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BR 3rd Ed > Ch 5 - EDX: NMJ Disorders > Flashcards

Ch 5 - EDX: NMJ Disorders Flashcards

1
Q

What is Myasthenia gravis (MG)?

A

Disorder of NT d/t an AI response against Muscle specific Tyrosine kinase (MuSK) postsynaptic ACh receptors leading to dec quantal response and MEPP

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2
Q

What is Lambert-Eaton myasthenic syndrome (LEMS)?

A

Disorder of NT d/t AI response against voltage gated Ca++ channels on presynaptic membrane resulting in dec Ach leaving the presynaptic cleft

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3
Q

What can be added to typical EDX studies to evaluate NMJ?

A

Repetitive nerve
stimulations (RNSs)
Single-fiber EMG (SFEMG)

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4
Q

What is seen on CMAP testing in Lambert-Eaton myasthenic syndrome (LEMS)?

A

Low CMAP, then 10 sec max voluntary contraction leads to inc amp >100% compared to premax contraction

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5
Q

What is associated with MG?

A

Thymic disorders

Thymic tumor

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6
Q

What is the onset of MG?

A 
Bimodial
1st peak: 20-30 yo
Female>male
2nd peak: 60-80 yo
Female=male
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7
Q

What is the clinical presentation of MG?

A

Ocular weakness MC
Proximal fatigue/weakness
Exacerbated by exercise, heat, end of day
Improved with rest

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8
Q

How can MG be diagnosed?

A

Edrophonium (Tensilon) Test: 2-mg dose followed by a 8-mg dose, improvement begins in 1 minute

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9
Q

What is LEMS associated with?

A

Small cell (oat cell) carcinoma of the lung (50% are paraneoplastic)

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10
Q

What is the onset of LEMS?

A 
Bimodal distribution 
1st Peak: 40 years
Female > male 
2nd Peak: 60 years 
Male > female
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11
Q

What is he clinical presentation of LEMS?

A 
Proximal fatigue/weakness with rest
Mainly LE (quadriceps)
Viselike grip
Rare face/neck sx
Autonomic sx (dry mouth, ED, constipation)
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12
Q

What is Botulism?

A

NT d/o caused by Clostridium botulinum toxins blocking presynaptic exocytosis of ACh from the nerve terminal

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13
Q

What is the onset of Botulism?

A

Begins 2 to 7 days after ingestion

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14
Q

What is the clinical presentation of Botulism?

A 
Dec DTRs
Bulbar sx first
GI sx: N/V/D
Wide spread paralysis/flaccidity
Respiratory/cardiac dysfxn
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15
Q

What is seen on muscle bx in MG?

A

Simplification of the postsymptomatic membrane with loss of junctional folds and receptors

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16
Q

What is seen on labs in MG?

A

Anti-Ach receptor Abs

Anti-MuSK Abs

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17
Q

What is seen on NCS in MG?

A

Normal SNAP and CMAP

>10% decrement on low rate rep. stim

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18
Q

What is seen on EMG in MG?

A

Unstable MUAP, drop-off occurs with sustained contraction

19
Q

What are treatments for MG?

A

Thymectomy Anticholinesterase drugs: Mestinon (Pyridostigmine)
Corticosteroids Immunosuppressive agents
Plasmapheresis
1/3 improve spontaneously
IV Immunoglobulin

20
Q

What is seen on muscle bx in LEMS?

A

Overdevelopment of neuromuscular junction

21
Q

What is seen in labs in LEMS?

A

Abs against voltage-gated Ca+ channels

22
Q

What is seen on NCS in LEMS?

A

Normal SNAP
Low CMAP
>10% decrement on low rate rep. stim

23
Q

What is seen on EMG in LEMS?

A

Unstable MUAP, drop-off occurs with sustained contraction

24
Q

What are treatments for LEMS?

A 
Treat malignancy Corticosteroids 
Immunosuppressive agents Plasmapheresis
Guanidine
3,4-diaminopyridine 
IV Immunoglobulin
25
Q

What are guanidine MOA and SE?

A

Inc ACh quanta

SE: GI, bone marrow suppression, renal tubular necrosis

26
Q

What is seen on EDX in botulism?

A

SNAP: Normal
CMAP: ABN Amp
>10% decrement on rep. stim. study
Unstable MUAP on EMG

27
Q

What are treatments for Botulism?

A

Trivalent ABE antitoxin in 1st24hours

Supportive respiratory care

28
Q

How does neurologic recover occur in Botulism?

A

Collateral sprouting

29
Q

Describe repetitive nerve stimulation

A

Repeated supramaximal stim over motor nerve in clinically weak muscles

30
Q

What is the recommended order for muscle evaluation in repetitive nerve stimulation?

A

1st: ADM or ABP
2nd: Deltoid
3rd: Trapezius
4th: Obicularis oculi

31
Q

What is Low Rate Repetitive stim (LRRS)?

A

Repetitive stim test is performed at a rate of 2 to 3 Hz

32
Q

What amplitude changes are seen with MG, LEMS, and Botulism in Low Rate Repetitive stim (LRRS)?

A

> 10% decrement

33
Q

What is High Rate Repetitive stim (HRRS)?

A

Repetitive stim test is performed at a rate of 10 to 50 Hz

34
Q

What does High Rate Repetitive stim (HRRS) cause?

A

Accumulation of Ca++ in the cell, which assists ACh release and repairs the waveforms

35
Q

What amplitude changes are seen with MG, LEMS, and Botulism in High Rate Repetitive stim (HRRS)?

A

MG: decrement demonstrated and partially repaired
LEMS: 200-30% increment
Botulism: mild increment >40%

36
Q

What is Pseudofacilitiation?

A

Normal rxn and demonstrates a progressive inc in CMAP Amp with HRRS or voluntary muscle contraction

37
Q

What is single fiber EMG?

A

Study that monitors the parameters of single muscle fiber AP

38
Q

What is single fiber EMG useful for?

A

If repetitive stimulation of at least 3 muscles is normal and an ABN diagnosis is
still suspected

39
Q

What is fiber density (FD)?

A

of single fibers belonging to the same motor unit within the recording radius of the electrode

40
Q

What is a normal FD?

A

1.5 is normal

>1.5 represents a denervation and reinnervation process

41
Q

What is jitter?

A

Variation b/w interpotenital discharges of 2 muscles from the same motor unit during a voluntary contraction

42
Q

What can increase jitter?

A

NMJ disease and reinnervation through collateral sprouting

43
Q

What is blocking?

A

ABN occurs when single fiber muscle AP fails to apear when jitter >100 usec

44
Q

When does blocking typically resolve?

A

1-3 months after reinnervation complete

BR 3rd Ed (92 decks)

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