Sachen: Disorders of the Neuromuscular Junction

Question 1

Myasthenia gravis

Answer 1

-caused by a deect o fNM transmission due to an antibody-mediated atack upon nAChR on muscle membrane

Question 2

eiotlogy of MG

Answer 2

• unknown how antiboies arise
• most cases are sporadic, but high frequency of HLA haplotypes B8 and DR3
• often seen with other AI diseases
• younger women

Question 3

sx of MG

Answer 3

• Three things
  1. ) fluctuating weakness
  2. ) distribution of weakness: Ocular muscles
  3. ) clinical response to cholinergic drugs

Question 4

dx of MG

Answer 4

• ACHr ab’s
• MUSK ab’s
• EMG findings: decremental response on repetitive stimulation… increased jitter on single fiber EMG
• Tensilon “edrophonium) test is + .. watch otu for bradycardia

Question 5

what happens with repeated stimulation in MG?

Answer 5

-gets weaker after first response

Question 6

What is tensilon

Answer 6

• AChE inhibitor
• so it makes the sx better in MG
• don’t do this without a monitor or something because of heart probs

Question 7

MG tx

Answer 7

• AchE inhibitors
• prednisone
• immunosuppressive agents
• plasma exchange
• thymectomy, probably helpful, but optional

Question 8

what are some drugs that can unmask MG

Answer 8

• aminogycosides

- NM blockers (succinlylcholine)

Question 9

Lambert Eaton myasthenic syndrome (LEMS)

Answer 9

• AI attack against calcium channels on the presynaptic nerve terminal
• presynaptic abnormality of Ach release at the neuromuscular junction leads to weakness
• often associated with cancer

Question 10

clinical presentation with LEMS

Answer 10

• prox weakness, loss of dtr, dry mouth

- strength may improve after exercise****

Question 11

lab data for LEMS

Answer 11

• ab’s against VGCC’s
• EMG: low amp motor responses that facilitate after a brief period of exercise
• incremental response onfast repetitive stimulation

Question 12

tx of LEMS

Answer 12

• first look for and tx malignancy
• Ach inhibitors
• 3-4 diaminopyridine
• Guanidine hydrochloride
• immunosuppression
• IvIG

Question 13

Botulism

Answer 13

-toxin blocks presynaptic mechanisms for release of ach

Question 14

presentation of botulism

Answer 14

• dry, soremouth and throat, blurred vision, diplopia, nausea vomiting
• can see hypohydrosis, total external ophthalmoplegia, facia, oropharyngea, limb, and resp paralysis

Question 15

Tx of botulism

Answer 15

• ICU monitoring with resp support and general medical care
• Antitoxin
• Guanidine hydrochloride (side effect of bone marrow suppression)

Question 16

What do nerve gases do?

Answer 16

• inhibit ACHe at NMJ to cause end organ overstimulation

- death by resp failure

Question 17

do you get fasciculations in MG or LEMS?

Answer 17

• no
• but you do for cholinergic excess
• i think that pupil things are specific to nerve gases as well

Question 18

tx of nerve gases

Answer 18

• decontamination: remove clothes, clean skin with water and sodium hypochlorite
• resp support
• antidotes: atropine, pralidoxime
• Seizures: they only respond to benzodiazepines