Neuromuscular Junction Disorders Flashcards
What is post activation exhaustion
Decrease in CMAP amplitude seen 5 minutes after isometric contraction
Myasthenia gravis vs lambert eaton syndrome: quantal content vs quantal response
MG: normal quantal content, but decrease quantal response
LES: decreased quantal content, normal quantal response
Which NMJ has normal CMAP and which has abnormal CMAP
MG has normal CMAP. Botulism and LES have abnormal CMAP.
Treatment of MG
Thymectomy, anticholinesterase (pyridostigmine), steroids, plasmapharesis, IVIg
Treatment of botulism
Antitoxin
High rate repetitive simulation Findings seen in NMJ disorders
MG -decrement and partially repaired
LES - 200-300% increment
Botulism - mild increment
Which NMJ is better with exercise and which is worse with exercise
MG is worse with exercise and LES is better with exercise
Which limbs are affected first in LES
Lower limbs (quadriceps)
What is post activation facilitation
Isometric contraction increases CMAP amplitude because of improvement in neuromuscular transmission because of bombardment of ACh
Etiology of MG
Autoimmune response against postsynaptic muscle specific tyrosine kinase ACh receptors
Which NMJ disorder has proximal fatigue and weakness
MG and LES
What is the most common muscle weakness seen in MG
Ocular weakness (ptosis)
Diagnostic test for MG
Edrophonium (tensilon) test - improvement begins in 1 minute. Edrophonium is a short acting cholinesterase inhibitor
Which NMJ disorder is associated with thymus disorder/thymoma
MG
Prior to doing a repetitive nerve stimulation study, what changes must be done to meds
Stop cholinesterase inhibitors 12 hours before study
Which NMJ includes facial or bulbar symptoms, and what are they?
MG and botulism - ptosis, diplopia, dysphagia, dysarthria
Most sensitive test for NMJ disorder
Single fiber EMG
What kind of cancer is LES associated with
Small cell carcinoma
MG vs LES Miniature endplate potential and frequency of potential
MG = reduced MEPP, normal frequency LES = normal MEPP, reduced frequency
What causes jitter
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Finding on repetitive nerve stimulation study for NMJ disorder
> 10% decrement in amplitude between first and fifth waveform
SNAP findings of NMJ disorders
Normal
Treatment of LES
Steroids, plasmapheresis, guanidine (increases ACh), IVIg
CMAP finding of NMJ disorder
Normal or reduced amplitude
Etiology of botulism
Clostridium botulinum toxin blocks presynaptic release of Ach
Etiology of LES
Autoimmune response against voltage gated calcium channels of presynaptic membrane decreasing calcium entry into cell which decreases release of Ach
Which NMJ disorder has normal and abnormal MSR
Normal = MG Abnormal = LES and botulism
MG vs LES vs Botulism: postsynaptic vs presynaptic
MG = postsynaptic problem LES = presynaptic problem Botulism = presynaptic problem