4: Disorders of NMJ - Kruse

Question 1

NMJ physiology

Answer 1

• Neuron depolarizes
• Voltage Gated Calcium channel allows influx of ions
• Ach filled vesicles merge with the neuron membrane
• Ach is released into the synaptic gap
• Ach is released into the synaptic gap
• Ach crosses the gap and binds to Nicotinic receptors triggering muscle depolarization
• If serial depolarizations occur a sustained muscle contraction can occur
• Acetylcholinesterase breaks down Ach allowing the receptor to turn off

Question 2

in alcohol rleated transaminitis, why does AST elevate more than ALT?

Answer 2

ALT is more specific for the liver, but AST is more muscle related (rhabdomyolysis)

Question 3

gold standard imaging for patient with vague neurologic and musculoskeletal symptoms

Answer 3

MRI

Question 4

*****location of breakdown = presynaptic. give examples

Answer 4

botulism

lambert- eaton syndrome

Question 5

*****location of breakdown = synaptic. Give examples.

Answer 5

acetylcholinesterase inhibitors

Question 6

***** location of breakdown = postsynaptic. Give examples.

Answer 6

myasthenia gravis

snake venom

Question 7

*** describe myasthenia gravis

Answer 7

anti-acetylcholine receptor antibodies attack the postynaptic m. membrane decreasing the number of receptors and blocking the remaining receptors

Question 8

*** describe lambert eaton syndrome

Answer 8

anti-calcium channel antibodies attack the presynaptic neuron membrane and prevent acetylcholine release

Question 9

*** describe botulism

Answer 9

botulinum toxin acts at the presynaptic neuron membrane and prevent release of acetylcholine

• infants honey, canned food, supportive treatment

Question 10

ptosis that improves with an ice pack =

Answer 10

myasthenia gravis

also see blurred vision, ptosis, bulbar symptoms, weakness

key terms: fatigability and fluctuation

Question 11

cause of 85% of myasthenia gravis

Answer 11

anti-acetylcholine receptor antibodies

40% of remaining cases have anti-MuSK antibodies which also disrupt the muscular endplate

Question 12

when do you need to initiate mechanical ventilation for neuromuscular disease?

Answer 12

• negative inspiratory force less negative than -30 cm H20 (ex: -10)

foced vital capacity less than 15-20 ml/kg

significant hypoxemia

patient is in distress*

inability to protect the airway

Question 13

person with muscular weakness gets stronger with exercise

Answer 13

lambert-eaton

lambert-eaton will also show immune precipitation of VGCC antibodies

myasthenia gravis will get weaker

Question 14

***cancer screening for lambert eaton syndrom

Answer 14

image them until they glow

patient has cancer until proven otherwise

if you don’t find cancer on the first pass, repeat imaging q3-6 mo for 2yr

typically a lung cancer