Alzheimer’s disease (AD) is one of the most fearsome and recalcitrant scourges of neurology. We think we know a lot about it; after all it has been a quite a while since Alois Alzheimer described amyloid plaques and neurofibrillary tangles in his index patient, Frau Deter. But the more neuroscientists study the disease, the murkier the field looks. For example, we are still not quite sure what the plaques and tangles really signify; for all we know, they may just be innocent bystanders, powerless by-products of a neurodegenerative process that defies understanding. We have accumulated an endlessly long list of AD risk factors, but we have singularly been unable to point a finger at the cause of AD.
This elusive void may however be a void no longer, if what superficially appears to be an outlandish theory turns out to be correct. And the theory is that AD is caused by infection! Just take a deep breathe, and allow yourself the space to make a giant leap of imagination. My attention was first drawn to the infective hypothesis of AD by a headline in Scientific American screaming Controversial New Push to Tie Microbes to Alzheimer’s Disease. The obvious key word here of course is controversial: is it possible that AD, this quintessential neurodegenerative disease, is…just another chronic infection?
To find the original source of the story, the trail of bread crumbs led to an editorial published in the Journal of Alzheimer’s Disease in 2016, plainly titled Microbes and Alzheimer’s Disease. But this is not a run-of-the-mill editorial at all because it was written by 33 senior scientists and clinicians from a dozen countries. And their reason for an alternative theory of AD is simple: amyloid, the long-suspected culprit for decades, has failed to live up to its billing. They point out that amyloid exists harmlessly in the brains of many older people who never go on to develop dementia. They also cite studies which demonstrate that treating amyloid, by immunological means, does not improve the state of people suffering from AD. Amyloid, in other words, is not such a bad guy after all. But all the while we have been setting traps to ensnare it, the microbial villains have been running amok, having a field day.
But why should microbes succeed where amyloid, the ubiquitous protein, has woefully failed? The editorial gave 8 good reasons to argue that the infection theory is better than the amyloid hypothesis. One reason is that the brains of people with AD are often riddled with inflammation, a characteristic feature of infections. Another reason is the observation that AD can be transferred to primates when they are inoculated with the brain tissue of someone with AD.
And the culprit with the most number of index fingers pointing at it is herpes simplex virus type 1 (HSV1). The editorial tells us that there have been about 100 publications, by different groups, demonstrating that HSV1 is a ‘major factor‘ in the causation of AD. Some of these studies have shown that people with AD have immunological signs of significant HSV infection in their blood. The editorial goes further to review the possible mechanisms by which HSV1 may cause AD; one of these is the possibility that the virus lowers the risk of AD in people who possess the APOE ɛ4 allele genetic liability.
Just when you are getting your head round the idea, the infection theory takes a very sinister turn. And this relates to the perversemodus operandi of the microbes. The authors tell us that the microbes first gain access to the brains of their victims when they (the victims) were much younger. Like sleeper cells in their ghoulish crypts, the microbes hibernate, biding their time until their victims get older, and their immunity declines. The microbes then awaken, and like malevolent zombies, set out to wreak gory mayhem and cataclysmic destruction. And they do this either by causing direct damage to the brain, or indirectly by inducing inflammation.
You can now descend form your giant imaginative leap and start to wonder: if AD is indeed caused by microbes, what can we do about it? ‘Tis time for some down-to-earth deep thinking.
Traumatic brain injury (TBI) is simply disheartening. It is particularly devastating because it usually affects young people in their prime, with the consequent personal, social, and economic consequences. This blog has previously touched a little on TBI with the post titled Will Smith and chronic traumatic encephalopathy?This was a light-hearted take on concussion in sports, but traumatic brain injury is nothing but a serious burden. So what are the big brains in white coats doing to take down this colossus? Quite a lot it seems. Here, for a taster, are 9 promising advances in the management of traumatic brain injury.
Better understanding of pathology
An amyloid PET imaging study by Gregory Scott and colleagues, published in the journal Neurology, reported a rather surprising link between the pathology seen in long-term survivors of traumatic brain injury, with the pathology seen in Alzheimers disease (AD). In both conditions, there is an increased burden of β-amyloid (Aβ) in the brain, produced by damage to the nerve axons. The paper, titled Amyloid pathology and axonal injury after brain trauma, however notes that the pattern of Aβ deposition in TBI can be distinguished from the one seen in AD. The big question this finding raises is, does TBI eventually result in AD? The answer remains unclear, and this is discussed in the accompanying editorial titled Amyloid plaques in TBI.
