New Brain Imaging for Alzheimer’s Disease

Amyloid proteins in normal brains (left) and abnormal ones (right) visualized with GE Healthcare’s PET tracer flutemetamol.

Alzheimer’s disease is the commonest cause of dementia, and as the population is aging, it’s prevalence is increasing.

Alzheimer’s disease presently affects 5 million Americans aged 65 or older.  Without a major medical breakthrough, by 2025 this number is expected to have risen to 7 million, and by 2050 it could reach 14 million

The costs of caring for Alzheimer’s patients is also increasing, estimated at $203 billion in 2013, and $1.2 trillion by 2050,  including a 500% increase in combined Medicare and Medicaid spending.

Clearly, finding that major therapeutic breakthrough is crucial, and had been identified as a priority by the Obama Administration.

The first barrier to starting any clinical trial is accurate case ascertainment – we have to be able to correctly identify early Alzheimer’s patients for new experimental treatments.

So far, the only definitive test for Alzheimer’s disease is examination of brain tissue (usually obtained at autopsy) for identification of the characteristic pathologic changes of Amyloid paque and Neurofibrillary tangles:

Alzheimer’s disease is usually diagnosed based on  clinical criteria, but many patients diagnosed this way are later found to have other causes of dementia when their brains are examined at autopsy, in other words they were misdiagnosed as Alzheimer’s.

With more research trials and potential new effective therapies on the horizon, it is going to become more important to establish a diagnosis of Alzheimer’s more accurately and earlier, perhaps even pre-symptomatically (i.e. mild cognitive impairment or MCI), so that treatment to reverse the build up of plaque and tangles is more likely to be effective.

New positron emission tomography (PET) technology can actually quantify the amount of amyloid in affected patients’ brains.  A recently published small study showed a very high correlation between amyloid identified on PET scans and amyloid plaque demonstrated in brain biopsy specimens taken from demented patients.

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These tests are going to be very important for research studies.

However, don’t rush to your private doctor’s office asking to have one done just yet!

Although approved by the FDA, these test are not yet covered by Medicare or other insurance covering, and cost between $1500 and $3000.

Furthermore, these are new tests, and their role in clinical neurology practice in still unclear.

Some of these issues were recently clarified in a report by the Amyloid Imaging Taskforce convened by the Alzheimer’s Association and the Society of Nuclear Medicine and Molecular Imaging:

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This taskforce concluded that a Amyloid PET scan is indicated for:

Progressive memory impairment or dementia with atypical features, where a positive PET would indicate definite Alzheimer’s, and a negative scan would rule it out and lead to further testing for other possible causes.

Younger patients (aged 50-65) with suspected Alzheimer’s, in whom making a definitive diagnosis is crucial for log term planning and future medical decision making.

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The taskforce concluded that a Amyloid PET scan is unnecessary and/or unhelpful for:

Patients with typical Alzheimer’s disease,

Determining the severity of dementia,

Asymptomatic patients with a family history of dementia or positive apolipoprotein E4 status,

Patients who complain of memory loss but have no objective findings,

Testing purely for medico-legal, disability, insurance or employment related issues.

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Find out more:

Click here to find out more about Memory loss, Mild Cognitive Impairment and Alzheimer’s.

Click here to find out more about diagnosing Alzheimer’s.

Links to the Alzheimer’s Association, Alzheimer’s Foundation of America and CDC Healthy Brain Initiative

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Prions: Could these zombie-like proteins be responsible for causing the most common form of Dementia?

Post courtesy of Dr Michael Chan, PGY2 Medicine Resident, Monmouth Medical Center.

ImageAs far as infectious diseases go, prions are a relatively new discovery. While humanity has known about parasites since ancient times, bacteria since the 1660s, and viruses since 1898, the first prion protein was only isolated in 1984. Since then, we’ve gotten to know a little more about these proteins, and we’ve found that its novelty is by no means the most interesting thing about it.
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So what are prions?

