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Neuromuscular Disorders
Amyotrophic Lateral Sclerosis
• Amyotrophic Lateral Sclerosis (ALS) or Lou
Gehrig Disease
– Neuromuscular disorder characterized by
progressive degeneration of upper and lower
motor neurons leading to loss of skeletal muscle
strength, including the respiratory muscles
–
http://www.youtube.com/watch?v=3cmk4cbgTCU
Amyotrophic Lateral Sclerosis
• Etiology
– Heredity – 8 to 10% of cases are familial
– More common in males than females (2:1)
– Most common in ages 40 – 60
– 1 - 2 persons/100,000 in the U.S.
– Prognosis is poor
Amyotrophic Lateral Sclerosis
• Etiology
– Exact etiology unknown
• Genetic mutation present in 10 – 15% of patients
increases the susceptibility of neurons to oxidative
stress
• Possible links to pesticides and other neurotoxic
chemicals
Amyotrophic Lateral Sclerosis
• Etiology
• Susceptibility to glutamate-induced neurotoxicity –
glutamate is the principal excitatory brain
neurotransmitter; decrease in uptake of glutamate may
lead to overstimulation of glutamate receptors leading
to increased intracellular calcium, triggering production
of a proteolytic enzymes causing cell membrane injury
Amyotrophic Lateral Sclerosis
• Pathophysiology
– Progressive death of both upper and lower motor neurons in
the motor cortex of the brain, the brain stem, and the spinal
cord
– Begins usually with weakness of large muscle groups or the
bulbar muscles (those supplied by nerves in the upper spinal
cord, such as those controlling swallowing and speaking)
Amyotrophic Lateral Sclerosis
• Pulmonary Function Findings
– Progressive decrease in FVC
– Decreased MVV
– Increase in RV
– Decrease in NIF
Amyotrophic Lateral Sclerosis
• Pulmonary Function Findings
– Will require ventilatory assistance when criteria
are met
• PaCO2 > 45 mmHg
• VC < 20 ml/kg
• NIF < -20mmHg
• VT < 5 ml/kg
Amyotrophic Lateral Sclerosis
• Clinical Findings
– Progressive weakness of distal extremities
– If early involvement of phrenic nerve, then nocturnal
hypoventilation followed by acute respiratory failure
– Progressive deterioration of pulmonary function
results
– Difficulty in swallowing
– Difficulty in speech
– Prognosis is poor with 80% mortality within five years
of diagnosis
ALS diagnosis
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No test can provide a definite diagnosis of ALS, although the presence of upper
and lower motor neuron signs in a single limb is strongly suggestive. Instead, the
diagnosis of ALS is primarily based on the symptoms and signs the physician
observes in the patient and a series of tests to rule out other diseases. Physicians
obtain the patient's full medical history and usually conduct a neurologic
examination at regular intervals to assess whether symptoms such as muscle
weakness, atrophy of muscles, hyperreflexia, and spasticity are getting
progressively worse.
MRI demonstrates increased T2 signal within the posterior part of the internal
capsule, consistent with the clinical diagnosis of ALS.
Because symptoms of ALS can be similar to those of a wide variety of other, more
treatable diseases or disorders, appropriate tests must be conducted to exclude
the possibility of other conditions. One of these tests is electromyography (EMG),
a special recording technique that detects electrical activity in muscles
ALS treatment
• Slowing progression of disease, no cure exist
• RT treatment: bronchial hygiene, trachestomy,
continuous mechanical ventilation
Neuromuscular Disorders - GuillainBarre Syndrome
• is an acute polyneuropathy, a disorder affecting
the peripheral nervous system. Ascending
paralysis, weakness beginning in the feet and
hands and migrating towards the trunk, is the
most typical symptom, and some subtypes cause
change in sensation or pain as well as dysfunction
of the autonomic nervous system. It can cause
life-threatening complications, in particular if the
breathing muscles are affected or if there is
autonomic nervous system involvement. The
disease is usually triggered by an infection.