Blood tests to detect concussion
The ideal biomarker for any disorder is one which is easy to detect, such as a simple blood test. A headline that screams Blood test may offer new way to detect concussionsis therefore bound to attract attention. The benefits of such a test would be legion, especially if the test can reduce the requirement for CT scans which carry the risks of radiation exposure. This is where glial fibrillary acidic protein (GFAP) may be promising. The research is published in the journal, Academic Research Medicine, with a rather convoluted title, Performance of Glial Fibrillary Acidic Protein in Detecting Traumatic Intracranial Lesions on Computed Tomography in Children and Youth With Mild Head Trauma. The premise of the paper is the fact that GFAP is released into the blood stream from the glial cells of the brain soon after brain injury. What the authors therefore did was to take blood samples within 6 hours of TBI in children. And they demonstrated that GFAP levels are significantly higher following head injury, compared to injuries elsewhere in the body. This sounds exciting, but we have to wait and see where it takes us.
Brain Scars Detected in Concussionsis the attention-grabbing headline for this one, published in MIT Technology Review. Follow the trail and it leads to the actual scientific paper in the journal Radiology, with a fairly straight-forward title, Findings from Structural MR Imaging in Military Traumatic Brain InjuryThe authors studied >800 subjects in what is the largest trial of traumatic brain injury in the military. Using high resolution 3T brain magnetic resonance imaging (MRI), they demonstrated that even what is reported as mild brain injury leaves its marks on the brain, usually in the form of white matter hyperintense lesions and pituitary abnormalities. It simply goes to show that nothing is mild when it comes to the brain, the most complex entity in the universe.
Implanted monitoring sensors
Current technologies which monitor patients with traumatic brain injury are, to say the least, cumbersome and very invasive. Imagine if all the tubes and wires could be replaced with microsensors, smaller than grains of rice, implanted in the brain. These would enable close monitoring of critical indices such as temperature and intracranialpressure. And imagine that these tiny sensors just dissolve away when they have done their job, leaving no damage. Now imagine that all this is reality. I came across this one from a CBS News piece titled Tiny implanted sensors monitor brain injuries, then dissolve away. Don’t scoff yet, it is grounded in a scientific paper published in the prestigious journal, Nature, under the title Bioresorbable silicon electronic sensors for the brain. But don’t get too exited yet, this is currently only being trialled in mice.
Drugs to reduce brain inflammation
What if the inflammation that is set off following traumatic brain injury could be stopped in its tracks? Then a lot of the damage from brain injury could be avoided. Is there a drug that could do this? Well, it seems there is, and it is the humble blood pressure drug Telmisartan. This one came to my attention in Medical News Today, in a piece titled Hypertension drug reduces inflammation from traumatic brain injury. Telmisartan seemingly blocks the production of a pro-inflammatory protein in the liver. By doing this, Telmisartan may effectively mitigate brain damage, but only if it is administered very early after traumatic brain injury. The original paper is published in the prestigious journal, Brain, and it is titled Neurorestoration after traumatic brain injury through angiotensin II receptor blockage. Again, don’t get too warm and fuzzy about this yet; so far, only mice have seen the benefits.
Treatment of fatigue
Fatigue is a major long-term consequence of traumatic brain injury, impairing the quality of life of affected subjects in a very frustrating way. It therefore goes without saying, (even if it actually has to be said), that any intervention that alleviates the lethargy of TBI will be energising news. And an intervention seems to be looming in the horizon! Researchers writing in the journal, Acta Neurologica Scandinavica, have reported that Methylphenidate significantly improved fatigue in the 20 subjects they studied. Published under the title Long-term treatment with methylphenidate for fatigue after traumatic brain injury, the study is rather small, not enough to make us start dancing the jig yet. The authors have rightly called for larger randomized trials to corroborate their findings, and we are all waiting with bated breaths.
Treatment of behavioural abnormalities
Many survivors of traumatic brain injury are left with behavioural disturbances which are baffling to the victim, and challenging to their families. Unfortunately, many of the drugs used to treat these behaviours are not effective. This is where some brilliant minds come in, with the idea of stimulating blood stem cell production to enhance behavioural recovery. I am not clear what inspired this idea, but the idea has inspired the paper titled Granulocyte colony-stimulating factor promotes behavioral recovery in a mouse model of traumatic brain injury. The authors report that the administration of G‐CSF for 3 days after mild TBI improved the performance of mice in a water maze…within 2 weeks. As the water maze is a test of learning and memory, and not of behaviour, I can only imagine the authors thought-surely only well-behaved mice will bother to take the test. It is however fascinating that G‐CSF treatment actually seems to fix brain damage in TBI, and it does so by stimulating astrocytosis and microgliosis, increasing the expression of neurotrophic factors, and generating new neurons in the hippocampus“. The promise, if translated to humans, should therefore go way beyond water mazes, but we have to wait and see.