Prions are basically the misfolded version of a normal protein, PRP or Protease resistant protein. In the vast majority of instances, the body has mechanisms that adequately deal with misshapen proteins. These get tagged for destruction by antibodies or intracellularly by specific molecular signals and lysosomes. However, prions are not your run of the mill abnormal protein. They are resistant to degradation and exhibit the unique characteristic of causing other normal PRP proteins to misfold, which in turn causes even more misfolding. In this sense, prions behave like protein zombies.

And like zombies, they don’t begin their existence as malevolent molecules either. Indeed this is one of the characteristics which differentiate prions from most other infectious agents such as bacteria or viruses, majority of which are inherently disease causing. Studies have shown that normal PRP has functions in sleep, memory, neural development, and possibly the maintenance of the myelin sheath that surrounds neurons. Indeed, a mutation of PRP causes a very rare disease (only 8 cases have been diagnosed as of 2005) called Familial Fatal Insomnia which leads to progressively worse insomnia leading to dementia, hallucinations, and eventually death.

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Yes, complete inability to sleep kills.


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The connection to Alzheimer’s

Until recently, the most notable examples of prion diseases in humans are Creutzfeldt-Jakob disease and Kuru. Although spontaneous CJD does rarely occur, both these diseases are usually caused by ingestion of infected material, ie, eating infected meat (beef) for CJD and cannibalism for Kuru. Both exhibit progressive dementia, memory problems, gait and movement disturbances, and other unusual symptoms like uncontrolled laughter, hallucinations, and personality changes. Pathologically, the disease causes patients’ brains to develop tiny holes, much like a sponge. Thus the name for the disease in cows, Bovine Spongiform Encephalopathy, literally translates “cow spongy brain disease”.

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Brain of a CJD patient with multiple “holes”

However, over the past 5 years, research has shown that at least one major protein known to accumulate in Alzheimers disease, amyloid beta, behaves much like prions. Research conducted at UCSF showed that when mice brains are seeded with amyloid beta, after 300 days, the amyloid plaque is found all over the brain, not just the area seeded. A Yale university study in 2009 also showed that prion proteins of CJD interact with amyloid beta in some way to cause the dysfunction in neurons which lead to Alzheimer’s. Although there is no evidence that AD is contagious, it may open up new therapeutic avenues to think of its pathology as like that of prion diseases.

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Amyloid plaques and Neurofibrillary tangles in Alzheimer’s disease

How Alzheimer’s spreads in the brain.

Indeed, last year, a British team accidentally stumbled on a discovery that antibodies designed to treat CJD were found to block Alzheimer’s disease. These antibodies, ICSM-35 and ICSM-18, blocked the interaction between the PRP prion and amyloid beta in mice brains, resulting in decreased hippocampal nerve cell disruption. ICSM-18 and ICSM-35 are presently undergoing human trials for the treatment of CJD. With this finding, it’s likely they will be tested for Alzheimer’s as well, and we, for the first time, might have an effective and specific treatment for this disease which affects roughly 20 million people worldwide.

To see just how significant any form of treatment might be, check out the facts and figures provided by http://www.alz.org below:

References:

Jucker M, Walker LC. Pathogenic protein seeding in Alzheimer disease and other neurodegenerative disorders. 2011:70, 532–540.

Prusiner SB: A unifying role for prions in neurodegenerative diseases. 2012:336, 1511–1513.

Freir DB, Nicoll AJ, Klyubin I et alInteraction between prion protein and toxic amyloid β assemblies can be therapeutically targeted at multiple sitesNature Communications, June 7 2011

Cortical Basal Ganglionic Degeneration

This post is provided courtesy of K. T. Weber, Drexel University College of Medicine Class of 2013:

Cortical Basal Ganglionic Degeneration (CBGD) is a rare neurodegenerative disorder that affects both the cerebral cortex and basal ganglia, resulting in a rapidly progressive and devastating combination of movement disorder and dementia.

