The patient was a 55-year-old right-handed white man with DS and 8 years of formal education through special education. At the time of presentation at age 51 years, the patient was having difficulty maintaining occupational duties at his job at a gas station, difficulty multitasking, confusion with well-known tasks, word and naming difficulty, and a loss of pleasurable activities. He was having difficulty with doing his own cooking and maintaining his home environment. He also had become less fastidious regarding appearance. He had no change in his personality or mood, no weight loss, no reported hallucinations or delusions, and no change in gait or posture.
The patient’s medical history at initial presentation included DS, cataracts, and gout, with no remarkable surgical history except for cataract extraction or medical allergies. The patient’s medications included allopurinol and mouthwash for stomatitis. His family history indicated risk for diabetes mellitus, hypertension, and coronary disease, as well as a mother who died with AD. The patient’s social history was unremarkable. He resided in a group home. The patient was not reported to have incontinence. The review of systems was not significant for notable change in appetite, weight, or sleep and was not indicative of anxiety or depression.
The patient’s physical examination at initial evaluation revealed normal vital signs, including regular cardiovascular rate and rhythm as well as normotensive blood pressure. He exhibited a rash on his scalp and morphologic features consistent with a diagnosis of DS.
His neurologic examination revealed intact cranial nerves. His motor examination indicated normality in all muscle groups. The patient exhibited intact sensation peripherally and intact coordination and stood toe to heel in tandem. The patient’s deep tendon reflexes were symmetric and brisk throughout.
The patient’s initial cognitive examination indicated that his mentation was alert and his speech fluent. His premorbid IQ was difficult to gauge, but his medical records indicated that neuropsychologic testing performed 11 years before presentation put his full-scale IQ at 55, his verbal IQ at 53, and his performance IQ at 63, which are all consistent with mild retardation. His Mini-Mental State Examination11
score at the time of the initial neurologic evaluation for cognitive decline was derived and ascertained to be approximately 11/23. During the next few years, he declined in terms of cognitive ability and developed agitation and aggressive behavior. He was treated with Aricept (donepezil hydrochloride; Pfizer Inc), Namenda (memantine hydrochloride; Forest), and antidepressant and antipsychotic medications. In 2006, he had a seizure (not described in detail). Beginning in September 2007, he was noted to have a slow shuffling gait, and later his posture also became stooped. In the last year of life, he had visual hallucinations and multiple falls, as well as myoclonic jerking and tremors. He was using a wheelchair. Carbidopa-levodopa was added to his treatment regimen. A magnetic resonance imaging scan performed in March 2009 showed enlarged lateral ventricles and dystrophic calcifications of the head of the caudate nucleus and globus pallidus. The patient progressively declined in a manner typical of AD during the 4 years ensuing from the low initial assessment baseline until he was nontestable, with his last Mini-Mental State Examination score recorded as 0. The patient was enrolled in a florbetapir histopathology study.
FLORBETAPIR IMAGING METHODS
The patient received a 10-minute florbetapir positron emission tomography (PET) scan, beginning 50 minutes after a single intravenous bolus of 370 MBq (10 mCi) F-18 florbetapir. Images were acquired with a 128×128 matrix (zoom 2) and were reconstructed with an iterative reconstruction algorithm. Images were assessed using a semiquantitative visual image score ranging from 0 (no cortical amyloid) to 4 (high levels of amyloid).10
Three independent readers, masked to all clinical, demographic, and neuropathologic information, performed the visual rating. The median rating of these 3 readers served as the primary outcome variable. Independently, the images were first normalized to a standard template in Talairach space (SPM2, http://www.fil.ion.ucl.ac.uk/spm/
), and then a semiautomated algorithm was used to calculate standard uptake value ratios (SUVRs) in predefined anatomically relevant cortical regions (frontal, temporal, parietal, anterior cingulate, posterior cingulate, and precuneus), with the whole cerebellum as the reference region.
To explore the Aβ deposition pattern, voxel-wise SUVRs (parametric imaging) were generated using the same reference region. The patient died 14 days after imaging. The brain was collected at autopsy for neuropathologic analysis. Neuropathologic studies were performed without knowledge of the clinical and PET data.
At the time of death, the brain was removed and processed according to the standard autopsy protocol for the Avid A07 clinical trial (NCT00857415). The brain was placed in fixative for 2 weeks before dissection at Banner Sun Health Research Institute, Sun City, Arizona.
Three independent methods were used to identify and to quantify cerebral amyloid burden. The first method used immunohistochemistry with Aβ antibody 4G8 (1:2000 dilution; antibody localization was amplified with an avidinbiotin peroxidase [VECTASTAIN Elite ABC System; Vector Laboratories, Inc, Burlingame, CA] and visualized with 3,3′-diaminobenzidine enhanced with a mixture of nickel and ammonium sulfate as horseradish peroxidase substrate [Signet, Dedham, Massachusetts; provided by Covance, Princeton, New Jersey]) at Biospective Inc, Montreal, Canada. The stained slides were digitized using a Zeiss MIRAX high-resolution automated slide scanner (Carl Zeiss Canada, Toronto, Ontario). Image quantification was performed using the PERMITS image processing/analysis software (Biospective Inc). This automated quantification method segments chromogen-positive pixels based on red-green-blue intensity and generates a parametric map of Aβ aggregation over the entire tissue section. The Aβ burden (percentage of gray matter containing Aβ aggregates) was calculated for each tissue section and averaged across multiple slides for each anatomical region.
