Myasthenia Gravis

Question 1

what is the general presentation of myasthenia Gravis?

Answer 1

Fatigable muscles (muscle weakness worsening after periods of activity and improves after periods of rest) and norm reflexes + no sensory symp – associated with thymic hyperplasia(and thymomas)

RESTRICTIVE PATTERN OF LUNG DISEASE

Question 2

Define myasthenia Gravis?

Answer 2

autoimmune disease affecting neuromusular junction producing weakness in skeletal muscles

Question 3

define myasthenia gravis?

Answer 3

autoimmune disease affecting the post synpatic membrane at the neuromuscular junction producing weakness in skeletal muscles

Question 4

outlinethe aetiology of myasthenia gravis?

Answer 4

antibodies against nicotinic acetylcholine receptor which interferes with neuromuscular transmission via depletion of post- synaptic receptor sites

Question 5

what is lamberton Eaton syndrome?

Answer 5

paraneoplastic subtype of myasthenia gravis caused by autoantibodies against pre-synaptic calcium channels leading to impairement of acetyl choline release

can be paraneoplastic ( from small cell lung cancer) or autoimmune

Question 6

what are the symptoms and signs of lambert- eaton syndrome

Answer 6

Question 7

what conditions if myasthenia gravis associated with?

Answer 7

associated with other autoimmune conditions ->PERNICIOUS ANAEMIA AND THYMOMA

associated with thymus hyperplasia

Question 8

summarise the epidemiology of myasthenia gravis?

Answer 8

Prevalence: 8-9/100,000

More common in FEMALES under 50

More common in MALES after 50

Question 9

what are the presenting symptoms of myasthenia gravis?

Answer 9

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

order of muscle weakness extraocular -> bulbar-> face-> neck-> limb girdle-> trunk

ocular symptoms

• ptosis
• diplopia

Bulbar symptoms

• facial paresis ( myasthenic snarl)
• dysarthria -disturbed hypernasal speech
• dysphagia-difficulties chewing and swallowing

Proximal limb weakness

• difficult to get out of chairs or climb stairs

Question 10

how is the fatigue from lamberton-eaton syndrome different to myasthenia gravis?

Answer 10

lamberton-eaton syndrome=muscle weakness improves after repeated use

myasthenia gravis= weakness worsens on activity ( fatigue) and improves on rest

Question 12

what is the order of muscle weakness in myasthenia gravis?

Answer 12

extraocular -> bulbar -> face -> neck -> limb girdle-> trunk

Question 13

what are the signs of myasthenia gravis?

Answer 13

May be generalised (affecting many muscle groups)

Eye Signs

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

Ice on Eyes Test

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

Bulbar Signs

• Reading aloud may cause dysarthria or nasal speech – on counting to 50, the voice fades

Limbs

• Test the power of a muscle before and after repeated use of the muscle
• Tendon reflexes are normal

Tensilon Test

Question 14

what is the tensilon test?

Answer 14

administering a very short-acting acetylcholinesterase inhibitor to diagnose myasthenia gravis by demonstrating by a rapid improvement in muscle weakness

Question 15

what are the signs on Lamberton-Eaton syndrome on physical examination?

Answer 15

gait difficulty before eye signs, autonomic involvement (dry eyes, constipation), hyporeflexia and weakness that improves after exercise – depressed tendon reflexes are because less transmitter is released but reflexes may increase after maximum voluntary contractions due to build up of transmitter in the synaptic cleft.

Question 16

what are the investigations for myasthenia Gravis?

Answer 16

CK - exclude myopathies

Serum acetylcholine receptor antibody (positive in 90%)

If seronegative, look for MUSK antibodies (multiple specific tyrosine kinase)

TFTs (it is associated with hyperthyroidism)

Serial PFTs

• MG crisis: low FVC and NIF (negative inspiratory force) - only is SOB in history

Question 17

what are the investigations for lamberton eaton syndrome?

Answer 17

Anti-voltage gated calcium channel antibody (in Lambert-Eaton syndrome)

autoantibodies interfere with the normal influx of pre-synaptic calcium that allows for release of acetylcholin->results in less post-synaptic stimulation.

Repetitive stimulation allows for acetylcholine levels to reach sufficient levels to improve muscle contraction, which explains why patients’ weakness briefly improves with repetitive testing.

Question 18

what investigations should you consider for laberton eaton syndrome?

Answer 18

Nerve Conduction Study

• Repetitive stimulation shows decrements of muscle action potential

EMG

CT Thorax/CXR - visualise thymoma in the mediastinum or lung malignancies – found in 20% of MG pati