440 Myasthenia Flashcards
Neuromuscular junction (NMJ) disorder characterized by weakness and fatigability of skeletal muscles
Myasthenic gravis
what is the underlying defect in MG
decrease in the number of available acetylcholine receptors at the NMJ due to an antobody mediated autoimmune attack
Where is acetylcholine synthesize
motor nerve of the terminal and stored in vesicles of (quanta)
How many Ach vesicles are released during an action potentiation
150-200 vesicles are released and combined with AchR
how many subunits does an AchR have
5 subunits: 2a, 1beta, 1gamma, 1epsilon 1? arranged around a central core
Chief cation that produced depolarization
sodium
Addition pathophysiology MG aside from the decrease in available receptors
flattened or simplified postsynaptic folds leading to decreased efficiency of the neuromuscular transmission
refers to normal decline in amount of acetylcholine released on repeated activity
presynaptic rundown
what leads to myasthenic fatigue
presynaptic rundown and decrease in neuromuscular transmission leads to fewer and fewer mscule fiber activition with every succesive nerve impulses
what causes the autoimmune disorder in MG
anti AchR antibodies
how does this anti AcR antibodies reduce the number of receptors at the NMJ
acclerated turnover of AchR; damage to the postsynaptic muscle membrane by the antibody; blockade of the active site of the AchR
True or false. Thymus has a rule in the autoimmune response in MG
True.
True or false. The thymus is abnormal is 45% of patient with AchR antibody positive MG
False. As high as 75%
True or false. The thymus is hyperplastic in 65% of patients with MG
True. 10% have thymic tumors
Cardinal features of MG
weakness and fatigability
Describe the trend of muscle weakness in MG
weakness increases with repeated use or late in the day; and may improve with rest or sleep
Typically involved in the early course of MG
cranial muscles particularly the lids and extraocular muscles (EOM)
Initial complaints of MG
diplopia and ptosis
especially prominen tin MuSK antibody positive MG
bulbar weakness
Type of MG where weakness is restricted to the extraocular muscles for 3 years
ocular MG
Typical limb weakness in MG
proximal muscle and may be asymmetric
True or false. In MG, despite muscle weakness, deep tendon reflexes are preserved
True.
When is a patient with MG is said to be in crisis
when ventilatory weakness required respiratory assitance
What is the ice pack test in MG
when an ice pack is applied over a ptotic eye and it improved then it is due to an NMJ defect
Virtually diagnostic of MG
presence of anti AchR antiboides