Neurology - Lambert Eaton Myasthenic syndrome

Question 1

What is Lambert Eaton Myasthenic syndrome?

Answer 1

Presents similarly to MG

It causes progressive muscle weakness with increased use as a result of damage to the neuromuscular junction.

The symptoms tend to be more insidious and less pronounced than in myasthenia gravis.

Question 2

What is Lambert-Eaton associated with?

Answer 2

Small-cell lung cancer

Question 3

What causes Lambert-Eaton?

Answer 3

It is a result of antibodies produced by the immune system against the voltage-gated calcium channels in small cell lung cancer (SCLC) cells.

These antibodies also target and damage voltage-gated calcium channels in the presynaptic terminals of the NMJ

Calcium channels in the NMJ assist the release of ACh which is the neurotransmitter and is required for muscle contraction

Question 4

Presentation of Lambert-Eaton

Answer 4

Slow onset

Proximal muscles most notably affected

Most notably presents with proximal leg muscle weakness

Can also cause:

• Diplopia (weakness of intraocular muscles)
• Ptosis (levator muscle)
• Slurred speech and swallowing difficulties (oropharyngeal muscles)

Also can cause autonomic dysfunction symptoms of dry mouth, blurred vision, impotence and dizziness

Question 5

Examination findings

Answer 5

Fatigable weakness as in MG

BUT ALSO:

• Reduced tendon reflexes
• A notable finding is that these reflexes become temporarily normal for a short period following a period of strong muscle contraction.
• For example, the patient can maximally contract the quadriceps muscle for a period, then have their reflexes tested immediately afterwards, and display an improvement in the response.
• This is called post-tetanic potentiation.

Question 6

Management of Lambert Eaton

Answer 6

Diagnosis and management of underlying malignancy

Investigate for small cell lung cancer

Amifampridine - allows more acetylcholine to be released in the neuromuscular junction synapses.
- It works by blocking voltage-gated potassium channels in the presynaptic cells, which in turn prolongs the depolarisation of the cell membrane and assists calcium channels in carrying out their action

Other options include immunosuppressants e.g. prednisolone, azathioprine, IVIG, plasmapheresis