Disorders of the Neuromuscular Junction Flashcards
autoimmune disorder that is characterized as muscle weakness due to dysfunction of the neuromuscular junction
myasthenia gravis
the most common disorder of neuromuscular transmission
myasthenia gravis
myasthenia gravis in which autoantibodies attack the acetylcholine receptor, resulting in reduction of the number of receptors over time
seropositive
myasthenia gravis in which the patient has no detectable levels of autoantibodies against acetylcholine receptors
seronegative
what antibodies may be present in patients with seronegative myasthenia gravis?
antibodies directed against MuSK
presents at birth as weakness due to the mother with myasthenia gravis who passes antibodies through the placenta
congenital myasthenia
what is the cardinal feature of myasthenia gravis?
fluctuating skeletal muscle weakness
when does the skeletal muscle weakness get worse or improve?
worse later in day or with exercise
improves with rest
what are the 2 clinical forms of weakness in myasthenia gravis?
ocular
generalized
what is the presentation called when a patient cannot pull facial muscles into a complete smile?
myasthenic sneer
what is the presentation called when myasthenia gravis affects the neck muscles?
dropped head syndrome
what does myasthenia gravis of the respiratory muscles cause? and what could cause this (4)?
myasthenic crisis
surgery
infection
medications
tapering immunosuppression
what will NOT change in myasthenia gravis? (2)
sensation
reflexes
what is the diagnostic criteria for myasthenia gravis? (2)
fatigability/weakness of muscle + improvement with anticholinesterase drugs
what diagnostic can test ptosis in myasthenia gravis?
ice pack test will improve ptosis
what are the 3 serologic tests for myasthenia gravis?
acetylcholine receptor antibodies
MuSK antibodies
autoimmune thyroid labs
why would we do a chest CT in myasthenia gravis?
to look for thymoma
what are 2 electrophysiologic studies for myasthenia gravis?
repetitive nerve stimulation studies
single-fiber electromyography (EMG)
what is the 1st line treatment for myasthenia gravis in a stable patient?
oral anticholinesterase (pyridostigmine)
what should we watch for when using pyridostigmine?
cholinergic crisis
what is the 2nd line treatment for myasthenia gravis in a stable patient? (2)
chronic immunosuppressive agents:
azathioprine
oral glucocorticoid
what are 2 options for treatment of myasthenia gravis in patient who is in potential crisis?
plasmapheresis
IVIG
what are the 3 uses for plasmapheresis and IVIG?
myasthenic crisis
preop before thymectomy
bridge to slower acting immunotherapies
what can be done for a patient with myasthenia gravis in a case of thymoma or nonthymomatous autoimmunity?
thymectomy
what must be done before performing a thymectomy on a patient?
control weakness first
what is the clinical course of myasthenia gravis? (2)
symptom-free periods are lost
progression peaks withing few years of onset
myasthenic syndrome associated with small cell carcinoma characterized by weakness of proximal limb muscles that improves with activity
lambert-eaton syndrome
what is the diagnostic for lambert-eaton syndrome?
EMG
what is the treatment for lambert-eaton syndrome? (3)
plasmapheresis
+
immunosuppressants
prednisone
azathioprine
toxin of Clostridium b. that prevents the release of acetylcholine at the neuromuscular junctions and autonomic synapses
botulism
a patient with botulism will most likely have what in their history?
hx of ingestion of possibly contaminated canned food 72 hrs prior
a patient presents with diplopia, dilated pupils, ptosis, facial weakness, dysphagia, respiratory difficulty, limb weakness, and postural hypotension. what are they likely experiencing?
botulism
what will likely be seen in botulism if we do an electrophysiological study?
increased muscle response to fast rate stimulation
what is the treatment for botulism?
3,4 diaminopyridine (K channel blocker)
