The 7 most hazardous occupations to the nervous system

A critical part of history taking in medicine is establishing the occupation of the patient. This is because occupational activities and work place exposures are often major contributors to the disease. Furthermore, at the end of the medical process, the eventual diagnosis may have an impact on the patient’s ability to return to work. To be relevant, the occupational history must be exhaustive – it must establish current and past occupations, the tasks carried out, the risk of toxic exposure, and the use of personal protective equipment (PPE). The occupational history is so important to neurology that a whole subspecialty, occupational neuroscience, has emerged to evaluate “the effects of complex environmental and occupational exposure on working people”.

By Ford Madox Brown1QG5Dp3Ti29BxA at Google Cultural Institute, zoom level maximum, Public Domain, Link

So what are the occupational hazards that may lead a patient to the neurologist? Below are my 7 most hazardous occupations to the nervous system

Working together for the commune. Jrwooley6 on Flickr. https://www.flickr.com/photos/jordan_wooley/3861487721

Typing

Previously an occupational hazard restricted to professional typists, carpal tunnel syndrome (CTS) now threatens anyone who uses a computer. CTS develops when the median nerve is entrapped at the wrist, and it manifests as weakness and sensory disturbances over the thumb, the index finger, the middle finger, and half of the ring finger. Whilst desk work is the main risk of CTS, manual workers are not spared the peril because the occupations that increase the risk of CTS include assembly work, food processing and packing, and the use of hand-help powered vibratory tools. And, by the way, vibrating tools also predispose to cubital tunnel syndrome, entrapment of the ulnar nerve at the elbow which presents as weakness and sensory impairment of the little finger, and half of the ring finger (you now know why it was chosen for the wedding ring). Cubital tunnel syndrome, again by the way, also happens to be an occupational hazard of truck drivers, baseball pitchers, and golfers. Just saying.   

Tele typist (ghostwriter). Matthew Hurst on Flickr. https://www.flickr.com/photos/skewgee/4858837387

Farming 

Farming is actually a relatively innocent bystander with this occupational risk, the neurological hazard arising from exposure to pesticides. And the neurological consequence of pesticide use is Parkinson’s disease (PD), a threat that is established without any equivocation. All pesticides carry the same degree of PD risk, but the badge of ignominy surely belongs to organophosphates and carbamates. The risk of PD is however not all-or-none because it is proportional to the duration of exposure. And, as if PD wasn’t enough, pesticides also seem to increase the risk of developing Alzheimer’s disease (AD). I’m just the messenger!

By Manly MacDonaldhttps://www.warmuseum.ca/collections/artifact/1016823, Public Domain, Link

Welding

An almost iconic neurological occupational risk-relationship is the association of welding and Parkinson’s disease (PD). Along with the related tasks of galvanizing and grinding, welding releases fumes of manganese (Mn), the metal that is suspected to be the PD-trigger in this case. As with pesticides, the risk appears to be proportional to the degree of exposure. But unlike pesticides, the reported PD risk of manganese is equivocal because some studies have not found any relationship between welding fumes and PD; indeed one found an inverse relationship between the two, reporting that welding reduces the risk of PD. Surely there are no fumes without fire, but in spite of this minor controversy, or because of it, neurologists are forever vigilant for manganese fumes when they make a diagnosis of PD; they are aware, after all, that only more data will clear the fumes. As an addendum, many other occupations, from teaching to computer programming, reportedly increase the risk of developing PD – presumably because of occupational stress!

By DoriOwn work, CC BY-SA 3.0 us, Link

Smelting

Just as welding conferred notoriety on manganese, so has smelting endowed lead (Pb) with infamy. And the metal’s neurological ignominy is the peripheral neuropathy it evokes. The classical but rarer form of lead neuropathy, is a subacute motor neuropathy which is a manifestation of lead-induced porphyria. Far more common is a chronic sensory neuropathy which is considered to be the direct result of lead toxicity. Beyond neuropathy, chronic lead exposure has garnered disrepute for its reported links with motor neurone disease (MND), although this risk association is contested. In fairness to Pb, other periodic table elements such as thallium (Tl) and arsenic (As) also pose significant occupational risks of neuropathy. And whilst still on metals, it is worth pointing out the report that occupational exposure to iron (Fe) may be a risk factor for meningiomas. Dmitri Mendeleev must be turning in his grave!