CBGD shares features with other, more common, neurologic illnesses: Like Parkinson’s disease, it often presents asymmetrically, with a tremor, rigidity or dystonia. Like Alzheimer’s disease, there are subtle early cognitive and behavioral changes. However, CBGD progresses more rapidly than these other conditions, ultimately involving the other limbs and causing more cognitive dysfunction. Furthermore the Parkinsonian features of CBGD tend not to respond to dopaminergic medications.

Patient with CBGD, showing rigidity, paucity of movement, and myoclonic jerks in the left arm

One of the distinctive features of CBGD is alien limb phenomenon. Alien limb is characterized by a “loss of agency” in the affected limb. The patient is able to feel sensation in the limb, and movement is preserved, but the patient no longer recognizes the limb as his or her own. This same aLien limb or (more commonly an alien hand) syndrome can also result from separation or dysregulation between the brain’s hemispheres, for example after surgical division of the corpus callosum for severe epilepsy.

Patient with CBGD, showing rigidity, dystonic posturing and Alien limb phenomenon (the patient said the left arm was “moving on it’s own”)

In popular media, Dr. Strangelove struggled with an alien limb that was no longer under his control.

However, the movement disorder is only half the story, and symptoms also include behavioral changes, cognitive decline, and abnormal speech. Behavioral changes may involve personality changes, mood problems, like depression and agitation, or the development of new compulsive behaviors. Language problems often begin with difficulty finding words (“anomia“) and may progress to an inability to speak.

The disorder is currently classified as a “tauopathy” in the same family of diseases as Pick’s disease, progressive supranuclear palsy (PSP), and even Alzheimer’s disease.

Although the diagnosis of CBGD is mostly clinical, there are some diagnostic tests that may helpful, such as asymmetric cortical atrophy on brain imaging or asymmetric slowing on EEG.

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MRI showing right hemispheric atrophy

EEG showing L hemispheric slowing

EEG showing R hemispheric slowing

However, a definitive diagnosis can only be made by examining brain tissue at autopsy.

Pathology of CBGD (A) In the neocortex, ballooned neurons with displaced nuclei and pale cytoplasm (arrow) are common. (B) Immunostaining detects diffuse accumulations of tau protein in a peripheral distribution in a ballooned neuron. (C) Neuron loss and gliosis are often severe in deep nuclei, including the substantia nigra. (D) Diffuse cytoplasmic accumulation of tau protein is seen in neurons of various sizes in the neocortex (arrow, panel D), nucleus basalis (E) and striatum (F), as well as other locations. (Panels A,C from sections stained with H and E, remaining panels from sections immunostained with primary antibodies to tau).

Pathology of CBGD (A) In the neocortex, ballooned neurons with displaced nuclei and pale cytoplasm (arrow) are common. (B) Immunostaining detects diffuse accumulations of tau protein in a peripheral distribution in a ballooned neuron. (C) Neuron loss and gliosis are often severe in deep nuclei, including the substantia nigra. (D) Diffuse cytoplasmic accumulation of tau protein is seen in neurons of various sizes in the neocortex (arrow, panel D), nucleus basalis (E) and striatum (F), as well as other locations. (Panels A,C from sections stained with H and E, remaining panels from sections immunostained with primary antibodies to tau).

There are no effective treatments for CBGD, and therapy is aimed at symptomatic relief. The movement disorder, unlike Parkinson’s disease, does NOT respond well to levadopa, so other medications are used to help control the tremors and stiffness in the limbs. Beta blockers (propanolol), benzodiazepines (clonazepam), and gabapentin may have some efficacy in controlling tremor. Baclofen (a GABA agonist) is used to treat spasticity of many different causes and may provide some relief to patients with CBGD. Additionally, the depression, anxiety and agitation due to degeneration the cortical areas of the brain are critical therapeutic targets, and often respond to the first line therapies, including SSRIs and other antidepressants.

