Disorders of Neuromuscular Transmission

Question 1

Autoimmune disorder that results in a pure motor syndrome

Characteristic muscular weakness

Answer 1

Myasthenia Gravis

Question 2

What is the pathophysiology of myasthenia gravis?

Answer 2

Variable degree of block of neuromuscular transmission caused by
autoantibodies binding to the acetylcholine receptors

Reduces the number of functioning receptors

Question 3

What are factors that can exacerbate myasthenia gravis?

Answer 3

Pregnancy

Prior to menstrual cycle

Infections

Question 4

What is the most common demographic for myasthenia gravis?

Answer 4

Most common in young females
typically 20-40 years

Question 5

What disease Presents as:

fluctuating weakness of commonly used voluntary muscles

Activity increases weakness of affected muscles

Worsens in the morning

Answer 5

Myasthenia Gravis

Question 6

Myasthenia gravis can be associated with which condition(s)?

Answer 6

Thyrotoxicosis

Thymic tumor (more common in older men)

Rheumatoid arthritis

Lupus erythematosus

Question 7

What muscles are affected in Myasthenia gravis?

Answer 7

Extraocular
pharyngeal and facial
proximal limbs
respiratory musculature

Question 8

What is a Myasthenia crisis?

Answer 8

When the disorder of myasthenia gravis is sometimes unmasked by a coincidental infection that leads to exacerbation of symptoms

Life threatening exacerbation of myasthenia gravis (can lead to respiratory weakness)

Question 9

Name some signs and symptoms of myasthenia gravis?

Answer 9

Diplopia (25%)

Ptosis (25%)

Facial weakness

Difficulty chewing/fatigue with chewing

Difficulty swallowing (10%)

Respiratory difficulties/weakness

Limb weakness/proximal limbs

Dysarthria (10%)

Dysphonia

Neck weakness

Generalized weakness (10%) chewing/fatigue

Question 10

What is important to remember in myasthenia gravis?

Answer 10

Sensation is normal!

Question 11

How can you diagnose myasthenia gravis?

Answer 11

Acetylcholine receptor antibody assay (Sensitivity of 80-90% for diagnosis)

Short-acting anticholinesterases transiently improve the weakness

Electrophysiology studies - EMG or single fiber EMG (Sensitivity of 50% for diagnosis)

Question 12

What disease is described below?

May be associated with small cell lung cancer
Defective release of acetylcholine in response to a nerve impulse (Leads to weakness, especially in proximal muscles of limbs)
Muscle strength increases with repetitive stimulation

Answer 12

Myasthenia Syndrome

Question 13

In Myasthenia Syndrome, which muscles are most affected?

Answer 13

proximal muscles of limbs

Question 14

What disorder of neuromuscular transmission is a toxin that prevents the release of acetylcholine at neuromuscular junction and autonomic synapses

Answer 14

Botulism

Question 15

What is the causative organism in Botulism?

Answer 15

Clostridium Botulinum

Question 16

What history is typical of Botulism?

Answer 16

look for history of canned food (typically ingested)

Question 17

What is the presentation of Botulism?

Answer 17

Presents with sudden, fluctuating severe weakness that may worsen
over several days
Sensation and reflexes will be preserved
Symptoms occur 72 hours after ingestion

Question 18

What are signs and symptoms of Botulism?

Answer 18

Blurred vision
Diplopia
Ptosis
Facial weakness
Dysphagia
Nasal speech
Respiratory difficulty (in severe cases)
Weakness in limbs
May have constipation and postural hypotension

Question 19

Does Botulism require notification to a local health authority?

Answer 19

Yes