Now let's talk about the diagnosis.
How do we diagnose motor neuron diseases?
Well, first we start with our history.
And this is really important.
There is no diagnostic test that says that
this patient has a motor neuron disease,
we're putting together the symptoms from
the history and the signs from physical exam,
as well as some of our diagnostic
testing to exclude alternative conditions.
First, we want to define the symptoms and
we've talked about some of the symptoms
that are suggestive of upper
and lower motor neuron conditions.
The onset of the disease is often insidious.
There's not a day when the patient develop weakness,
but this slowly develops over the course of months.
It's a chronic onset condition
that develops over time.
We see that typically, motor neuron
diseases progress and they begin chronically
and then progress consistently,
relentlessly steadily over time.
This typically is not rapid though there
are some variants of motor neuron disease
that can progress more rapidly.
But it's typically gradual in its
progression and evolution over time.
We don't see exacerbations on remissions.
In the presence of an exacerbation and
remission such just some alternative etiology,
an autoimmune condition or a paraneoplastic process
or perhaps an infection or occupational exposure.
And this should send us down
an alternative diagnostic workup.
And then there are a host of
symptoms that can affect the patient's life.
And so we want to hear about those symptoms
that would evaluate and establish the diagnosis
as well as to support the patient regardless
of what the diagnosis ends up being.
And then how about on examination, we're
looking at the motor and muscle examination
and patients presenting with weakness from
motor neuron disease, we're looking at muscle bulk
inspecting for atrophy, which we can
see with lower motor neuron lesions,
muscle tone, which we're inspecting for
spasticity or a rigidity that we could see from
an extrapyramidal syndrome.
But spasticity or that clasp knife rigidity
is seen ith upper motor neuron lesions.
We're looking forfasciculations which is very
important in these patients who present with
weakness and muscle
atrophy, to look for fasciculations,
which would be indicative of
a lower motor neuron disease.
And then we're looking at the weakness, patients
typically present with a chief complaint of weakness
and we want to interrogate
what is the distribution.
When we see lower motor neuron symptoms in the
same spinal segment as upper motor neuron symptoms,
that pattern of weakness and findings is
highly suggestive of a motor neuron disease.
And we want to test for proximal weakness
and also look at distal weakness and typically,
motor neuron disorders do not cause a typical proximal
or distal distribution, but both can be involved.
When we're doing the diagnostic exam,
complete neurologic exam is important,
looking at cranial nerves for bulbar involvement,
including tongue atrophy and fasciculations,
looking at the motor and the sensory
exam to exclude sensory findings
and then also reflexes looking for
the presence of upper and/or lower
motor neuron findings on reflex exam
EMG is often performed in these patients.
There's not an EMG signature that establishes
the diagnosis of motor neuron disease,
but we can see findings that are supportive of
this diagnosis and exclude alternative etiologies.
With EMG nerve conduction, we
typically see abnormal electrical signals
in the muscles that are affected
by the motor neuron disease
and this typically is in the
form of reduced amplitude.
There are less motor nerves.
Those motor nerves carry signal and because
there's less of them, we see reduced amplitude,
reduced size of the signal
traveling through that motor nerve.
We can detect spontaneous
depolarization of denervated muscle fibers
as there are loss of nerves innervating the muscle.
The muscles do what they
want, and they fire automatically
and that spontaneous depolarization is
something we can see on our EMG needle exam
and is suggestive of a denervation process.
Importantly, the nerve conduction study is critical
and we're looking at both involvement of motor nerves
and sparing of sensory nerves which is
helping to establish that motor neuronopathy
that motor nerves are the
primary nerves that are involved.
And then lumbar puncture is often performed not
to establish the diagnosis of motor neuron disease,
in which case usually the
lumbar puncture is normal,
but to look for alternative etiologies -
infections, inflammatory disorders or neoplasms
that could masquerade as a motor neuron disease.
Additional laboratory studies to rule out other
causes include a complete metabolic panel.
We talked about the
importance of B12, copper levels,
but B12 and copper deficiency can
present or mimic ALS or motor neuron disease
and HIV antibody testing.
And then MRI is important to
again rule out alternative etiologies.
MRI of the brain and spinal cord
may be important to rule out tumors.
We can look for stroke, inflammatory disorders
that could present similarly infectious syndromes
that affect the brain or the spinal cord and
multiple sclerosis is also an important consideration
in a patient presenting primarily
with an upper motor neuron pathology.
And then let's talk a little bit about the
management of motor neuron diseases.
So in terms of management, there is no standard
treatment for the underlying disease process
for most motor neuron diseases.
And supportive care for the
complications and the symptoms and signs
that we see and can develop in motor neuron disease
must be a primary focus in managing these patients.
First thing we think about is physical therapy.
And stretching and strengthening
exercises to reduce stiffness are critical.
We want to prevent and treat contractures,
that continuous tightening of the muscles
that results in pain and stiffness and and can limit
hygiene and cleaning and those sorts of things.
We want to help improve posture, prevent joint
immobility, slow muscle weakness and atrophy
and there are a number of ways that we
work with physical occupational therapists
and other therapy groups to help
support patients with these symptoms.
Speech therapy is critical for patients
with cortical bulbar involvement.
We want to minimize physical, emotional,
and psychological effects of dysarthria,
dysphasia, which can result in severe
weight loss or nutritional dysfunction,
and speech therapy is important for that.
Speech synthesizers can be used to
enhance and maintain communication
in patients who have lost the ability to speak.
We also think of assistive devices,
mobility aids, canes, wheelchairs, walkers,
motorized wheelchairs, braces and
other orthotics can be helpful for patients
who have an isolated foot
drop or significant weakness or
are paralyzed and and need to support patients.
And these assistive devices are critical in helping
to overcome deficits that develop and persist
And then other therapies are also
important to consider in these patients.
Feeding tubes may be required to maintain
good nutrition in patients with severe dysphasia.
An early initiation of a feeding
tube to maintain nutrition is important
for maintaining patient's physical functioning.
Late initiation of feeding tube does not
improve morbidity or mortality in these patients
and so identifying the right time
to initiate that therapy is important.
In addition, non invasive positive
pressure ventilation or BiPAP and CPAP
or other assistive ventilation devices
can be integrated into the home
for patients with severe
respiratory muscle weakness.
And we often monitor in ALS and motor
neuron disease clinic, respiratory function
gradually over time and
patients who reach a tipping point
where their respiratory muscles
are developing significant weakness
are candidates for home BiPAP and
other limp ventilatory support.
And then what about surgeries?
Surgery doesn't fix the underlying motor neuron
disease but can help patients with symptoms
if the patient has voluntary control of
extremities, lengthening procedures
to get over spasticity and
reduce spasticity or contractures
to increase a patient's level
of function can be considered
for patients that are not
able to use the extremity.
They may need muscle origin release myotomy,
tenotomy, neurectomy or other procedures
to help reduce pain stiffness and other
morbidities from chronic weakness and spasticity.