00:01
In this lecture, we're going
to talk about
neuromuscular junction
disorders.
00:05
A neat group of disorders that are
really important to understand
for both patients and when answering
clinical vignettes.
00:14
As you recall, whenever
we're evaluating anyone
who presents with some type
of neurologic complaint,
we break it down.
00:21
And the first thing we have
to figure out is whether this is
a central nervous system problem,
or a peripheral
nervous system problem.
00:28
And we use things
like the neurologic exam
to localize the
patient's presentation
to the CNS, or the PNS.
00:36
In the peripheral nervous system,
there's really three places
that we consider
for most presentations.
00:41
We want to figure out,
could this be coming
from the muscle,
the neuromuscular junction,
and the nerve?
And we use our history,
in particular our examination,
to localize the problems
to a specific area
of the peripheral nervous system.
00:56
In the neuromuscular junction,
we can further subdivide
diseases and presentations
into those that
are presynaptic,
occurring at the
presynaptic terminus
of the neuromuscular junction,
or postsynaptic.
01:08
And that's an important way
that we walk through problems
in the peripheral nervous system.
01:14
So let's think more specifically
about the neuromuscular junction.
01:17
How do we localize problems
to the neuromuscular junction
and focus in on pathology
in that area?
When we use our
neurologic exam,
we always perform a comprehensive
neurologic exam.
01:29
But when we're worried about a
problem at the junction,
I want you to think of three things
and focus on those
three parts of the history
and the physical examination.
01:37
We're going to learn
that the distribution of the
patient's symptoms is key
to honing in on the
neuromuscular junction
and differentiating from muscle or
peripheral nerve pathology.
01:48
We're going to look for
sensory findings
and sensory symptoms
and that will be
a helpful differentiator
between the peripheral nerve
and the neuromuscular junction.
01:56
We're also going to
focus on reflexes.
01:57
And reflexes are
critically important
when evaluating these patients.
02:01
For neuromuscular junction diseases,
as you'll see,
there's a characteristic
distribution.
02:07
Patients can have proximal weakness
or distal weakness.
02:10
But the key finding,
the key distribution
is we see bulbar symptoms.
02:15
Patients have ptosis, diplopia,
dysarthria, dysphasia,
or some combination of those.
02:20
And you'll see
in the image on the right,
this patient with right sided ptosis
and the presence of bulbar findings
is critical
for localizing a problem
to the neuromuscular junction,
and in particular differentiating
from muscle disease.
02:34
For junctional disorders,
we typically see
that sensory findings are absent.
02:38
Patients don't have paraesthesias.
02:41
There's not numbness, or
paraesthesia, or tingling,
or those sorts of symptoms,
and we don't find those on exam.
02:49
Our reflex examination often reveals
normal reflexes
or slightly reduced reflexes.
02:55
Importantly, we don't tend to see
absent reflexes
with most neuromuscular
junction disorders.
03:01
And then with each of these
peripheral nervous system
localizations
there's a wildcard
some neat important
other criteria
that can help focus in,
and hone in
on a problem in this area.
03:13
And for the neuromuscular junction,
we think about fatigable weakness.
03:17
Presence of symptoms
that get worse through the day,
or worse with prolonged activity,
that fatigability of symptoms is
going to point us in the direction
of the neuromuscular junction.
03:28
So let's take a look at the junction
and see what we're talking about.
03:32
This is the connection between the
nerve and the muscle,
where electrical signals
and an action potential
are converted to chemical signals
in the synaptic cleft.
03:40
And when we're localizing this
conditions in this area,
we think of the
presynaptic problems,
and the postsynaptic problems.
03:47
Some of those that
we'll learn about,
we'll learn about botulism.
03:51
This is a presynaptic disorder that
affects the neuromuscular junction
and presents with
junctional weakness.
03:57
Lambert-Eaton myasthenic syndrome
is also a presynaptic disorder
affecting the calcium channels
on the presynaptic terminus.
04:06
In the postsynaptic area,
we think of myasthenia gravis.
04:09
And this is a critical disorder.
04:10
One of the most common
neuromuscular junction conditions
and it affects the
postsynaptic terminus.