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in this lecture
we're going to talk about neuromuscular
junction disorders
a neat group of disorders that are
really important to understand
for both patients and when answering
clinical vignettes
as you recall whenever we're evaluating
anyone who presents with some type of
neurologic complaint
we break it down and the first thing we
have to figure out is whether this is
a central nervous system problem or a
peripheral nervous system problem
and we use things like the neurologic
exam to localize the patient's
presentation
to the cns or the pns in the peripheral
nervous system there's really three
places that we consider for most
presentations
we want to figure out could this be
coming from the muscle the neuromuscular
junction
and the nerve and we use our history and
in particular our examination
to localize the problems to a specific
area
of the peripheral nervous system 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 and that's an important
way that we
walk through problems in the peripheral
nervous system
so let's think more specifically about
the neuromuscular junction
how do we localize problems to the
neuromuscular junction
and focus in on pathology in that area
well we use our neurologic exam and we
always perform a comprehensive
neurologic exam
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 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 we're
going 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
we're also going to focus on reflexes
and reflexes are critically important
when evaluating these patients
for neuromuscular junction diseases as
you'll see there's a characteristic
distribution
patients can have proximal weakness or
distal weakness
but the key finding the key distribution
is we see bulbar
symptoms patients have ptosis diplopia
dysarthria
dysphagia or some combination of those
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
for junctional disorders we typically
see that sensory findings are absent
patient don't patients don't have
paresthesias
there's not numbness or paresthesias or
tingling
or those sorts of symptoms and we don't
find those on exam
our reflex examination often reveals
normal reflexes or
slightly reduced reflexes importantly
we don't tend to see absent reflexes
with most
neuromuscular junction disorders and
then with each of these peripheral
nervous system localizations there's a
wild card
some neat important other criterion
that can help focus in and hone in on a
problem in this area
and for the neuromuscular junction we
think about fatigable weakness
presence of symptoms that get worse
through the through the day or worse
with
prolonged activity that fatigability of
symptoms is going to point us in the
direction
of the neuromuscular junction so let's
take a look at the junction
and see what we're talking about 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
and when we're localizing the conditions
in this area
we think of the presynaptic problems and
the postsynaptic problems
some of those that we'll learn about
we'll learn about botulism
this is a pre-synaptic disorder that
affects the neuromuscular junction
and presents with junctional weakness
lamberton myasthenic syndrome is also a
presynaptic disorder
affecting the calcium channels on the
presynaptic terminus
in the postsynaptic area we think of
myasthenia gravis and this is a critical
disorder one of the most common
neuromuscular junction conditions
and it affects the postsynaptic terminus
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you