Clinical Approach to Disorders of the NMJ Flashcards
What are the most common and most important Pre-synaptic disorder of the NMJ
Lambert-Eaton Myasthenic Syndrome
Botulism
What is the most important Post-synaptic disorder of the NMJ
Myasthenia Gravis
What causes Myasthenia Gravis
antibody mediated attack of nicotinic Acetylcholine receptors on muscle membrane
What are the HLA haplotypes in MG
HLA B8 and DR3
What are the three characteristics of MG
- Fluctuating weakness
- Distribution of weakness (Ocular muscles)
- Clinical response to cholinergic drugs
What are the 4 MG classifications
- Purely Ocular (15-20%)
- Moderately Severe Generalized 25%
- Acute Fulminating (15%)
- Late severe (10%)
What are the lab findings in MG
anti-AChR in 80% of generalized
MUSK abs, LRP-4 abs
EMG - decremental response, increased jitter on single fiber
What is unique about the treatment of MG with steroids
start low dose and slowly increase to high dose
consider IgG or plasmapheresis in crisis pts
What is a myasthenic crisis
may occur spontaneously after infection
aspiration, diffuse weakness, respiratory failure
Stop anticholinesterase meds, use PLEX, IVIg
What is a cholinergic crisis
rare differential consideration
rapid increase in weakness
Big Clue: Miosis or fasciculations
if someone has Seronegative MG, what Ab are you looking for and how do you treat
MuSK (if negative look for LRP-4)
poor response to acetylcholine esterase meds
use PLEX, IVIg, Rituximab
What is Lambert-Eaton Myasthenic Syndrome
autoimmune attack against Voltage gated calcium channels on presynaptic nerve
Associated with SCCL
What is the clinical presentation of LEMS
Proximal weakness, loss of DTRs , dry mouth, impotent
Strength improves with exercise
What are the EMG findings in LEMS
low amplitude motor response that facilitate after exercise
Incremental response on fast repetitive stimulation
What is the clinical presentation of Botulism
toxin blocks release of ACh
Dry mouth, blurred vision, diplopia N/V
Treat with supportive care