The second method used a modified Bielchowsky silver stain applied to 6-μm sections cut from each region of interest and cerebellum. Two sections, separated by 300 μm, were evaluated from each region, and the average was used to represent the plaque density. Density of both neuritic and diffuse plaques was assessed by 2 independent experienced neuropathology raters using the Consortium to Establish a Registry for Alzheimer’s Disease templates. The results were reviewed by a senior neuropathologist (T.G.B.); all were masked to the clinical information and imaging results.
The third method of estimating plaque burden was that used as a standard protocol at the Banner Sun Health Research Institute Brain and Body Donation Program. Standardized fixed and cryoprotected 4×5-cm tissue blocks were sectioned at 40μm on a sliding freezing micro tome, and sections were stained using the Campbell-Switzer Gallyas silver stains. 12
Average total (neuritic and diffuse) plaque densities as well as average neuro fibrillary tangle densities were estimated using the Consortium to Establish a Registry for Alzheimer’s Disease templates as zero, sparse, moderate, or frequent in the following regions: frontal lobe cortex at the coronal level of the genu of the corpus callosum, temporal lobe cortex at the coronal level of the amygdala and at the level of the lateral geniculate nucleus, and parietal lobe cortex at a level 1-cm caudal to the splenium of the corpus callosum. Density descriptive terms were converted to a 0-to-4 scale for statistical purposes. Braak neuro fibrillary tangle stage was established according to the original publication.10
The DS patient’s florbetapir PET image (analyzed both in terms of raw counts and cerebral-to-whole cerebellar SUVRs) revealed a pattern of cortical fibrillar amyloid burden similar to that in patients with late-onset AD (). All 6 cortical regions evaluated demonstrated significant cortical florbetapir uptake in both visual reads and SUVR analysis (). The image also revealed fibrillar amyloid burden in the striatum and thalamus. On visual inspection, there was also more tracer uptake in the cerebellum than typically seen.13
However, whole cerebellar uptake quantitated within the normal range, resulting in cortical-to-whole cerebellar SUVRs in the expected range for florbetapir.13
Figure 1 Florbetapir F18 positron emission tomography (PET) images of fibrillar amyloid-β (Aβ) burden in an end-of-life, neuropathologically verified patient with Down syndrome and Alzheimer disease. A, Sagittal, coronal, and horizontal brain sections (more ...)
Figure 2 Diffuse amyloid plaques, neuritic plaques, and percentage of cortical amyloid on immunohistochemistry on pathology were elevated in all 6 regions assessed. Amyloid pathology was consistent with regional quantitative florbetapir standard uptake value ratios (more ...)
On gross examination, the anterior part of the temporall obes showed gyral atrophy with no herniation, as well as marked atrophy of the amygdala, head and body of the hippocampus, and parahippocampal gyrus.4
The cerebellum and brainstem were externally unremarkable. Cerebral slices revealed no cortical lesions but moderate to marked dilation of the lateral and third ventricles. Histology with hematoxylin-eosin showed substantial gliosis of the upper neocortical layers, with many Aβ plaques and neurofibrillary tangles.2
Mild depigmentation of the substantia nigra, without Lewy bodies, and calcification of the basal ganglia were observed; the latter is common in DS. Otherwise, sections of the basal ganglia, thalamus, subthalamic regions, cerebellum, brainstem, spinal cord, and paraspinal sympathetic ganglia were unremarkable. Amyloid staining revealed frequent diffuse, neuritic, and cored Aβ plaques and frequent neurofibrillary tangles in neocortex and limbic areas (). The Braak stage was VI. Diffuse Aβ plaques were observed in the cerebellum, striatum, and thalamus, with frequent amyloidotic blood vessels in all cerebral lobes, thalamus, striatum, and cerebellum. Immunohistochemical staining for phosphorylated α-synuclein showed no evidence of neuronal cytoplasmic inclusions or neurites in multiple sections of the olfactory bulb, brainstem, amygdala, cerebral cortex, spinal cord, or paraspinal sympathetic ganglia. The final neuropathologic diagnosis, based on established National Institutes of Health Alzheimer Disease Center criteria,14
was AD with trisomy 21.
Figure 3 Sections of cerebral cortex regions stained for amyloid with the Campbell-Switzer Gallyas stain, revealing frequent diffuse, neuritic, and cored amyloid plaques throughout the cerebral cortex. A, Middle frontal gyrus. B, Anterior cingulate gyrus. C, Middle (more ...)
COMPARISON OF FLORBETAPIR AND AUTOPSY FINDINGS
Diffuse amyloid plaques, neuritic plaques, and percentage of cortical amyloid on immunohistochemistry on pathology were elevated in all 6 regions assessed (). Amyloid pathologic features were consistent with regional quantitative florbetapir SUVRs and visual reads ().