Neuromuscular Disorders

Question 1

How do lower motor neuron disorders present?

Answer 1

Weak, wasted muscles with low tone
Fasciculations
Reduced/absent reflexes

Question 2

How do upper motor neuron disorders present?

Answer 2

Increased muscle tone

Hyperreflexia

Question 3

What is the motor endplate?

Answer 3

The synapse between the motor neuron and the muscle.

Question 4

What makes up a motor unit?

Answer 4

All the muscle cells attached to a single motor unit.

Question 5

What are 2 examples of presynaptic disorders?

Answer 5

Botulism

Lambert-Eaton Myasthenic Syndrome (LEMS)

Question 6

What causes botulism?

Answer 6

Food poisoning or another route in which the patient is contaminated with botulinum toxin.

Risk in PWIDs taking heroin.

Question 7

How does botulinum toxin cause disease?

Answer 7

It cleaves presynaptic proteins that are involved in vesicle production.

It blocks docking of vesicles onto the presynaptic membrane.

Question 8

What features present in botulism?

Answer 8

Rapid onset motor weakness with NO sensory loss. Produces an ascending paralysis.

Question 9

How is botulism treated?

Answer 9

Supportively only. The patient will recover after 12 weeks.

Beware risk of respiratory failure.

Question 10

What produces disease in LEMS?

Answer 10

Production of antibodies that act against presynaptic Ca2+ channels, affecting the release of vesicles.

Question 11

What form of cancer is linked to LEMS?

Answer 11

Squamous cell carcinoma

LEMS is a paraneoplastic syndrome.

Question 12

How is LEMS treated?

Answer 12

3-4, diaminopyridine

Question 13

What is an example of a postsynaptic disorder?

Answer 13

Myasthenia gravis

Question 14

What pathology underlies myasthenia gravis?

Answer 14

An autoimmune condition involving antibodies against acetylcholine receptors. This results in reduced functional receptors.

Question 15

What features are seen in myasthenia gravis?

Answer 15

Muscle weakness

Fatiguability

Question 16

Bilateral facial weakness is a hallmark of which NMJ disorder?

Answer 16

Myasthenia gravis

Patient will not be able to smile.

Question 17

Symptoms present at which % of receptor involvement in myasthenia gravis?

Answer 17

Around 30%.

Question 18

Which age group are most affected by myasthenia gravis?

Answer 18

3rd decade (usually female)
6/7th decade (mostly male)

This has 2 peaks.

Question 19

In early disease, which muscles are affected?

Answer 19

Intraocular muscles
Facial muscles
Bulbar muscles

Question 20

What tests are used to diagnose myasthenia gravis?

Answer 20

Antibody test (90% specific)
EMG (2nd line)

Question 21

Is the thymus linked to myasthenia gravis?

Answer 21

Yes, 75% will have hyperplasia or thymoma.

Question 22

How is myasthenia gravis treated?

Answer 22

Pyridostigmine (anticholinesterase inhibitor) - given if ocular only ACUTE
IV immunoglobulin - if generalised ACUTE
Thymectomy
High-dose steroids

Question 23

How is MG treated in an emergency?

Answer 23

Plasma exchange

Question 24

Which antibiotic aggravates myasthenia gravis and should be avoided at all costs?

Answer 24

Gentamicin

Question 25

What is myotonia?

Answer 25

Failure of muscle relaxation following use.

Patient will not release a hand-shake.

Question 26

What is polymyositis?

Answer 26

A symmetrical, proximal muscle disease of progressive nature.

It is treated with steroids.

Question 27

What % of dermatomyositis patients have underlying malignancy?

Answer 27

Around 50%.

Question 28

What is the most common muscular dystrophy?

Answer 28

Myotonic dystrophy

An autosomal dominant disorder involving a trinucleotide repeat.

Question 29

What is rhabdomyolysis?

Answer 29

The dissolution of muscle.

It can be fatal.

Question 30

What is the triad of symptoms seen in rhabdomyolysis?

Answer 30

Myalgia
Muscle weakness
Myoglobinuria

Question 31

How is rhabdomyolysis treated?

Answer 31

ITU - supportive care only.