Plasmaphoresis
• Plasmapheresis is the removal, treatment,
and return of (components of) blood plasma
from blood circulation. It is thus an
extracorporeal therapy (a medical procedure
which is performed outside the body). The
method is also used to collect plasma, to
preserve it frozen and to keep it fresh. Finally,
the frozen plasma is manufactured into a
variety of medications.
GB
• Polyneuropathy is a neurological disorder that occurs
when many nerves throughout the body malfunction
simultaneously.
• The diagnosis is usually made by nerve conduction
studies and with studies of the cerebrospinal fluid.
With prompt treatment by intravenous
immunoglobulins or plasmapheresis, together with
supportive care, the majority will recover completely.
Guillain–Barré syndrome is rare, at 1–2 cases per
100,000 people annually, but is the most common
cause of acute non-trauma-related paralysis in the
world.
Neuromuscular Disorders - GuillainBarre Syndrome
• Most common peripheral neuropathy causing respiratory
deficiency; characterized by paralysis and hyporeflexia with
or without sensory symptoms
• Affects 1 – 2/100,000
• All ages and genders affected
Guillain-Barre Syndrome
• Etiology
– Believed to be caused by an autoimmune defect
that destroys the myelin sheath of the neuron
– Can have had a history of upper respiratory
infection or flu-like illness preceding onset of
symptoms
– The Epstein-Barr virus may be implicated
Guillain-Barre Syndrome
• Pathophysiology
– Progressive loss of myelin sheath
– Paralysis usually begins in lower extremities with or
without dysesthesia (abnormal sensations from damaged
nerves)
– Progresses upward over hours or days to arms and facial
muscles
– Lower cranial nerves may be affected, leading to drooling,
difficulty swallowing, and/or maintaining an open airway
Guillain-Barre Syndrome
• Pathophysiology
– 30% of patients require ventilatory support
– Generally, spontaneously resolves, though
sometimes with sequelae
– Mortality range of 3 to 6%.
Guillain-Barre Syndrome
• Clinical Findings
– Ascending symmetrical muscle weakness or
paralysis
– Drooling
– Difficulty in speech
– Decreased vital capacity
– Respiratory failure
GB
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RT treatment trach and bronchial hygeine
Mechaincal ventilation
Plasmaphoresis
Protein therapy
Myasthenia gravis
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Myasthenia gravis is a chronic autoimmune neuromuscular disease
characterized by varying degrees of weakness of the skeletal (voluntary)
muscles of the body. The name myasthenia gravis, which is Latin and Greek in
origin, literally means "grave muscle weakness." With current therapies,
however, most cases of myasthenia gravis are not as "grave" as the name
implies. In fact, most individuals with myasthenia gravis have a normal life
expectancy.
The hallmark of myasthenia gravis is muscle weakness that increases during
periods of activity and improves after periods of rest. Certain muscles such as
those that control eye and eyelid movement, facial expression, chewing,
talking, and swallowing are often, but not always, involved in the disorder. The
muscles that control breathing and neck and limb movements may also be
affected.
• http://www.youtube.com/watch?v=YtypsBCjuyQ
Neuromuscular Disorders - Myasthenia
Gravis
• A chronic autoimmune disorder of the neuromuscular junction
characterized by fatigue and weakness, with improvement
following rest
• Sensory function is not lost
• Loss of strength may be confined to an isolated group of
muscles or as a generalized weakness
• Affects 20,000 – 70,000 people in the U.S. annually
• Peak age of onset: females 15-35 yrs, males 40-70yrs
Neuromuscular Disorders - Myasthenia
Gravis
• Etiology
– Thymic tumors are present in 10% of patients
– Antibodies to acetylcholine receptors is seen in
80% of patients
Causes
• Myasthenia gravis is caused by a defect in the transmission of nerve
impulses to muscles. It occurs when normal communication between the
nerve and muscle is interrupted at the neuromuscular junction—the place
where nerve cells connect with the muscles they control. Normally when
impulses travel down the nerve, the nerve endings release a
neurotransmitter substance called acetylcholine. Acetylcholine travels
from the neuromuscular junction and binds to acetylcholine receptors
which are activated and generate a muscle contraction.
