NMJ Disorders

Question 1

MC NMJ disorder

Answer 1

Myasthenia Gravis

Question 2

Three types of myasthenia

Answer 2

• generalized
• ocular
• bulbar

Question 3

Age/Sex MC seen in myasthenia

Answer 3

females: teens-30s
males: 50-70
(Bimodal distribution)

Question 4

Three pathophys mechanisms that lead to myasthenia

Answer 4

1) Direct blocking of the nicotinic AchR site
2) Accelerated internalization of the AchR by crosslinking of IgG
3) Complement mediated lysis of the muscle end plate

Question 5

How commonly is thymus involved in myasthenia?

Answer 5

50% have thymic hyperplasia
10-15% have thymoma

(Thymocytes produce the AchR Ab)

Question 6

Classic symptom description for myasthenia:

Answer 6

• fatigable weakness
• diurnal variation (worse at night)

**Normal sensation, reflexes

Question 7

Most common Ab assc with MG

Answer 7

AchR BINDING Ab

1st screening test for myasthenia, may not ALWAYS be present especially in ocular MG

Question 8

Myasthenia Ab that is assc with thymoma

Answer 8

Anti-striated muscle

seen in 75-80% of those with thymoma, also sometimes those without

Question 9

In addition to screening for Ab’s, what other tests are diagnostic for MG:

Answer 9

• repetitive nerve stimulation

- edrophonium/tensilon test

Question 10

How sensitive/specific is tensilon test for MG?

Answer 10

“71-95%” sensitive
not very specific
not reliable in anti-MuSK MG

Question 11

Side effects assc with the tensilon test

Answer 11

bradycardia, hypotension (treat with atropine)

Question 12

What must be done to ensure there is no bias in tensilon testing?

Answer 12

-patient+ docs blind, only nurse may know in which order patient receives placebo vs tensilon

Question 13

MC treatment for symptom reduction in myasthenia

Answer 13

• pyridostigmine (mestinon)

- AchEi

Question 14

Effect of mestinon on end plate potential

Answer 14

increases size and length of end plate potential

Question 15

ADRs assc with mestinon

Answer 15

liquid out of all the places.

diarrhea, runny nose, sweating, vomiting etc

Question 16

Short term therapies to suppress immune system in MG?

Answer 16

• plasma exchange

- IVIG

Question 17

Long term therapies to suppress immune system in MG?

Answer 17

• thymectomy
• corticosteroids
• azathioprine/ mycophenolate

Question 18

Why must plasma exchange be done every OTHER day for 3-6 days as opposed to EVERY day?

Answer 18

-It depletes clotting factors

Question 19

When are Plasma exchange and IVIG used for MG

Answer 19

-exacerbations, resistant cases

Question 20

What patients should have prophylactic thymectomy in MG?

Answer 20

-Most patients under 50

Question 21

Lambert Eaton:

• MC sex
• paraneoplastic of what cx?
• how commonly is LEMS paraneoplastic?

Answer 21

• males=females
• small cell, half of LEMS patients have small cell, 3% of small cell patients have LEMS

**IF YOU DIAGNOSE LEMS YOU HAVE TO SCREEN FOR SMALL CELL!!!!!!!

Question 22

Non small cell LEMS is most commonly assc with?

Answer 22

-younger females with other autoimmune disease

Question 23

What antibody is responsible for lambert eaton?

Answer 23

-IgG antibody against voltage gated calcium channel

Ca is responsible for the release of Ach at NMJ

Question 24

How does LEMS effect the motor end plate potential?

Answer 24

-decreased –> failed transmission –> low CMAP

Question 25

Typical initial presentation of LEMS

Answer 25

• proximal leg/arm weakness that improves w/ exercise
• MILD CN sx
• dry eyes/mouth, metallic taste
• absent reflexes (UNLIKE MG)
• normal sensation

Question 26

Subtle signs of LEMS (2)

Answer 26

• weakness if given CCB for HTN

- prolonged paralysis following intubation

Question 27

How does repetitive stimulation testing vary in LEMS vs MG?

Answer 27

• increased end plate potential over time in LEMS

- decreased EPP over time in MG

Question 28

Three possible MG antibodies

Answer 28

• antiMUSK
• antiAchR
• anti striated muscle