Myasthenia Gravis

Question 1

which type of autoimmune disorder

Answer 1

II - antibodies against AChR form immune complexes and are deposited at post synaptic memrbane

Question 2

most common age and sex

Answer 2

2 incidence peaks in childbearing females and older males

twice as common in women

Question 3

who does MuSK predominantly effect

Answer 3

women

Question 4

which muscles does it effect, and which group lof muscles can the disease solely present in

Answer 4

proximal limb muscles, bulbar and ocular - can have purely ocular disease

Question 5

what is the main underlying pathology

Answer 5

antibodies present in the NMJ:

• attack the nicotnic ACh receptor - inconsistent generation of muscle fibre AP - skeletal muscle weakness
• produce inflammatory cascade - damage and destroy post synpatic membrane

Question 6

what is seronegative MG

Answer 6

those who don have AChR antibodies, often have muscle specific tyrosine kinase antibodies

Question 7

does seronegative MG present differently

Answer 7

Likely to have more mild disease, with weakness in ocular, bulbar, facial and neck muscles.

Question 8

what is the role of muscle specific tyrosine kinase, which Ab are directed against in MuSK

Answer 8

helps to anchor AChReceptors at post synaptic folds

Question 9

which paraneoplastic sydnrome is MG associated wtih

Answer 9

thymoma

Question 10

which thymus problem is MG usually associated with

Answer 10

thymic follicular hyperplasia (70%)

Question 11

what is the link between thymus and MG

Answer 11

unsure, associated with thymic follicular hyperplasia and thymoma in 70% and 10% cases

more so in young people

thymectomy is seen to be of benefit even in the absence of thymus abnormality

Question 12

what are the classical features of the muscle weakness

Answer 12

• worsens on repetitive movement
• worsens throughout day
• eg may be fine in morning

Question 13

is muscle pain present

Answer 13

no

Question 14

which muscles are particularly affected?

Answer 14

extraocular muscles

• ptosis
• diploplia

Question 15

are pupillary defects seen

Answer 15

no, only extraocular muscles

Question 16

what test can be done that will improve ptosis in most patients

Answer 16

ice test - cool ≥2 mins with ice pack

Question 17

if you pull on the patients upper lid what might happen to the contralateral lid

Answer 17

induce ptosis

Question 18

what are symptoms of muscles in the throat and neck beingaffected

Answer 18

• dysphagia
• dysarthria
• facial paresis

Question 19

how does involvement of the chewing and swallowing muscles present problems

Answer 19

patient may not be able to finish meal

choking

Question 20

which limb muscles are often involved

Answer 20

proximal limb weakness

Question 21

how does proximal limb weakness tend to present

Answer 21

difficulty getting out of chair or climbing stairs

Question 22

is there muscle wasting?

Answer 22

no

Question 23

is proximal limb weakness a early or late onset feature

Answer 23

late

Question 24

weakness of which muscle in particular is a distinctive clinical sign as there are not many other diseases that cause this (not eyes)

Answer 24

neck flexion weakness, eg head feels heavy

Question 25

respiratory muscle involvement

Answer 25

can cause SOB

Question 26

MG crisis

Answer 26

caused by respiratory muscle weakness - if the SOB is bad enough that the patient requires mechanical ventilation it is MG crisis

Question 27

what tests should be performed to investigate respiratory muscle function if the patient presents with SOB, or there is a suspected MG crisis

Answer 27

pulmonary function tests - FVC

Question 28

investigations indicated for MG

Answer 28

serum analysis of antibodies - 80-90% of patients have AChR antibodies, 70% of AChR seronegative pt have MuSK antibodies

Question 29

do patients presenting withb ocular MG have more or less likelihood of having AChR antibodies ?

Answer 29

less, around 50%

Question 30

what complications can impaired swallowing lead to

Answer 30

aspiration and 2y pneumonia

Question 31

first line treatment

Answer 31

pyridostigmine - a cholinesterase inhibitor

Question 32

how is pyridostimine adminstered, and when

Answer 32

PO or IV 30min prior to eating, a sustained release form is available for night time dosing

Question 33

2nd line treatment for those who fail on pyridostigmine

Answer 33

corticosteroids eg prednisolone

Question 34

what is the first line treatment for patients wtih ocular MG

Answer 34

corticosteroids

Question 35

when is imunosuppression considered

Answer 35

when pt are on high dose of steroids, particualrly if they have co morbidities that complicate this eg diabetes, hypertension, glaucoma, obesity

Question 36

which surgical procedure is shown to be of benefit in all pt

Answer 36

thymectomy - even if there is no abnormality

Question 37

why is thymectomy of benefit, and is it good for both types of antibody related disease?

Answer 37

* thymoma has possibility of malingancy * more effective in positive AChR antibodies than anti MuSK antibodies

Question 38

management of acute disease

Answer 38

plasma exchange or IV immunoglobulin

Question 39

mortality?

Answer 39

low, tends to occur from resp failure or aspiration pneumonia

Question 40

which organisms is typically found in aspiration pneumonia

Answer 40

Klebsiella - red jelly sputum

Question 41

when in the disease course does MG crisis usually occur

Answer 41

within the first 2 years of diagnosis

Question 42

name 4 drug/classes that must be avoided

Answer 42

aminoglycosides, steroids, ciprofloxacin, beta blockers

Question 43

aminoglycosides and MG

Answer 43

ipair neuromuscular transmission and can cause clinically significant muscle weakness - resp depression - crisis

Question 44

steroids and MG - dangers

Answer 44

pt will be stabilized on a maintenance dose of prednisolone (±steroid sparing agent) , sudden increase/decrease can directly inhibit NM function - worsen status - crisis