By Alfred T. Palmer – This image is available from the United States Library of Congress‘s Prints and Photographs divisionunder the digital ID fsac.1a35280.This tag does not indicate the copyright status of the attached work. A normal copyright tag is still required. See Commons:Licensing for more information., Public Domain, Link

Music

Neurologists, particularly of the movement disorder fraternity, listen to the occupational history of their patients with very keen ears, which literally prick up when they hear that the patient is a musician. This is because a large swathe of musical instruments predispose musicians to career-threatening task-specific dystonia, a form of dystonia which targets muscles that are most frequently exerted, especially in performing delicate actions. Whilst this umbrella diagnosis embraces such non-musical disorders as writer’s cramp, runner’s dystonia, and croupier’s cramp, it is musician’s dystonia that constitutes the widest spectrum of task-specific dystonia. And the reason is not far-fetched: playing musical instruments professionally requires the repetitive performance of very exquisite motor skills over long periods of time. Initially, the dystonia is only evident whilst playing the musical instrument, but it eventually manifests during unrelated tasks, and even at rest. The diversity of symptoms of musician’s dystonia is rivalled only by the number of instruments in the music ensemble, ranging from finger incoordination to upper lip tremor. Singers are also at risk of dysphonia, a form of voice dystonia which they share with teachers, telemarketers and aerobic instructors – all potential victims of hoarseness and voice fatigue.

Musical instrument sculpture in MAMAC in Nice, France. Karen Bryan on Flickr. https://www.flickr.com/photos/europealacarte/17700661556/

Sports

Unsurprisingly, competitive sports takes a heavy toll on the nervous system. At the fairly benign end of the spectrum is the compression of nerves, the innocent victims of grotesquely enlarged, almost mythically Herculean, muscles. Many nerves may be stretched or trapped by a long list of risky sports which includes archery, ballet, baseball, basketball, bowling, football, golf, hockey, tennis, weightlifting, gymnastics, and wrestling. And the classic sport-related nerve entrapment is that of the long thoracic nerve which manifests as scapular winging. Unfortunately, many sporting-related neurological hazards lie at the malign end of the spectrum, with such appalling diseases as chronic traumatic encephalopathy (CTE) from repetitive contact sports; Parkinson’s disease from the boxing related head injuries; and motor neurone disease (MND) especially from professional football. As with most such risks, the evidence for some sports-related neurological hazards is often anecdotal, but very difficult to dismiss in a neurology clinic.

Leicestershire. Ann and David on Flickr. https://www.flickr.com/photos/annedavid2012/42872566454

Shift work

This is, of course, a no brainer as every shift worker knows. Sleep disruption is the most prominent, but by far not the most serious hazard of burning the midnight candle at work. It is common knowledge that shift work reduces alertness, thereby compromising work performance. But more seriously, shift work increases the risk of several neurological disorders such as stroke, epilepsy, Parkinson’s disease (PD), Alzheimer’s disease (AD), and even multiple sclerosis (MS). As if these are not enough, shift work also predisposes to malignancies such as breast cancer and colon cancer, apart from impairing the function of many organs. Indeed the number of disorders now grouped under the remit of shift work sleep disorder (SWSD) is mind-numbing (apologies, I can’t conjure up a better pun). The reason shift work is such a medical nuisance is that it disrupts the brain’s critical circadian rhythm, thereby impairing the production of melatonin, a hormone that plays a hugely critical neuroprotective role. So think twice before taking that next lucrative night shift!

Insomnia. Joana Coccarelli on Flickr. https://www.flickr.com/photos/narghee-la/7294549116

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I suppose the key message of this blog post is…choose your profession wisely!

Why does dystonia fascinate and challenge neurology?

Dystonia is probably the most nebulous of neurological terms. Neurologists use the term for a vast array of neurological diseases. Dystonia also crops up as part of many complex neurological syndromes. Worse still, neurologists also use the name dystonia as a symptom. All quite confusing and perplexing for the lay observer.

Public Domain, Link
Public Domain, Link

No wonder dystonia defies simple definitions. Take the National Institute of Neurological Disorders and Stroke (NINDS) definition which labels dystonia as “a disorder characterized by involuntary muscle contractions that cause slow repetitive movements or abnormal postures“. Then compare it with the NHS Choices definition which sees dystonia as “a medical term for a range of movement disorders that cause muscle spasms and contractions“. We must accept the flexibility of dystonia as both a disorder, and a range of disorders. The defining feature of dystonia however is simple enough-abnormal muscle postures and contractions.

