Now let's talk about the clinical
manifestation of motor neuron diseases.
How do patients present?
What are their signs and what
are some of the symptoms?
Well, we can see upper motor neuron
signs and the typical clinical manifestations of
upper motor neuron pathology,
are demonstrated here.
We can see weakness, weakness can come
from a problem of any of the motor nerves -
primary motor neuron, the upper motor
neuron, or the secondary motor neuron,
the peripheral lower motor neuron.
We can see increased tone, and spastic tone is
a classic sign of upper motor neuron pathology.
Sspasticity is what we see in evaluating tone when
we look at passive range of motion of the muscles.
Hyperreflexia is a classic sign of upper motor neuron
We don't see fasciculations.
Fasciculations suggest lower motor
neuron pathology, so we don't see that
from upper motor neuron disorders.
And we can see rigidity, it's
often a clasp, knife rigidity,
which is really spastic tone that we're seeing.
Spasticity is both velocity and angle dependence.
And so the faster you move
the limb with passive movement,
the more tone there is, and so when you're
moving really quickly, there's a lot of tone.
When you're moving slowly,
there's relatively less tone.
It's also angle dependent.
We see that that increase in tone is more severe
out of extension, and less severe in at flexion.
And so those are features of clasp-knife
rigidity, and suggestive of spasticity
are a problem with the upper motor neurons,
the pyramidal system, they're pyramidal findings.
Clonus is a significant
hyperreflexia, 4+ hyperreflexia
where there's sustained
beating of a deep tendon reflex,
and the Babinski sign or an
extensor plantar response is indicated,
is an indicator of upper motor neuron pathology.
What about upper motor neuron bulbar symptoms?
This has been coined pseudobulbar
palsy, which is those same
upper motor neuron dysfunction and
disorders affecting the corticobulbar fibers.
We can see slurred speech, dysphasia, a
spastic dysarthria where there's really stiffening
of the vocal cords and oral pharyngeal muscles,
tongue spasticity, reduced mobility of the tongue,
both with protrusion or
lateral side to side movements.
pseudobulbar affect is emotional lability.
It's a spastic emotion where patients
have really high highs and really low lows.
They cry when they're not sad,
they laugh when they're not happy.
And that emotional lability is that same
spasticity that we see in the motor nerves,
but here we're seeing him in emotional control.
And that's likely due to motor control of the
face, unprovoked crying, laughing and anger.
We can see a hyperactive gag reflex and a jaw jerk.
And typically, with a patient modestly
or minimally opening their mouth
and we tap on the jaw with a reflex hammer,
we don't see much in the way of a jerk of the jaw.
And in upper motor neuron disorders tapping
on the jaw results in an intense biting jaw jerk
which is indicative of upper motor neuron
signs or upper motor neuron pathology
of the corticobulbar fibers.
We can also see lower motor neuron
dysfunction in motor neuron disorders.
And here are some of the clinical manifestations
we can see from lower motor neuron dysfunction.
Again, weakness we can see from problems
with any of the motor nerves, upper or lower.
Atrophy is very common with
lower motor neuron pathology.
Fasciculations are really important.
They are pathognomonic for
lower motor neuron dysfunction.
These are visible involuntary
contractions of a single motor unit.
That's a motor nerve and all of the
muscles that innervates and it looks like
the patient is moving their
muscle but with it relaxed.
It's very important when
evaluating for fasciculations.
The patient is relaxed, all the muscles
are still and and you're looking for
involuntary contraction of a
muscle group, which is a fasciculation
and typically it looks like
an undulation of the muscle.
We can see decreased tone from lower
motor neuron pathology and hyporeflexia.
In addition, we can see lower motor neuron
signs affecting the corticobulbar fibers.
We can see dysfunction in any area of the
brainstem but frequently we can see and look
for pathology affecting the
medullary region of the brainstem.
Cranial nerves IX, X, XI and XII -
we can see impairment in chewing,
swallowing and tongue movements
Tongue fasciculations and atrophy are one of
the pathognomonic signs for motor neuron disease.
It's important that we look for tongue
fasciculations and atrophy in patients suspected
of motor neuron disorders and this is
done by having the patient open their mouth
and looking at the tongue
in the relaxed and passive condition.
Protruding the mouth can cause the tongue to move
and fasiculate, so we're really looking at passive
a still position of the tongue
to look for tongue fasciculations.
Diminished gag reflex and a jaw jerk
that's normal or absent is also suggestive of
lower motor neuron dysfunction
of those corticobulbar fibers.
So let's compare some of the clinical findings with
upper motor neuron and lower motor neuron lesions.
Knowing that with motor neuron
diseases sometimes we see a combination
of upper and lower motor neuron pathology.
First, we look for muscle tone.
With upper motor neuron lesions, we see
spastic tone, increased tone, clasp-knife rigidity,
and with lower motor neuron
lesions, patients become hypotonic.
In terms of muscle mass, with classic upper
motor neuron lesions, there's often no change
though with long term upper motor neuron
lesions, we can see a little bit of atrophy.
But with lower motor neuron lesions, we
see prominent muscle wasting and atrophy
that is particularly prominent on exam.
We need to look for fasciculations, we don't see
fasciculations in pure upper motor neuron lesions,
but we do when there's
lower motor neuron pathology.
Deep tendon reflexes, we see
hyperreflexia with upper motor neuron lesions,
hypo/areflexia with lower motor neuron lesions, and
this is important
Areflexia, should point us squarely
towards a peripheral nerve dysfunction
and particularly the lower motor neuron.
And then on EMG, we typically see
normal nerve conduction testing with
pure upper motor neuron lesions
and abnormal conduction , reduced
amplitude of the compound motor action potential,
the motor potential with lower motor neuron
Importantly, there is not a diagnostic test
that says that this is a motor neuron disorder
and we're using our clinical
exam, the symptoms, the signs and
in some cases EMG nerve conduction
to support that diagnosis in these patients.