·
Motor neuron diseases are a group of conditions
that cause the nerves in the spine and brain to lose function over time. They
are a rare but severe form of neurodegenerative disease.Motor neurons are nerve
cells that send electrical output signals to the muscles, affecting the
muscles' ability to function.
·
Motor neuron disease (MND) can appear at any
age, but symptoms usually appear after the age of 40 years.
It affects more men than women.
·
The most common type of MND, amyotrophic lateral sclerosis (ALS),
probably affects up to 30,000 Americans
at any given time, with over 5,600 diagnoses each year, according to the ALS
Association.
·
The
renowned English physicist Stephen Hawking lived with ALS for many decades
until his death in March 2018. Guitar virtuoso Jason Becker is another example
of someone who has been living with ALS for several years.
Types
·
There are several types of
MND. Doctors classify them according to whether they are hereditary or not, and
which neurons they affect.
·
ALS, or Lou Gehrig's disease, is the most common
type, affecting both the upper and lower motor neurons (neurons in the brain
and spinal cord). It affects the muscles of the arms, legs, mouth, and
respiratory system. A person with ALS will live, on average, another 3–5 years, but,
with supportive care, some people live 10 years or more.
·
Primary lateral sclerosis affects the
neurons in the brain. It is a rare form of
MND that advances more slowly than ALS. It is not fatal, but it can affect a
person's quality of life. Juvenile primary lateral sclerosis can affect
children.
·
Progressive bulbar palsy (PBP) involves the
brain stem. People with ALS often have PBP too. The condition causes frequent
choking spells, difficulty speaking, eating, and swallowing.
·
Progressive muscular atrophy (PMA) is a rare
condition that affects the lower motor neurons in the spinal cord. It causes
slow but progressive muscle wasting, especially in the arms, legs, and mouth.
·
Spinal muscular atrophy (SMA) is an
inherited MND that affects children. There are three types, all caused by a
genetic change known as SMA1. It tends to affect the trunk, legs, and arms. The
long-term outlook depends on the type.
·
The different types of MND share similar
symptoms, but they progress at different speeds and vary in severity.
Symptoms
Symptoms
·
MND has three stages — early, middle, and
advanced.
·
Early
stage signs and symptoms
·
In the early stage, symptoms develop slowly and
can resemble those of other conditions. The symptoms will depend on the type of
MND a person has and which part of the body it affects.
- the arms
and legs
- the mouth
- the
respiratory system
·
They include:
- a weakening
grip, which makes it hard to pick up and hold things
- fatigue
- muscle
pains, cramps, and twitches
- slurred
speech
- weakness in
the arms and legs
- clumsiness
and stumbling
- difficulty
swallowing
- trouble
breathing or shortness of breath
- inappropriate
emotional responses, such as laughing or crying
- weight
loss, as muscles lose their mass
· Middle stage signs and symptoms
·
People may also experience:
- muscle
shrinkage
- difficulty
moving
- joint pain
- drooling
due to problems with swallowing
- uncontrollable
yawning, which can lead to jaw pain
- changes in
personality and emotional state
- difficulty
breathing
·
Studies suggest that up to 50% of
people with ALS may experience brain involvement, including memory and language
problems. Around 12–15% of people with ALS may develop dementia.
·
Advanced
stage signs and symptoms
·
Eventually, a person in the advanced stage of
ALS will need help to move, eat, or breathe, and the condition can become
life-threatening.
·
Motor neurons instruct the muscles to move by
sending signals from the brain. They play a role in both conscious and
automatic movements, such as swallowing and breathing.
·
The exact causes are unclear, but the National
Institute of Neurological Diseases and Stroke (NINDS) note that
genetic, toxic, viral, and other environmental factors may play a role.
Risk factors
Risk factors
·
MNDs can occur in adults or children, depending
on the type. They are more likely to affect men than women. Inherited forms of
the condition may be present at birth. They are most likely to appear after the
age of 40 years.
·
The various types may have different risk
factors. SMA is always hereditary, but this is not true for all forms of MND.
·
According to NINDS, around 10% of
ALS cases in the United States are hereditary. It is most likely to appear at
the age of 55–75 years.
·
They also note that veterans appear to have a
1.5–2 times higher chance of developing ALS than non-veterans. This may
indicate that exposure to certain toxins increases the risk of having ALS.
·
A 2012 study found
that footballers have a higher risk of dying from ALS, Alzheimer's disease, and other
neurodegenerative diseases, compared with other people. Experts think that this
could indicate a link with recurrent head trauma.
Diagnosis
·
Doctors often find it difficult to diagnose MND
in the early stages as it can resemble other conditions, such as multiple sclerosis (MS).
·
If a doctor suspects someone has MND, they will
refer them to a neurologist, who will take a medical history, do a thorough
examination, and may suggest other tests, such as:
·
Blood and urine tests: These can help a doctor
rule out other conditions and detect any rise in creatinine kinase, a substance
that muscles produce when they break down.
·
MRI brain scan: An MRI cannot detect an MND, but it can help
rule out other conditions, such as stroke, brain tumor, or unusual brain structures.
·
Electromyography (EMG) and nerve conduction study (NCS):
An EMG tests the amount of electrical activity within muscles, while a NCS
tests the speed at which electricity moves through muscles.
·
Spinal tap, or lumbar puncture: A doctor will
look for changes in the cerebrospinal fluid, which surrounds the brain and
spinal cord. It can help rule out other conditions.
·
Muscle biopsy: This can help detect or rule out a
muscle disease.
·
The doctor will normally monitor the individual
for some time after the tests before confirming that they have MND.
Treatment
·
The correct choice will depend on factors such
as:
- the type of
MND a person has
- the type
and severity of symptoms
- personal
choice
- the
availability and affordability of drugs
·
Slowing
disease progression
·
Drugs appear to be effective at slowing the
progress of some types of MND.
·
For example, the Food and Drug Administration
(FDA) have approved Radicava (Edaravone)
for the treatment of ALS and Spinraza and Zolgensma to
treat SMA.
·
Muscle
cramps and stiffness
·
Medications, such as botulinum toxin (Botox)
injections. Botox blocks the signals from the brain
to the stiff muscles for about 3 months.
·
Baclofen, a muscle relaxer, may help relieve
muscle stiffness, spasms, and yawning. A doctor can surgically implant a small
pump outside the body to deliver regular doses to the space around the spinal
cord, from where it can reach the nervous system.
·
Some people may find physical therapy helps
alleviate cramps and stiffness.
·
Pain
relief
·
A non-steroidal anti-inflammatory drug (NSAID),
such as ibuprofen, will help with mild to moderate pain from muscle cramping as
spasms.
·
A doctor may prescribe stronger pain relief
medication for severe joint and muscle pain in the advanced stages.
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