By Katomin at the English language Wikipedia, CC BY-SA 3.0, Link
By Katomin at the English language Wikipedia, CC BY-SA 3.0, Link

The complexity in the definition is just a tip of the iceberg of the things that neurologists find fascinating about dystonia. Here are 5 big reasons why dystonia excites and challenges neurologists.

1. Dystonia is a very visible disorder

Rogers Hartmann at TEDxSMU from tedxsmu on Vimeo.

The abnormal postures that typify dystonia are observable, and the neurologist can describe and define the disorder (or disorders!). This is not the case with many neurological disorders such as migraine, which rely entirely on a history, or epilepsy, which rely heavily on eyewitness accounts. The abnormal postures in dystonia are often very dramatic, and sometimes literally defy description. To help ‘decode’ complex dystonia, neurologists often make video recordings of their patients and send to dystonia experts. And dystonia experts present their own video recordings at neurology conferences, to teach the less initiated of course, but also to flaunt their well-earned expertise.

2. Dystonia is both hereditary and acquired

Von James Heilman, MD - Eigenes Werk, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9445214
Von James Heilman, MDEigenes Werk, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9445214

Many types of dystonia are hereditary. Myoclonus-dystonia and dopa-responsive dystonia (DRD) for example are caused by well-defined genetic mutations. Dystonia is however also frequently acquired, for example as an adverse effect of antidepressant, antipsychotic, and anti-epileptic drugs. Neurologists go to great lengths to sort out what type of dystonia their patients have, bristling with anticipation that the next genetic blood test they send off will clinch the diagnosis. It doesn’t seem to matter that this is often hope trumping experience.

3. Dystonia manifests in a multitude of ways

By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 1194, Public Domain, Link
By Henry Vandyke CarterHenry Gray (1918) Anatomy of the Human Body (See “Book” section below)Bartleby.com: Gray’s Anatomy, Plate 1194, Public Domain, Link

Dystonia may be localised such as with blepharospasm (excessive eyelid twitching), hemifacial spasm, Meige’s syndrome, and cervical dystonia (torticollis). At the same time, dystonia may be generalised as in Wilson’s disease, neuroferritinopathy, and neuroacanthocytosis. Dystonic symptoms often manifest spontaneously, but they may only be task-specific such as in writers cramp and musician’s dystonia. A further way dystonia crops up is as an ally of other movement disorders, as we see with dystonic tremor.

4. Dystonia is a rapidly evolving field

Bootstrap DNA by Charles Jencks, 2003. Mira66 on Flikr. https://www.flickr.com/photos/21804434@N02/3707633630
Bootstrap DNA by Charles Jencks, 2003. Mira66 on Flikr. https://www.flickr.com/photos/21804434@N02/3707633630

Unlike some neurological specialities that are stuck with age-old diseases, dystonia experts regularly describe new dystonia syndromes and genetic mutations, filling up an already crowded taxonomy. An example is the ever-expanding genetic mutations that cause primary dystonia, starting from DYT 1 to DYT 21, and still counting. The field of non-genetic dystonia is also expanding with new disorders such as Watchmaker’s dystonia. Well-established dystonia syndromes also surprise neurologists by manifesting in completely unexpected ways. Recent examples of these new phenotypes are foot drop dystonia resulting from parkin (PARK2) mutation. Neurologists also get excited when they come across known, but rare, presentations of dystonic syndromes such as this recent report on feeding dystonia in chorea-acanthocytosis. 

5. Treatments of dystonia are proliferating

Drugs. Daniel Foster on Flikr. https://www.flickr.com/photos/danielfoster/15097483625
Drugs. Daniel Foster on Flikr. https://www.flickr.com/photos/danielfoster/15097483625

Just as the types of dystonia are burgeoning, so are the treatments. Some interventions are novel, and some have a feel of ‘back to the future’. A few recent examples are treatment of isolated dystonia with zolpidem and selective peripheral denervation for cervical dystonia. Enough to keep the dystonia researchers busy, and to keep their patients feeling valued. Old school treatment such as botulinum toxin however maintain their pride of place. 

Human Genome. Richard Ricciardi on Flikr. https://www.flickr.com/photos/ricricciardi/11622986115
Human Genome. Richard Ricciardi on Flikr. https://www.flickr.com/photos/ricricciardi/11622986115

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For more on dystonia syndromes and treatment, check out:

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Dystonia is a hydra; why not get a concise handle by exploring the dystonia topics in neurochecklists  

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