So let's look a little bit closer at the
pathophysiology of Lambert-Eaton syndrome.
What's going on at the level
of the neuromuscular junction?
Well, as we said,
the condition is characterized by
voltage-gated calcium channel antibodies.
These antibodies bind to that calcium
channel on the presynaptic terminus
and prevent calcium from
coming into the terminus
and allowing acetylcholine to be
released into the synaptic cleft.
release leads to a decrement,
a decrease in the
baseline motor amplitude.
The baseline contraction of the
muscle at that neuromuscular junction.
Quant chronic reduced
acetylcholine quanta release
results in increased
So the neuromuscular junction
recognizes that there's a problem
and there's increased folding
of the postsynaptic membrane.
With slow repetitive
there's a decremental response.
And this is owing to the fact that there is
a reduction in the amount of acetylcholine
that's released into
the synaptic cleft.
But with fast repetitive stimulation
or 1 minute of forced maximal exercise,
there's a build up of calcium that
occurs in the presynaptic terminus.
You get a lot of
calcium, you overwhelm
those voltage gated calcium receptors
are voltage-gated calcium channels.
And in this setting,
there's increased postsynaptic folding
and this results in an
More acetylcholine is
released into the cleft.
There is more postsynaptic folding
and more acetylcholine receptors
and this results in
Let's look at that pictorially
in this graph here.
So here we see
There's an action potential that activates
the voltage-gated calcium channels
in the presynaptic terminus.
Calcium is in flux
into the terminus,
this allows the vesicles
containing acetylcholine to be,
bind to the
Acetylcholine is released,
and there's activation of the muscle
What happens in the
In the pathologic state,
there's still an action potential
but those voltage-gated calcium
channels can be activated.
binding preventing calcium
from in fluxing into
the nerve terminus,
and as a result,
you see less acetylcholine released
and less muscle activation
What about with treatment?
We're going to talk in the next slide about
some of the treatments for this condition,
and 1 is this agent called
And this is a drug that acts
on the presynaptic terminus
to prolong the time
of calcium influx.
And so even though there's less
influx with each action potential
it prolongs the time of in flux
increases the amount of vesicles
that bind the
and you get more acetylcholine
in the cleft and more likely
see muscle contraction and
So what are the treatments for
Lambert-Eaton myasthenic syndrome?
we've tried a number of things.
Corticosteroids can be used to reduce
the amount of circulating immune cells.
Those voltage-gated calcium
channel antibodies that we see.
Guanidine has been tested,
is a neat medicine that is approved and
used for the treatment of this condition.
It acts on potassium channels
in the presynaptic terminus.
It prolongs the time of calcium channel
in flux in the presynaptic terminus,
increases the likelihood that those
synaptic vesicles will bind to the membrane
and release their
And so it can improve muscle contraction and
connection at the neuromuscular junction.
This is also an immune mediated
condition and so Plasmapheresis
and intravenous immunoglobulin can
be used to remove those antibodies
from systemic circulation and
improve patients symptoms.
this is associated with cancer
and it occurs as a result of the
immune response to the cancer.
Treatment of cancer is critical.
When the cancer is treated
and put into remission,
the immune response dies down in many
patients see improvement in their symptoms.