Ch 5 - EDX: NMJ Disorders Flashcards by Carmel@Brainscape AdminPro

What is Myasthenia gravis (MG)?

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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What is Lambert-Eaton myasthenic syndrome (LEMS)?

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

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

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

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

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What is associated with MG?

Thymic disorders

Thymic tumor

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What is the onset of MG?

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

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What is the clinical presentation of MG?

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

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How can MG be diagnosed?

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

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What is LEMS associated with?

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

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What is the onset of LEMS?

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

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What is the clinical presentation of LEMS?

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

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What is Botulism?

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

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What is the onset of Botulism?

Begins 2 to 7 days after ingestion

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What is the clinical presentation of Botulism?

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

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What is seen on muscle bx in MG?

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

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What is seen on labs in MG?

Anti-Ach receptor Abs

Anti-MuSK Abs

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What is seen on NCS in MG?

Normal SNAP and CMAP

>10% decrement on low rate rep. stim

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What is seen on EMG in MG?

Unstable MUAP, drop-off occurs with sustained contraction

What are treatments for MG?

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

What is seen on muscle bx in LEMS?

Overdevelopment of neuromuscular junction

What is seen in labs in LEMS?

Abs against voltage-gated Ca+ channels

What is seen on NCS in LEMS?

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

What is seen on EMG in LEMS?

Unstable MUAP, drop-off occurs with sustained contraction

What are treatments for LEMS?

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

What are guanidine MOA and SE?

Inc ACh quanta | SE: GI, bone marrow suppression, renal tubular necrosis

What is seen on EDX in botulism?

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

What are treatments for Botulism?

Trivalent ABE antitoxin in 1st 24 hours | Supportive respiratory care

How does neurologic recovery occur in Botulism?

Collateral sprouting

Describe repetitive nerve stimulation

Repeated supramaximal stim over motor nerve in clinically weak muscles

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

1st: ADM or APB 2nd: Deltoid 3rd: Trapezius 4th: Orbicularis oculi

What is Low Rate Repetitive stim (LRRS)?

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

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

>10% decrement

What is High Rate Repetitive stim (HRRS)?

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

What does High Rate Repetitive stim (HRRS) cause?

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

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

MG: decrement demonstrated and partially repaired LEMS: 200-300% increment Botulism: mild increment >40%

What is Pseudofacilitiation?

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

What is single fiber EMG?

Study that monitors the parameters of single muscle fiber AP

What is single fiber EMG useful for?

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

What is fiber density (FD)?

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

What is a normal FD?

1.5 is normal | >1.5 represents a denervation and reinnervation process

What is jitter?

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

What can increase jitter?

NMJ disease and reinnervation through collateral sprouting

What is blocking?

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

When does blocking typically resolve?

1-3 months after reinnervation complete