Neuromuscular Disorders Flashcards
How do lower motor neuron disorders present?
Weak, wasted muscles with low tone
Fasciculations
Reduced/absent reflexes
How do upper motor neuron disorders present?
Increased muscle tone
Hyperreflexia
What is the motor endplate?
The synapse between the motor neuron and the muscle.
What makes up a motor unit?
All the muscle cells attached to a single motor unit.
What are 2 examples of presynaptic disorders?
Botulism
Lambert-Eaton Myasthenic Syndrome (LEMS)
What causes botulism?
Food poisoning or another route in which the patient is contaminated with botulinum toxin.
Risk in PWIDs taking heroin.
How does botulinum toxin cause disease?
It cleaves presynaptic proteins that are involved in vesicle production.
It blocks docking of vesicles onto the presynaptic membrane.
What features present in botulism?
Rapid onset motor weakness with NO sensory loss. Produces an ascending paralysis.
How is botulism treated?
Supportively only. The patient will recover after 12 weeks.
Beware risk of respiratory failure.
What produces disease in LEMS?
Production of antibodies that act against presynaptic Ca2+ channels, affecting the release of vesicles.
What form of cancer is linked to LEMS?
Squamous cell carcinoma
LEMS is a paraneoplastic syndrome.
How is LEMS treated?
3-4, diaminopyridine
What is an example of a postsynaptic disorder?
Myasthenia gravis
What pathology underlies myasthenia gravis?
An autoimmune condition involving antibodies against acetylcholine receptors. This results in reduced functional receptors.
What features are seen in myasthenia gravis?
Muscle weakness
Fatiguability
Bilateral facial weakness is a hallmark of which NMJ disorder?
Myasthenia gravis
Patient will not be able to smile.
Symptoms present at which % of receptor involvement in myasthenia gravis?
Around 30%.
Which age group are most affected by myasthenia gravis?
3rd decade (usually female) 6/7th decade (mostly male)
This has 2 peaks.
In early disease, which muscles are affected?
Intraocular muscles
Facial muscles
Bulbar muscles
What tests are used to diagnose myasthenia gravis?
Antibody test (90% specific) EMG (2nd line)
Is the thymus linked to myasthenia gravis?
Yes, 75% will have hyperplasia or thymoma.
How is myasthenia gravis treated?
Pyridostigmine (anticholinesterase inhibitor) - given if ocular only ACUTE
IV immunoglobulin - if generalised ACUTE
Thymectomy
High-dose steroids
How is MG treated in an emergency?
Plasma exchange
Which antibiotic aggravates myasthenia gravis and should be avoided at all costs?
Gentamicin
What is myotonia?
Failure of muscle relaxation following use.
Patient will not release a hand-shake.
What is polymyositis?
A symmetrical, proximal muscle disease of progressive nature.
It is treated with steroids.
What % of dermatomyositis patients have underlying malignancy?
Around 50%.
What is the most common muscular dystrophy?
Myotonic dystrophy
An autosomal dominant disorder involving a trinucleotide repeat.
What is rhabdomyolysis?
The dissolution of muscle.
It can be fatal.
What is the triad of symptoms seen in rhabdomyolysis?
Myalgia
Muscle weakness
Myoglobinuria
How is rhabdomyolysis treated?
ITU - supportive care only.
