So what's the typical
work up for a patient,
who were concerned may have
Lambert-Eaton myasthenic syndrome?
Well, we've talked about
nerve conduction studies
and that's critical of for evaluating
the neuromuscular junction.
For looking at the nerve, at the
muscle and how they're communicating.
The nerve conduction study for
Lambert-Eaton myasthenic syndrome
may show neuropathic findings.
And this is a typical because
it's not a nerve condition,
but we can see those findings.
We look for three things in the
nerve conduction study for a
The first is Reduced CMAP Amplitude-
compound muscle action potential,
reduced action of the muscle.
We can see a
with low frequency
stimulation 3-Hz stimulation.
And this is indicative of a
neuromuscular junction disorder.
We see the same decremental
response or can see this response
with any neuromuscular
And then importantly the 3rd
point here is really important.
We see an incremental response
with high-frequency stimulation.
This is unique to
and it is diagnostic of a
presynaptic junctional disorder.
An incremental response with high
frequency repetitive nerve stimulation.
This is an immune mediated condition,
so we look for those immune cells
and lab testing should include.
Tests for voltage-gated calcium
channel antibodies in the serum.
And this is commonly
seen in these patients.
And then it's associated with cancer,
so we need to screen for cancer.
And we do prod widespread cancer screening,
but particularly look for lung cancers
or possible lymphomas, which are
most associated with this condition.
Let's focus more on the nerve conduction
testing for Lambert-Eaton syndrome.
Repetitive nerve stimulation is key to
evaluating a neuromuscular junction disorder,
and we're looking for two
findings that are both sensitive
and specific for a diagnosis
of Lambert-Eaton syndrome.
The first is we see a decrement
in the CMAP amplitude-
the compound motor
a decrement in the response of greater
than 10% with low frequency stimulation.
With 3-Hz stimulation, we see that
decrement in the signal that transfers
from the nerve to the muscle and
the contraction of the muscle.
Importantly the second finding that is
diagnostic of lambert-eaton syndrome
or a presynaptic terminals
problem is an incremental response
with fast or fast hertz
So we see an increment in the CMAP
amplitude of greater than a hundred percent
at high-frequency stimulation
or with post exercise testing.
This incremental response is due
to increased release of calcium
as a result of
We're overriding those
we're driving acetylcholine
into the presynaptic terminus
and release into
the synaptic cleft
and allowing that muscle to contract
even more than it did, at baseline.
In terms of serologic testing we test for the
voltage-gated calcium channel antibodies.
Those are PQ type voltage-gated
calcium channel antibodies
and testing should be performed in all
patients suspected of Lambert-Eaton syndrome.
We see these antibodies in about 85
to 90% of patients who have limbs.
So the presence of a voltage
gated calcium channel antibody
in someone who has weakness
and a concern for cancer
is diagnostic of
is also important,
and here's the chest CT for
the patient from our case.
We do both chest x-rays and chest CT's
to look for findings of a lung cancer
and particularly a
small cell lung cancer
and may also need to do screening
for Lymphoma or other cancers,
if our initial workup
for cancer is negative.
And here you can see a large
lesion in the right lobe
of the lung highlighted
by this green arrow
that in this patient with
rapid weight loss is consistent
or concerning for a diagnosis of cancer and
would be biopsied for further evaluation