Lambert Eaton Myasthenic Syndrome Flashcards
What is Lambert-Eaton myasthenic syndrome?
It is defined as an autoimmune condition in which the immune system targets the presynaptic voltage-gated calcium channels in the peripheral nervous system
What occurs at the neuromuscular junction?
Motor nerves communicate with the muscles
Describe the process that occurs at the neuromuscular junction that leads to muscular contraction
At the neuromuscular junction, the axons of the motor nerves are situated across a synapse from the post-synaptic membrane of the muscle cell
The voltage gated calcium channels enable the release of a neurotransmitter, known as acetylcholine, from the pre-synaptic membrane which then travels across the synapse and attaches to the receptors on the post-synaptic membrane
This causes receptor stimulation, leading to muscle contraction
Describe the pathophysiology of Lambert Eaton myasthenic syndrome
There are presynaptic voltage gated calcium channel antibodies are produced by the immune system
This results in destruction of these calcium channels, thus prevents the binding of acetylcholine and therefore muscle contraction
What are the three risk factors of Lambert Eaton myasthenic syndrome?
Small Cell Lung Cancer
Breast Cancer
Ovarian Cancer
What is the main risk factor of Lambert-Eaton myasthenic syndrome?
Small cell lung cancer
What is the characteristic clinical feature of Lambert-Eaton myasthenic syndrome?
Muscle fatiguability
This is when muscles become progressively weaker during periods of activity and slowly improve after periods of rest
This usually means that clinical features are minimal in the morning and worse at the end of the day
What are the other seven clinical features of Lambert-Eaton myasthenic syndrome?
Proximal Muscle Weakness
Hyporeflexia
Diplopia
Ptosis
Dysphagia
Slurred Speech
Dry Mouth
What are two clinical features that differentiate Lambert-Eaton myasthenic syndrome and myasthenia gravis?
In Lambert-Eaton myasthenic syndrome, the proximal muscles are usually affected first. In some cases, repeated muscle contractions can lead to increased muscle strength
In myasthenia gravis, the distal muscles are usually affected first. In all cases, repeated muscle contractions can lead to decreased muscle strength
What is the investigation used to diagnose Lambert-Eaton myasthenic syndrome?
Electromyography (EMG)
What is EMG?
It is a test that measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle
What is the feature of Lambert-Eaton myasthenic syndrome on EMG?
There is an incremental response to repetitive nerve stimulation
Once a diagnosis of Lambert-Eaton myasthenic syndrome has been confirmed, what other investigations should be conducted?
In cases where individuals don’t have a pre-existing diagnosis of small cell lung cancer, this would be investigated to determine whether it is the underlying aetiology
What are the four pharmacological management options of Lambert-Eaton myasthenic syndrome?
Potassium Channel Blockers
Immunosuppression
IV Immunoglobulins
Plasmapheresis
What is the function of potassium channel blockers? How are they used to manage Lambert-Eaton myasthenic syndrome?
They block voltage gated potassium channels in the presynaptic cells, prolonging the depolarisation of the cell membrane and enabling increased action of the calcium channels
This results in an increased release of acetylcholine within the neuromuscular junction synapses
