSL tools (http://fsl.fmrib.ox.ac.uk/fsl).The structural images were segmented and registered to the 2mm MNI 152 standard space to create a study-specific grey matter template.Then all our GM images were non-linearly register to the study-specific template and concatenate them into a 4D image.A design matrix for a general linear model was constructed FSL to compare grey matter differences between two-group (accounting age as a nuisance covariate).TFCE-based (Threshold-Free Cluster Enhancement) analysis was applied with 10000 permutations, family-wise error rate (FWE) was controlled and FWE-corrected p-values less than 0.05 were accepted.For the hippocampal volume analysis method, we defined the masks based on Harvard-Oxford Cortical Structural atlas.GM volumes of the left and right hippocampus were extracted for each mask and for each patient from the 4D image, and then standardized for the total intracranial volume (TIV).

Cortical morphometry and hippocampal volume
In the VBM analysis, we found that the cortical volume of the bilateral superior frontal gyri and of the middle and lower left frontal gyri were lower ADD group when compared to cMCI, but this did not reach the statistical significance (p<0,1) (Supplem.Figure 1).On the other hand, when we compared the ADD with the ncMCI group, the volume of several cortical areas was significantly lower than in the former group (p<0.01)(Supp.Figure 1).No difference was found comparing the cMCI and ncMCI groups (Supplem.Figure 1).Baseline hippocampal volume was not different among diagnostic groups (See Supplem. Table 2).A significant reduction of hippocampal volume was found both in all subjects (p=0.015 for the right hippocampus and p=0.003 for the left one) and in cMCI (p=0.011 and p=0.027 for the right and left hippocampus, respectively).At the follow-up assessment, both cMCI and ADD showed lower hippocampal volume than ncMCI, both in the right (p=0.002 and p=0.007, respectively) and in the left (p=0.001and p=0.042, respectively) hippocampus (Supplem.Table 1).