Disorders of the NMJ Flashcards
What is MYasthenia Gravis?
Defect of neuromuscular transmission due to an antibody-mediated attack upon nicotinic acetylcholine receptors on muscle membrane
While most cases of MG are sporadic, what haplotypes are most associated?
HLA B8 and DR3
What other autoimmune disorders are associated with MG?
SLE, RA, thyroid disorders, etc.
In which populations is MG more common?
Young women and older men
What are the three general characteristics of MG?
- Fluctuating weakness
- Ocular muscle weakness, dysarthria, dysphagia, limb/neck weakness
- Respond to cholinergic drugs
What are the 4 classifications of MG?
I: Purely ocular
II: Moderately severe, generalized (most common)
III: Acute fulminating
IV: Late severe
What lab data will you see with MG?
Anti-AChR Abs
MUSK and LRP-4 AB
What EMG findings will you see with MG?
- Decremental response on repetitive stimulation
- Increased “Jitter” on single fiber EMG
What are some speciality or clinical tests done to assess for MG?
Tensilon (edrophonium test)-rarely done
Fatigable weakness/ice bag test, Cogan’s sign
What are some general treatments for MG?
Anticholinesterase drugs (Mestinon)
Prednisone
Immunosuppressants, IVIG
Thymectomy
What is myasthenic crisis?
What can trigger it?
What can it cause?
What is the treatment?
rapid deterioration of the disease itself
- can be spontaneous after infections/drug use
- can cause aspiration, diffuse weakness, resp. failure
- treat by stoping anticholinesterase meds, use PLEX, IVIG, maybe steroids
What is cholinergic crisis?
rapid increase in weakness from excess anticholinesterase meds
- Sx include N/V, sweating, salivation, colic, diarrhea, bradycardia
- BIG CLUE: miosis and or fasciculations
What ab will be seen in Seronegtive MG?
What are the three types?
10% will have no anti-AChR Abs, and 40% of these will have MUSK abs
- Oculopharyngeal weakness
- Neck, shoulder, resp. weakness
- Indistinguishable from Ab + MG
What is the treatment for seronegative MG?
PLEX, IVIG, and Rituximab is best
Remission is possible
Poor response to anticholinesterase meds/thymectomy
What is Lambert-Eaton Myasthenic Syndrome?
Autoimmune attack against voltage-gated calcium channels on the presynaptic nerve terminal
Leads to weakness
Often associated with cancer (SCCL)
What is the clinical presentation of LEMS?
Proximal weakness, loss of DTRs, myalgias, dry mouth, impotence
Oropharyngeal/ocular muscles may be affected, but not like MG
Strength may improve after exercise
May have slight response to Tensilon test
What Lab data is expected with LEMS?
Anti-VGCC Abs
What are the EMG findings associated with LEMS?
Low amplitude motor response that facilitates after a brief period of exercise
Incremental response on fast repetitive stimulation
What is the treatment for LEMS?
- treat malignancy
- Acetylcholinesterase inhibitors
- Amifampridine/3-4 Diaminopyridine/Gaunidine hydrochloride
- Immunosuppressents/IVIG
What is the clinical presentation of Botulism?
Toxin blocks presynaptic release of Ach
Presents with dry mouth, blurred vision, N/V, hypohidrosis, muscle paralysis
What is the treatment for botulism?
ICU monitoring with resp. support
Antitoxin or Guanidine Hydrochloride
What are the symptoms of Sarin and VX nerve gases?
Inhibit Achesterase at NMJ to cause end organ overstimulation
Miosis, secretions, bronchospasm, cramps, N/V/D, HR/BP changes, muscular weakness, SZs, LOC
Death by resp. failure
What is the treatment for Sarin or VX gas?
Decontamination
Resp. support
Atropine 2-6mg q 5-10 min until secretions recede
2-Pralidoxime chloride: 1gm IV over 20-30 minues
Szs-benzos
