Multiple Sclerosis (MS) and Amyotrophic Lateral Sclerosis (ALS) – the latter of which is also known as Lou Gehrig's disease – are both neurodegenerative diseases. They share a handful of similarities, including some symptoms, but under the surface, they are very different conditions.
What is Multiple Sclerosis?
Multiple sclerosis (MS) is an autoimmune disease that attacks the fatty substance, called myelin, that forms protective covers around fibers (axons) of the central nervous system (CNS). This demyelination can lead to a range of symptoms relating to the CNS.
Because the CNS coordinates and influences both voluntary and involuntary activity all over the body, MS is extremely unpredictable, and the disease varies from person to person. Some of the most common symptoms include impaired cognitive abilities (memory, concentration, reasoning, problem-solving, etc.), fatigue, muscle weakness, spasms, numbness, tingling, and vision problems.
The ‘type’ of MS one lives with is defined by the way in which symptoms occur; some people experience distinct relapses (relapsing-remitting MS), others have a more progressive worsening of the disease (primary- and secondary-progressive MS). It is often argued that the types of MS are not truly independent of one another; rather, there is something of a spectrum upon which individuals fall. You can read more about the different types of MS here:
What is ALS?
Amyotrophic lateral sclerosis (ALS) is perhaps better known as Lou Gehrig’s disease in North America, named after the legendary baseball player who died of the disease in 1941.
ALS is a type of motor neuron disease (MND). Motor neurons, which are cells that control voluntary and involuntary muscle movements, are killed, preventing signals from reaching muscles and thus causing them to deteriorate (a process known as atrophy).
Upper motor neurons are in the brain, while lower motor neurons are in the spinal cord. “Classic” ALS is characterized by both upper and lower neurons deteriorating, and accounts for two-thirds of cases.
Other forms, with definitions from John Hopkins Medicine, are:
Primary Lateral Sclerosis (PLS) - a progressive neurological disease in which the upper motor neurons (nerve cells) deteriorate. If the lower motor neurons are not affected within two years, the disease usually remains a pure upper motor neuron disease. This is the rarest form of ALS.
Progressive Bulbar Palsy (PBP) - a condition that starts with difficulties in speaking, chewing and swallowing due to lower motor neuron (nerve cell) deterioration. This disorder affects about 25% of those with ALS.
Progressive Muscular Atrophy (PMA) - a progressive neurological disease in which the lower motor neurons (nerve cells) deteriorate. If the upper motor neurons are unaffected within two years, the disease usually remains a pure lower motor neuron disease.
Some people consider PLS, PBP, and PMA to be separate conditions from classic ALS, all of which can be classed as motor neuron diseases. Others consider them to be sub-types of ALS (in which case ALS and MND may be used interchangeably).
Symptoms can start in different parts of the body, depending on which motor neurons are damaged first. ALS progression usually follows a predictable pattern – the initial symptoms continue to worsen, and other body parts are eventually affected. In the latter stages, it leads to complete paralysis and respiratory failure.
ALS does not affect one’s senses, nor one’s intellectual reasoning.
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Differences Between MS & ALS
Role of the Immune System
Multiple sclerosis is an autoimmune disease, meaning the immune system mistakenly attacks healthy cells within the body. The immune system seems to react to healthy cells as though they were antigens (foreign invaders from viruses, infections, etc.), creating autoantibodies to attack them.
In the case of MS, the myelin sheath is the target of the autoantibodies. In other autoimmune diseases, autoantibodies attack different cells (in the case of rheumatoid arthritis, for example, it is the tissue of the joints).
Unlike MS, amyotrophic lateral sclerosis is not considered an autoimmune disease.
There is evidence that neuroinflammation plays a role in its pathogenesis. Along with the activation of immune system cells in the brain (such as microglia and T-cells), this does suggest the immune system does play a role in the mechanisms and progression of ALS.
However, the precise nature of the immune system’s involvement is not well understood. At least one recent study even suggests that microglia actually protect motor neurons rather than contribute to their death.
The exact nature of ALS is not yet known, but there is no conclusive evidence to suggest the underlying mechanisms are similar to those of MS.
Risk Factors & Incidence
As is common when it comes to autoimmune diseases, women are around three times likelier to develop multiple sclerosis than men are. It is usually diagnosed between 20 and 50 years of age.
Amyotrophic lateral sclerosis, on the other hand, is more common in men and usually occurs later in life than MS, with an average age of onset of around 55 to 60 years old.
Mysteriously, military veterans are twice as likely to develop ALS than the general population. It’s not known why this is the case, although greater exposure to toxins, such as lead, is one theory. No such link exists with MS.
MS is more common than ALS. The incidence rate in the USA is between 57 and 78 cases per 100,000 people in the southern states, and between 110 and 140 per 100,000 in the northern states. This geographical discrepancy is not limited to the USA; around the globe, MS tends to be more prevalent in places farther from the equator.
This has led to the theory that a lack of vitamin D, the production of which is prompted by UVB radiation from sunlight, may contribute to the development of MS.
