Sachen: Disorders of the Neuromuscular Junction (NMJ)

Question 1

Which 2 HLA haplotypes are seen with high frequency in Myasthenia Gravis?

Answer 1

HLA-B8 and DR3

Question 2

What is tx for Myasthenia Gravis pt’s in crisis or prior to undergoing surgery to avoid crisis?

Answer 2

IVIg / plasma exchange

Question 3

Which drug can cause a disorder identical to Myasthenia Gravis?

Answer 3

D-penicillamine

Question 4

Which antibodies are seen in about 40% of Myasthenia Gravis pt’s with no detectable anti-AChR Ab’s?

How do we tx these pt’s?

Answer 4

MUSK (muscle specific tyrosine kinase) Ab’s

Tx: PLEX/IVIg/rituximab is best, poor resp to AchE/thymectomy

Question 5

What are the 3 general characteristics of Myasthenia Gravis?

Answer 5

1. Fluctuating weakness
2. Distribution of weakness: ocular ms, dysarthria, dysphagia, resp insuff
3. Clinical resp to AchE drugs

Question 6

Out of the 4 forms of myasthenia gravis, which is the most common?

Answer 6

Question 7

What is some lab data assc with MG?

Answer 7

• AchR ab = 55% of ocular MG, 80% of general
• MUSK ab
• LRP-4 ab
• EMG findings = dec response w repeated stimulation, inc jitter on single fiber
• Tests = fatigable weakness, ice bag, Cogan’s sign

Question 8

Describe the Tensilon test. What are some complications?

Answer 8

Tensilon = edrophonium test, pos in 90% of pt’s

• AE: bradycardia, ventricular arrythmia
• Keep atropine on hand

Question 9

What surgery may be helpful to Rx MG, but probably if it is purely ocular?

Answer 9

Thymectomy

Question 10

Which abx is known for exacerbating MG?

Answer 10

Aminoglycosides

Question 11

Define MG crisis versus cholinergic crisis

What are the s/s? What meds would we give?

Answer 11

MG Crisis = disease itself rapidly worsens

• infection or drug may trigger
• S/s: aspiration, weakness, resp failure
• STOP AchE meds, use PLEX/IVIg/steroids

Cholinergic crisis = rapid inc in weakness from excess AchE meds

• S/s: n/v, sweating, salivating, diarrhea, bradycardia
• HALLMARK: miosis and fasciculations

Question 12

What condition do we assc with Lambert-Eaton?

Answer 12

Small cell lung cx

Question 13

How do we treat Lambert-Eaton?

Answer 13

• R/O cancer
• Mestinon (AchE inh) may improve weakness
• Amifampridine
• 3-4 Diaminopyridine
• Guanidine hydrochloride: cause bone marrow suppression
• IVIg

Question 14

What are the s/s of Botulism? What is the Rx?

Answer 14

Symptoms

• dry, sore mouth, blurred vision, diplopia, n/v
• hypohydrosis, external ophthalmoplegia
• facial, mouth, and resp paralysis

Treatment

• Antitoxin: horse serum
• Guanidine hydrochoride

Question 15

What AE should we assc w Guanidine Hydrochloride?

Answer 15

Bone marrow suppression

(Treats LE and Botulism)

Question 16

What are some s/s of organophosphates poisoning (Sarin and VX gas)?

Answer 16

Miosis, inc secretions, bronchospasm, n/v/d

Inc HR and BP

Weakness and fasciculations, seizures

LOC, death by resp failure

Question 17

What are 3 tx for organophosphate poisoning?

Answer 17

1. Atropine
2. Pralidoxime
3. Benzo: seizures only respond to this