• In myasthenia gravis, antibodies block, alter, or destroy the receptors for
acetylcholine at the neuromuscular junction, which prevents the muscle
contraction from occurring. These antibodies are produced by the body's
own immune system. Myasthenia gravis is an autoimmune disease
because the immune system—which normally protects the body from
foreign organisms—mistakenly attacks itself.
Neuromuscular Disorders - Myasthenia
Gravis
• Pathophysiology
– Normally acetylcholine is stored in pre-synaptic
vesicles. it is released into the synaptic space and
binds to the receptor on the post-synaptic
membrane, depolarizing the nerve and leading to
contraction of the muscle
– Binding of cholinesterase to the acetylcholine
receptors blocks the impulse of the nerve,
preventing muscle contraction
Neuromuscular Disorders - Myasthenia
Gravis
• Clinical Findings
– Intermittent weakness of voluntary muscles
– Respiratory symptoms dependent upon severity of
disease
• Upper airway obstruction due to muscle weakness
• Dyspnea on exertion
• Ventilatory failure in severe cases
• Decrease in VC, TLC, IRC, and ERV
• Most deaths occur secondary to pulmonary infections
Symptoms
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Although myasthenia gravis may affect any voluntary muscle, muscles that control
eye and eyelid movement, facial expression, and swallowing are most frequently
affected. The onset of the disorder may be sudden and symptoms often are not
immediately recognized as myasthenia gravis.
In most cases, the first noticeable symptom is weakness of the eye muscles. In
others, difficulty in swallowing and slurred speech may be the first signs. The
degree of muscle weakness involved in myasthenia gravis varies greatly among
individuals, ranging from a localized form limited to eye muscles (ocular
myasthenia), to a severe or generalized form in which many muscles—sometimes
including those that control breathing—are affected. Symptoms, which vary in
type and severity, may include a drooping of one or both eyelids (ptosis), blurred
or double vision (diplopia) due to weakness of the muscles that control eye
movements, unstable or waddling gait, a change in facial expression, difficulty in
swallowing, shortness of breath, impaired speech (dysarthria), and weakness is the
arms, hands, fingers, legs, and neck.
Diagnosis
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Because weakness is a common symptom of many other disorders, the diagnosis of
myasthenia gravis is often missed or delayed (sometimes up to two years) in people
who experience mild weakness or in those individuals whose weakness is restricted
to only a few muscles.
The first steps of diagnosing myasthenia gravis include a review of the individual's
medical history, and physical and neurological examinations. The physician looks for
impairment of eye movements or muscle weakness without any changes in the
individual's ability to feel things. If the doctor suspects myasthenia gravis, several
tests are available to confirm the diagnosis.
A special blood test can detect the presence of immune molecules or acetylcholine
receptor antibodies. Most patients with myasthenia gravis have abnormally elevated
levels of these antibodies. Recently, a second antibody—called the anti-MuSK
antibody—has been found in about 30 to 40 percent of individuals with myasthenia
gravis who do not have acetylcholine receptor antibodies. This antibody can also be
tested for in the blood. However, neither of these antibodies is present in some
individuals with myasthenia gravis, most often in those with ocular myasthenia
gravis.
Diagnosis
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The edrophonium test uses intravenous administration of edrophonium chloride
to very briefly relieve weakness in people with myasthenia gravis. The drug blocks
the degradation (breakdown) of acetylcholine and temporarily increases the levels
of acetylcholine at the neuromuscular junction. Other methods to confirm the
diagnosis include a version of nerve conduction study which tests for specific
muscle "fatigue" by repetitive nerve stimulation. This test records weakening
muscle responses when the nerves are repetitively stimulated by small pulses of
electricity. Repetitive stimulation of a nerve during a nerve conduction study may
demonstrate gradual decreases of the muscle action potential due to impaired
nerve-to-muscle transmission.
Single fiber electromyography (EMG) can also detect impaired nerve-to-muscle
transmission. EMG measures the electrical potential of muscle cells when single
muscle fibers are stimulated by electrical impulses. Muscle fibers in myasthenia
gravis, as well as other neuromuscular disorders, do not respond as well to
repeated electrical stimulation compared to muscles from normal individuals.
Tensilon Test
• http://www.youtube.com/watch?v=k7YX9ku
WrxA