While incidence rates of ALS vary around the globe, no such geographical pattern has been identified, suggesting the environmental risk factors differ for the two conditions.
In the USA, there are roughly 5,000 diagnoses per year, with an incidence rate of around 2 in every 100,000 people. It is estimated that around 16,000 people in the USA live with the ALS at any given time.
While some of the early symptoms of multiple sclerosis and amyotrophic lateral sclerosis may be similar, most are markedly different.
Symptoms of MS that are not common to those with ALS include:
- Numbness and tingling
- Vision problems
- Cognitive changes
- Hearing loss
- Bowel and bladder problems
- Heat sensitivity
ALS, on the other hand, does not affect the nerves that control the senses, nor does it usually cause bladder problems. Rather than having the mental impact MS does, ALS is a purely physical degenerative disease.
As the disease progresses, symptoms of ALS that are not common to MS include:
- Difficulty breathing
- Difficulty swallowing
Multiple sclerosis is completely unpredictable. Upon diagnosis, it is impossible to tell how the disease will progress or which symptoms are likely to occur.
Many people with relapsing-remitting MS, for example, will develop secondary-progressive MS – whereby relapses cease and, instead, symptoms gradually worsen – but how long this transition takes, if it happens at all, is unpredictable.
Likewise, while it is estimated that two-thirds of people with MS remain able to walk, there is no way to predict the long-term effect on mobility on a case-by-case basis.
MS is not usually fatal. Improved treatments have helped increase the life expectancy of people with MS, which is now estimated to be five to 10 years lower than the general population.
Amyotrophic lateral sclerosis is usually much more predictable. In the majority of cases, ALS is a rapidly progressing and fatal disease. Until treatment that can effectively slow, stop, or even reverse the progression of the disease is developed, most people live for around three to five years after their diagnosis.
Around 10% of people with ALS live for 10 years or longer after their diagnosis. Physicist, Stephen Hawking, lived with ALS for 55 years prior to his death in 2018, perhaps the longest anyone has ever lived with the condition.
Similarities Between MS & ALS
The most obvious similarity between multiple sclerosis and amyotrophic lateral sclerosis is the shared use of the word ‘sclerosis’. Sclerosis, in medical terms, means hardening or stiffening of a structure.
When it comes to MS, sclerosis refers to the scars (or plaques/legions) that are caused by the damage done to the myelin sheath.
In ALS, lateral sclerosis refers to the stiffening of the lateral columns in the spine, which is a consequence of muscle being worn away.
Some of the early symptoms of ALS are similar to common MS symptoms, including:
- Twitching & spasms
- Trouble walking
- Muscle pain
- Muscle weakness and/or stiffness
As mentioned earlier, however, the symptoms become more diverse as each disease progresses.
Complex Genetic Disorders
Like nearly all (if not all) chronic diseases, genetics almost certainly play a key role in the development of MS and ALS. While some diseases, such as cystic fibrosis, are caused by a mutation to a single gene, both MS and ALS are polygenic. This means many genes have been associated with each condition.
Hundreds of genes have been identified as being more prevalent in people with MS than the general population.
It seems that the more of these genes you possess, the greater your risk of developing MS. As well as genetics, environmental and lifestyle factors – such as vitamin D deficiency and smoking – have been associated with an increased risk.
It is suspected that while the above factors may determine your risk, something else actually triggers the development of the disease. When it comes to MS, viruses (particularly human herpesviruses, such as Epstein-Barr virus) may well be the trigger, although the nature of the relationship is not fully understood.
Genetics, therefore, is just one component in an extremely complex process that leads to MS, making it impossible to predict whether you will actually develop either disease based on your genetic profile.
You can read more about the role of genetics in the development of MS here:
Genetics also play a role in the development of ALS; 5% to 10% of cases are inherited (or familial). For the remaining cases, however, the cause is unknown.
Even in non-familial ALS, at least 25 different genes have thus far been associated with ALS. As is the case with MS, it is suspected that with each additional gene one carries, the slightly greater the risk of ALS becomes.
Other observations include the presence of a protein called ubiquilin 2, which may play a role, and high levels of a chemical called glutamate. There is evidence that glutamate may be one of the driving forces in the destruction of motor neurons.
However, quite how all of these elements combine to cause ALS remains unknown. Like MS, it is extremely complex puzzle, the genetic pieces to which complete only part of the picture.
Perhaps more important than anything else written here, no cure yet exists for either MS or ALS.
Disease-modifying drugs for MS can help slow the progression of the disease, although such drugs are not suitable for everyone, are not guaranteed to work, and can have severe side effects. Other treatments tend to focus on recovery from relapses and treating specific symptoms.
Two disease-modifying drugs to slow the progression of ALS have been approved in the USA. However, their effect is often modest at best and in many cases, treatment focuses on limiting the severity of symptoms and maintaining the best quality of life possible for as long as possible.
Ultimately, each disease can have a devastating impact on those diagnosed and their loved ones.
As researchers uncover more information about MS and ALS, it can be hoped that more effective treatment options – and one day a cure – will be another similarity to add to the list.
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