In summary, CBGD is a rare, progressive neurodegenerative disease. Recognizing the constellation of symptoms of CBGD from its more common cousins helps patients by identifying all elements of the disease progression, and can improve quality of life by addressing each of the related symptoms.

Diagnostic testing for Alzheimer’s?

The only definitive test for Alzheimer’s disease is examination of brain tissue (usually obtained at autopsy) for identification of the characteristic pathologic changes of Amyloid paque and Neurofibrillary tangles:
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Alzheimer’s disease is usually diagnosed based on  clinical criteria, but many patients diagnosed this way are later found to have other causes of dementia when their brains are examined at autopsy, in other words they were misdiagnosed as Alzheimer’s.

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With more effective new therapies on the horizon, it is going to become more important to establish a diagnosis of Alzheimer’s more accurately and earlier, perhaps even pre-symptomatically (i.e. mild cognitive impairment or MCI), so that treatment to reverse the build up of plaque and tangles is more likely to be effective.

There has been interest in Apoprotein E (APOE) genotype and Alzheimer’s risk. APOE genes come in 3 types (2-4).  If you have 2 copies of  APOE4 (1-2% of the population)  you are 15 times more likely to develop Alzheimer’s than averages, and if you have one copy of APOE4 you have are 3 times more likely to develop Alzheimer’s than average.   Clearly, there is an association between APOE4 genoytpe and Alzheimer’s.  However, not every patient with APOE4 develops Alzheimer’s, and you can develop Alzheimer’s without APOE4, so APOE genotyping is not recommended as a diagnostic test.

The ratio of cerebrospinal fluid levels of beta-amyloid and tau proteins can be predictive for Alzheimer’s, but this test requires a lumbar puncture, and is inconclusive in many cases.

Magnetic resonance imaging (MRI) of the brain has shown selective atrophy of the hippocampus in patients with early Alzheimer’s (a) vs. normal elderly controls (b), and this technique has been proposed as a diagnostic test for Alzheimer’s, but requires special computerized imaging processing not available at most imaging centers.
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Fluorodeoxyglucose posititon emission tomogrpahy (FDG-PET) shows reduced metabolic activity (uptake of sugar) in the temporal and parietal lobes of patients with early Alzheimer’s (these regions are darker) vs. normal elderly controls (these regions are brighter), and this test is FDA approved, covered by Medicare, and widely available at imaging centers around the counrty:
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A recent study compared the results of MRI, FDG-PET and analysis of CSF biomarkers  in 97 MCI patients, to see which was best for predicting who would convert to Alzheimer’s first. During a mean follow-up of almost 3-years, 43 patients progressed to AD and 54 did not. Of the 3 tests, an abnormal FDG-PET was most predictive.

Before you all rush out and get your FDG-PET to see if you are high risk for Alzheimer’s, be warned that results may be unreliable when the test is performed at an inexperienced center. Data presented at this year’s American Academy of Neurology meeting showed that up to 2/3 of patients referred to a University dementia program had been misdiagnosed with Alzheimer’s dementia based on misread FDG-PET scans performed at community imaging centers.

The Amyvid™ (Florbetapir F 18) PET scan, which was FDA approved this year, actually quantifies the amount of amyloid plaque in affected patients’ brains (bright), and is probably a more promising new PET technique for predicting Alzheimer’s disease. However, this test is not yet covered by Medicare or other insurance covering, and costs between $1500 and $3000:

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In sum, the hope for the future is that with earlier and more accurate diagnosis, future treatments could target Alzheimer’s in its earliest stages, before irreversible brain damage or mental decline has occurred.  However, it is clear that none of the available diagnostic tests are perfect, and although promising, amyloid plaque PET scans are not yet covered by Medicare, so for now we mostly continue to make do with clinical diagnostic criteria.