Drugs to accelerate recovery
The idea behind using Etanercept to promote recovery from brain injury sound logical. A paper published in the journal, Clinical Drug Investigation, explains that brain injury sets off a chronic lingering inflammation which is driven by tumour necrosis factor (TNF). A TNF inhibitor will therefore be aptly placed to stop the inflammation. What better TNF inhibitor than Eternacept to try out, and what better way to deliver it than directly into the nervous system. And this is what the authors of the paper, titled Immediate neurological recovery following perispinal etanercept years after brain injury, did. And based on their findings, they made some very powerful claims: “a single dose of perispinal etanercept produced an immediate, profound, and sustained improvement in expressive aphasia, speech apraxia, and left hemiparesis in a patient with chronic, intractable, debilitating neurological dysfunction present for more than 3 years after acute brain injury”. A single patient, mind you. Not that I am sceptical by nature, but a larger study confirming this will be very reassuring.
And finally, that elusive holy grail of neurological therapeutics, neuroprotection. Well, does it exist? A review of the subject published in the journal, International Journal of Molecular Sciences, paints a rather gloomy picture of the current state of play. Titled Neuroprotective Strategies After Traumatic Brain Injury, it said “despite strong experimental data, more than 30 clinical trials of neuroprotection in TBI patients have failed“. But all is not lost. The authors promise that “recent changes in experimental approach and advances in clinical trial methodology have raised the potential for successful clinical translation”. Another review article, this time in the journal Critical Care, doesn’t offer any more cheery news about the current state of affairs when it says that the “use of these potential interventions in human randomized controlled studies has generally given disappointing results”. But the review, titled Neuroprotection in acute brain injury: an up-to-date review, goes through promising new strategies for neuroprotection following brain injury: these include hyperbaric oxygen, sex hormones, volatile anaesthetic agents, and mesenchymal stromal cells. The authors conclude on a positive note: “despite all the disappointments, there are many new therapeutic possibilities still to be explored and tested”.
What an optimistic way to end! We are not quite there yet, but these are encouraging steps.
The Neurology Lounge strives hard to keep to the straight and narrow path of clinical neurology. But every now and then it takes a peek at what is happening at the cutting edge of neuroscience. And what can be more cutting edge then biomarkers, with their promise of simplifying disease identification, making prompt and accurate diagnosis an effortless task.
The quintessential biomarker however remains as elusive as quicksilver. Not that one could tell, going by the rate biomarkers are being spun from the neuroscience mills. Biomarkers are the buzz in many neurological fields, from brain tumours to multiple sclerosis (MS), from Alzheimer’s disease (AD) to Huntington’s disease (HD).
The proliferation of contending biomarkers is however probably highest in the field of motor neurone disease (MND). Is there a holy grail out there to enable the rapid and accurate diagnosis of this relentlessly progressive disease? There is clearly no dearth of substances jostling for prime position in the promised land of MND biomarkers. Below is a shortlist of potential MND CSF biomarkers; just click on any to go to the source!
Biomarkers elevated in the cerebrospinal fluid (CSF)
Neurology embodies some of the most dreadful diseases known to man. Every neurological disorder is disheartening, each characterised by unique frustrations for patients and their families. It is difficult to quantify the distress and misery these afflictions impose on their victims, and even harder to appreciate the despair and anguish they evoke in those who care for them.
It is clearly hard to compare the impact of different neurological diseases. Some neurological disorders however stand out because of the consternation their names evoke, and the terror that follows in their wake. These diseases come with unimaginable physical and psychological burdens, and crushing demands on human and material resources. They impose either a debilitating morbidity, or a hasty mortality.
The nervous system ailments in the list below pose exacting therapeutic challenges, resistant as they are to all attempts at treatment or cure. This list sets out to emphasise the urgency for neuroscience to find a remedy for each of them, but it does not intend to belittle the horror of the disorders omitted from it. The choice of the number 13 is, sadly, self-evident. Here then are the top 13 most dreadful neurological disorders…all with gold links to the associations helping to defeat them.
