NMJ Disorders (Hon)

Question 1

Myasthenia Gravis pathophysiology

Answer 1

defect in neuromuscular transmission by antibodies attacking the nicotinic acetylcholine receptors on the post synaptic membrane (muscle membrane)

Question 2

Myasthenia Gravis is associated with what hereditary subset?

Answer 2

HLA-B8 and HLA-DR3

Question 3

Myasthenia Gravis is often seen with what other disorders?

Answer 3

autoimmune (SLE, RA, thyroid disorders, DM1, crohns, etc)

Question 4

Incidence of Myasthenia Gravis in men and women?

Answer 4

more common in younger women and older men

Question 5

What are the 3 general characteristics of Myasthenia Gravis?

Answer 5

1. excessive fatiguability (fluctuating weakness)
2. Distribution of weakness (ocular muscles -ptosis/diplopia)
3. Clinical response to cholinergic drugs

Question 6

EMG in a Myasthenia Gravis patient?

Answer 6

decremental response on repetitive stimulation

Question 7

What type of antibodies would you suspect to find in a Myasthenia Gravis patient?

Answer 7

acetylcholine receptor antibodies (anti-AChR abs)

Question 8

The ice bag test is helpful for diagnosis of which NMJ pathology?

Answer 8

Myasthenia Gravis; apply ice to ptotic lids for 2 mins and if 2 mm improvement in ptosis then it is considered a positive test

Question 9

Answer 9

A is a normal EMG with repetition stimulation and B is showing an EMG with decreased response on repetition stimulation as seen in Myasthenia Gravis.

Question 10

Treatment for Myasthenia Gravis?

Answer 10

an anticholinergic (Mestinon), steroids (prednisone), can use plasma exchange/IVIg for patients in a crisis and a thymectomy has been found to be helpful

Question 11

Why is it important to thoroughly consider treatment for patients with Myasthenia Gravis?

Answer 11

because there are LOTS of drugs that make the disease worse!

Question 12

Myasthenia crisis

Answer 12

rapid deterioration of Myasthenia Gravis; may occur spontaneous or after infection or drug use; patient will experience aspiration, diffuse weakness, and possible respiration

MAKE SURE TO STOP ANTICHOLINERGIC MEDS!!

Question 13

How should you alter the treatment plan for someone experiencing a Myasthenia crisis?

Answer 13

STOP ANTICHOLINERGIC MEDS!! use PLEX or IVIg

Question 14

What is a big clue in clinical presentation that a patient is experiencing a cholinergic crisis and not a Myasthenia crisis?

Answer 14

presence of miosis and/or fasciculations

Question 15

Cholinergic crisis

Answer 15

rapid increase in weakness from excess anti cholinesterase meds (more acetylcholine in NMJ plate); will see n/v, increased sweating/saliva, bradycardia and look for miosis and/or fasciculations

Question 16

Seronegative Myasthenia Gravis

Answer 16

none of the typical MG antibodies are found in serum; no anti-AChR abs; check for MuSK antibodies for MuSK syndrome

Question 17

What are the 3 general types of MuSK Syndrome?

Answer 17

1. oculopharyngeal weakness
2. neck, shoulder and respiratory weakness
3. indistinguishable from antibody positive MG

Question 18

What is the treatment for MuSK syndrome?

Answer 18

Poor response to anti cholinesterase medications and thymectomy; treat with PLEX, IVIg and riuximab

Question 19

MuSK syndrome

Answer 19

similar to Myasthenia Gravis but there are no MG antibodies found in serum; no anti-AChR abs; positive for MuSK antibodies

Question 20

Double seronegative MG

Answer 20

none of the typical MG antibodies are found in serum or the MuSK antibodies; check for anti-LRP4 antibodies; symptoms milder and there is frequent ocular involvement

Question 21

Lambert-Eaton Myasthenia Syndrome (LEMS) pathophysiology

Answer 21

autoimmune attack against voltage-gated calcium channels (VGCC’s) on the presynaptic terminal; affects Ach release at the NMJ

Question 22

Lambert-Eaton Myasthenia Syndrome (LEMS) is often associated with what?

Answer 22

malignancy; check for small cell carcinoma of the lung

Question 23

What is the typical clinical presentation of a patient with Lambert-Eaton Myasthenia Syndrome (LEMS)?

Answer 23

proximal weakness, areflexia, dry mouth, strength may improve after exercise

Question 24

What antibodies are you looking for in someone with Lambert-Eaton Myasthenia Syndrome (LEMS)?

Answer 24

voltage gated calcium channel antibodies (VGCC’s)

Question 25

What is the typical EMG finding in a patient with Lambert-Eaton Myasthenia Syndrome (LEMS)?

Answer 25

incremental response on fast repetitive stimulation (often greater than 100%)

Question 26

Answer 26

incremental response on fast repetitive stimulation (often greater than 100%) as seen in Lambert-Eaton Myasthenia Syndrome (LEMS)

Question 27

What should you look for in a patient with Lambert-Eaton Myasthenia Syndrome (LEMS)?

Answer 27

look for and treat malignancy; typically small cell carcinoma of the lung

Question 28

Treatment for a patient with Lambert-Eaton Myasthenia Syndrome (LEMS)?

Answer 28

first look for and treat malignancy
treat with acetylcholinesterase inhibitors, immunosuppression and IVIg

Question 29

Botulism

Answer 29

toxin that blocks the presynaptic mechanisms for the release of ACh; presents with dry, sore mouth and throat, blurred vision, diplopia and n/v; watch for limb and respiratory paralysis; treat in ICU with respiratory support

Question 30

Why is it cautioned against treating with the antitoxin in botulism poisoning?

Answer 30

the antitoxin is a horse serum product and can cause serum sickness or anaphylaxis and make the condition much worse; if can monitor patient and provide respiratory support until toxin is eliminated then patient will typically recover