In this lecture, we're going to learn about
infections of the neuromuscular junction.
It's a really neat topic,
not commonly encountered in patients,
but seen in clinical vignettes
and just a really cool
list of disorders.
Let's start with the case.
This is a 72-year-old woman
who presented with weakness.
This 72-year-old woman had Parkinson's
disease and presented for management
of right foot & leg dystonia
related to the Parkinson's disease.
She had been receiving botulinum
toxin type A for about a year
to treat this spasticity
increased tone in this leg
and she returned for
She presented for her fifth injection
of botulinum toxin with 600 total units,
which is standard for a limb into
the muscles of the right leg.
Three days after the treatment,
she developed right leg heaviness.
One week later, she developed
diplopia, dysphagia and head drop.
Her pupils were dilated and poorly
reactive with intact extraocular movements.
Examination showed 4/5 weakness of
the bilateral proximal arm muscles,
reduced neck flexion and
1+ deep tendon reflexes,
so slightly reduced deep tendon
reflexes throughout the entire body.
Sensory exam was normal.
A nerve conduction study with repetitive
nerve stimulation showed a 14% decrement
with 3-Hz stimution that was recovered
after 1 minute of maximal exercise.
With 10 seconds of voluntary muscle exercise,
no incremental response was observed
and acetylcholine receptor
antibody testing is negative.
So a long case,
some important features.
What's the diagnosis?
Let's walk through some of
the key findings in this case.
And let's think about the distribution,
sensory findings and reflex exam,
as well as any wildcard symptoms,
that could point us to the localization
for this peripheral
nervous system complaint.
First of all,
in terms of the distribution
this patient presents
with proximal weakness.
there are prominent bulbar symptoms.
This patient has diplopia and ptosis
and problems with bulbar function.
This entry exam is normal which
points us away from a nerve problem
and towards muscle or
and specifically neuromuscular
junction, in this case.
The Reflex exam so
slightly reduced reflexes,
which we can see from a neuromuscular
junction disorder, but not absent.
And there's some
she developed the diplopia,
dysphagia and head drop first
and this was followed
by generalized weakness.
And that time course and
progression of symptoms
is important in
evaluating this patient.
This patient had repetitive nerve stimulation
and let's look specifically at that.
In this table, repetitive stimulation
is where we shocked the nerve
and look at muscle contraction
serially over time.
This is 3-Hz stimulation,
so 3 stimulations every 1 second.
With the first
stimulation of the nerve,
we can look at the amount of contraction,
the amplitude of the muscle response
and we see that the
amplitude was 2.2.
A good muscle contraction as a
result of that first stimulation.
And then with successive stimulations,
we see that the amplitude drops.
The amount of muscle
contraction goes down
even though we're sending just
as much signal through the nerve.
So the amplitude goes down to
1.96, .94, .84, .89, .85, .77
and we see a
The same nerve stimulation,
results in less muscle activation,
less muscle contraction,
less end-plate potential depolarization,
to a maximum of 20%.
So what's the diagnosis?
Is this seropositive myasthenia?
Botulinum toxin toxicity?
or Organophosphate poisoning?
Well, this doesn't sound
like myasthenia gravis.
We see pupillary involvement, which we
said we don't see with myasthenia gravis.
The symptoms started
proximally in the bulbar fibers
and then move distally to involve weakness,
and that progression is a typical.
Typically, Myasthenia starts with
weakness and then potentially the presence
and likely the presence
of bulbar symptoms.
The patient has no history or signs
of taking prior again a phosphates
or an ingestion of some kind,
poisoning is not supported
by the case presentation.
There was no testing
for, excuse me,
a testing for acetylcholine
receptors was negative in this case.
So that's inconsistent with a diagnosis
of Seropositive myasthenia gravis.
And so this is a good
example of a patient
who was diagnosed with
following botox toxin injection.
And the things to note
about this case for the
prominent pupillary involvement,
involvement of autonomics,
which is very specific
for botulism toxicity
and prominent proximal weakness
spreading proximally to distally.