Ataxia, in lay terms, is incoordination. This typically manifests as an unsteady gait and clumsiness. Ataxia converts all activities of daily living into burdensome chores. Whilst many types of ataxia are preventable or reversible, primary ataxias are progressive and carry a dismal outlook. In this category are Spinocerebellar ataxia (SCA), Friedreich’s ataxia, and Ataxia telangiectasia. You may read more about ataxia in these previous blog posts:
Brain cancers hardly need any description. They are either primary, arising from the brain cells, or metastatic, spreading to the brain from other organs. Some primary brain cancers, such as meningiomas and pituitary tumours, are, relatively, treatable. Many others are unfortunately ominously malignant. The most dreadful in this category is surely the spine-chilling glioblastoma multiforme. You may check out these previous blog posts for more on these tumuors:
Peripheralneuropathy is ubiquitous in the neurology clinic. Neuropathy may result from reversible situations such as overindulgence in alcohol, uncontrolled diabetes, or Vitamin B12 deficiency. Neuropathy is often just a minor inconvenience when it manifests with sensory symptoms such as tingling and numbness. It may however be debilitating when it presents as limb paralysis, or complicated by major skeletal deformities. At the severe end of the spectrum of neuropathy are the hereditary forms such as CharcotMarie Tooth disease (CMT) and Familialamyloid polyneuropathy. Read more in these blog posts:
CJD is the most iconic of the prion diseases. These disorders are as horrendous as they are enigmatic, defying categorisation as either infections or neurodegenerative diseases. More puzzling is their ability to be either hereditary and acquired. CJD exists in the classic or variant form, but both share a relentlessly rapid course, and a uniformly fatal end. You may read more in these previous blog posts titled:
Dystonia marks its presence by distressing movements and painful postures. At its most benign, dystonia is only a twitch of the eyelid (blepharospasm) or a flicker of one side of the face (hemifacial spasm). At the extreme end, it produces continuous twisting and swirling motions, often defying all treatments. The causes of dystonia are legion, but the primary dystonias stand out by their hereditary transmission and marked severity. Read more on dystonia in these blog posts:
Huntington’sdisease is an iconic eponymous neurological disorder which is marked by the vicious triumvirate of chorea, dementia, and a positive family history. It is an awful condition, often driving its victims to suicide. It is a so-called trinucleotide repeat expansion disorder, implying that successive generations manifest the disease at an earlier age, and in more severe forms (genetic anticipation). You may read more on HD in the previous blog post titled:
Also known as Amyotrophiclateral sclerosis (ALS), MND is simply devastating. Recognising no anatomical boundaries, it ravages the central and peripheral nervous systems equally. MND creeps up on the neurones and causes early muscle twitching (fasciculations) and cramps. It then gradually devours the nerves resulting in muscle wasting, loss of speech, ineffectual breathing, and impaired swallowing. Our previous blog posts on MND are:
Multiple sclerosis is a very common disease, and gets more common the further away you get from the equator. It is the subject of intense research because of the devastation it foists on predominantly young people. Many drugs now ameliorate, and even seem to halt the progression of, relapsing remitting MS (RRMS). This is however not the case with primary progressive MS (PPMS) which, until the introduction of ocrelizumab, defied all treatments. There are many contenders vying for the cause of MS, but the reason nerves in the central nervous system inexplicably lose their myelin sheaths remains elusive. You may read more on MS in these blog posts:
Rabies, a rhabdovirus, is a zoonosis-it is transmitted to man by a wide range of animals such as dogs, bats, racoons, and skunks. It is the quintessential deadly neurological disease, popularised by the Steven King book and film, Cujo. Rabies manifests either as the encephalitic (furious) or the paralytic (dumb) forms. It wreaks havoc by causing irritability, hydrophobia (fear of water), excessive sweating, altered consciousness, and inevitably death. Whilst there are vaccines to protect against rabies, a cure has eluded neuroscientists. This blog is yet to do justice to rabies but it is, at least, listed in the post titled What are the most iconic neurologicaldisorders? But you could better by checking neurochecklists for details of the clinicalfeatures and management of rabies.
Nothing is quite as heart-wrenching as the sudden loss of body function that results from spinal cord trauma. This often causes paralysis of both legs (paraplegia), or all four limbs (quadriplegia). This life-changing disorder is often accompanied by loss of control over bowel and bladder functions, and complications such as bed sores and painful spasms. You may read about the heroic efforts to treat spinal cord injury in the blog posts titled:
Tetanus is an eminently preventable disease, now almost wiped out in developed countries by simple immunisation. It however continues its pillage and plunder in the developing world. It strikes young and old alike, often invading the body through innocuous wounds. Tetanus is caused by tetanospasmin and tetanolysin, the deadly toxins of the bacterium Clostridium tetani. The disease is classified as generalised, localised, cephalic, or neonatal tetanus. It is characterised by painful spasms which manifest as lockjaw (trismus), facial contortions (risus sardonicus), trunkal rigidity (opisthotonus), and vocal cord spasms (laryngospasm). The disease is awfully distressing and, when advanced, untreatable. It is a stain on the world that this avoidable disorder continuous to threaten a large number of its inhabitants. Check neurochecklists for more on the pathology,clinicalfeatures, and management of tetanus.
