Myasthenia Gravis

Question 1

Define Myasthenia Gravis?

Answer 1

An autoimmune disease affecting the neuromuscular junction producing weakness in skeletal muscles

Question 2

What is the aetiology of Myasthenia Gravis?

Answer 2

Impairment of neuromuscular junction transimission

Question 3

What is Myasthenia Gravis most commonly due to?

Answer 3

Autoantibodies against the nicotinic acetylcholine receptor

Question 4

What is Lambert-Eaton Syndrome?

Answer 4

Pareneoplastic subtype of myasthenia gravis caused by autoantibodies against pre-synaptic calcium channels, leading to impairment of acetylcholine release

Question 5

What is an example of another autoimmune condition that Myasthenia Gravis is associated with?

Answer 5

Pernicious Anaemia

Question 6

What is the epidemiology of Myasthenia Gravis?

Answer 6

Prevalence: 8-9/100,000
More common in FEMALES at younger ages
Equal gender distribution in middle agee

Question 7

What is the general presenting symptom of Myasthenia Gravis?

Answer 7

Muscle weakness that worsens with repetitive use or towards the end of the day

Question 8

What happens with muscle weakness in Lambert-Eaton Syndrome?

Answer 8

Improves after repeated use

Question 9

What are the Ocular Symptoms of Myasthenia Gravis?

Answer 9

Drooping eyelids

Diplopia

Question 10

What is the Bulbar symptoms of Myasthenia Gravis?

Answer 10

Facial weakness (myasthenic snarl)
Disturbed hypernasal speech
Difficulty smiling, chewing or swallowing

Question 11

What are the signs of Myasthenia Gravis?

Answer 11

May be generalised (affecting many muscle groups)
May be bulbar (affecting the bublar muscles)
May be ocular

Question 12

What does the term bulbar mean?

Answer 12

Relating to the medulla oblongata (cranial nerves 9,10, 11 and 12 have their nuclei in the medulla)

Question 13

What are the Eye signs of Myasthenia Gravis?

Answer 13

Ptosis
Complex ophthalmoplegia
Check for ocular fatigue by asking the patient to sustain and upward gaze for 1 min and watch the progressive ptosis that develops

Question 14

What is the Ice on Eyes Test for Myasthenia Gravis?

Answer 14

Placing ice packs on closed eyelids for 2 mins can improve neuromuscular transmission and reduce ptosis

Question 15

What are the Bulbar signs of Myasthenia Gravis?

Answer 15

Reading aloud may cause dysarthria or nasal speech

Question 16

What are the signs in the limbs of Myasthenia Gravis?

Answer 16

Test the power of a muscle before and after repeated use of the muscle

Question 17

What investigations do we do for Myasthenia Gravis?

Answer 17

Bloods 
Tensilon Test 
Nerve Conduction Study 
EMG 
CT Thorax/CXR

Question 18

What bloods do we do for Myasthenia Gravis?

Answer 18

CK
Serum acetylcholine receptor antibody
TFYs
Anti-voltage gated calcium channel antibody

Question 19

Why do we do CK bloods for Myasthenia Gravis?

Answer 19

Exclude myopathy

Question 20

Why do we do Serum Acetylcholine Receptor Antibody for Myasthenia Gravis?

Answer 20

Positive in 80%

Question 21

Why do we do TFTs for Myasthenia Gravis?

Answer 21

Myasthenia Gravis is associated with hyperthyroidism

Question 22

Why do we do look for Anti-Voltage gated calcium channel antibodies for Myasthenia Gravis?

Answer 22

They are found in Lambert-Eaton Syndrome

Question 23

What is the Tensilon Test?

Answer 23

Short-acting anti-cholinesterase (edrophonium bromide) increases ACh levels and causes a rapid and transient improvement in clinical features

Question 24

Why do we normally avoid the Tensilon Test for Myasthenia Gravis?

Answer 24

Risk of bradycardia

Question 25

What do we see in Nerve Conduction Study for Myasthenia Gravis?

Answer 25

Repetitive stimulation shows decrements of muscle action potentials

Question 26

Why do we do CT Thorax/CXR for Myasthenia Gravis?

Answer 26

Visualise thymoma in the mediastinum or lung malignancies