As for all lists, this will surely be subject to debate, or perhaps some healthy controversy. Please leave a comment.
In the excellent book, The Innovators Prescription, the authors predict that precisionmedicinewill replace intuitive medicine, and diseases will be defined by their underlying metabolic mechanisms, and not by the organs they affect, or the symptoms they produce. Clayton Christensen and colleagues argue that this precise definition of diseases will lead to more effective treatments. But they also show that precision medicine will show that many different diseases actually share the same underlying metabolic derangements. Many disparate diseases will therefore turn out to be just mere manifestations of the same metabolic disease.
Why should Liraglutide work so well in both diabetes and Alzheimer’s, diseases with apparently different pathologies? The answer lies in insulin resistance, the underlying mechanism of type 2 of diabetes; there is now evidence that insulin resistance contributes to dementia. If this is the case, Liraglutide, by improving glucose metabolism, could potentially treat both diabetes and Alzheimer’s disease.
To explore this potential further, there is now a large multicentre trial exploring the real benefit of Liraglutide in Alzheimer’s disease. Titled Evaluating Liraglutide in Alzheimer’s Disease or ELAD, it is recruiting people with mild disease, aged between 50-85 years old, and who do not have diabetes. As they say, watch this space!
But why is a neurologist talking about seahorses. It’s all in the name. The Latin name for seahorse is hippocampus , derived from hippos for horse, and kampos for sea monster. Where biologists saw fish, the ancients saw monsters. And you really can’t blame them…take a closer look
It is no mystery why neuroanatomists name this important part of the brain after the seahorse, the resemblance is eerily striking.
Neurologists are passionate about the hippocampus for various reasons. In people with memory complaints, for example, hippocampal atrophy may predict the development of Alzheimer’s disease . A shrunken hippocampus is also seen in some forms of epilepsy. Neurologists thereforeendlessly harangue their neuroradiology colleagues to look closely at their patients’ brain MRI scans, and to tell them that the hippocampus is shrunken…even if it’s just a little bit smaller. Unfortunately for the neuroradiologists, the MRI scans do not come colour-coded as in the illustrative scan below.
This blog post is however about major depression, and not about epilepsy or dementia. Depression, that bad feeling we all feel every now and then is frustrating, but major depression is devastating. And we now know that it is accompanied by major alterations in the structure of the brain. And, yes, the changes are in the hippocampus. I got interested in this subject when I came across a piece in Neurology News reporting that people with depression have a smaller hippocampus.
The association of depression with hippocampal atrophy is however an old one. Proceedings of the National Academy of Science (PNAS) reviewed the relationship in an editorial from 2011 titledDepression, antidepressants, and the shrinking hippocampus. The author addressed the unresolved puzzle…which of the two came first. Reminiscent of the chicken and egg scenario, it is not clear if the hippocampal atrophy causes depression, or vice versa. To add to the puzzle, the paper conjectured the possibility of a third, unknown agent, causing both the depression and the small hippocampus.
This question was the focus of a meta-analysis published in Molecular Psychiatry this year. It reviewed the brain imaging data of 15 studies, involving about 1700 people with major depression. Titled Subcortical brain alterations in major depressive disorder, the authors confirmed the link between depression and hippocampal atrophy, and also showed that the shrinkage is worse in those who developed depression at an early age, and in those who have had frequent episodes of depression.
Does depression lead to hippocampal atrophy? The meta-analyses hinted so, but there were too many caveats for the authors to arrive at a definitive conclusion. They admit that more needs to be done to unravel depression….leaving the mystery of the shrinking seahorses to continue to another day.
Neurology is a broad specialty covering a staggering variety of diseases. Some neurological disorders are vanishingly rare, but many are household names, or at least vaguely familiar to most people. These are the diseases which define neurology. Here, in alphabetical order, is my list of the top 60 iconic neurological diseases, with links to previous blog posts where available.
The Neurology Lounge has a way to go to address all these diseases, but they are all fully covered in neurochecklists. In a future post, I will look at the rare end of the neurological spectrum and list the 75 strangest and most exotic neurological disorders.