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440 Myasthenia Flashcards

1
Q

Neuromuscular junction (NMJ) disorder characterized by weakness and fatigability of skeletal muscles

A

Myasthenic gravis

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2
Q

what is the underlying defect in MG

A

decrease in the number of available acetylcholine receptors at the NMJ due to an antobody mediated autoimmune attack

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3
Q

Where is acetylcholine synthesize

A

motor nerve of the terminal and stored in vesicles of (quanta)

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4
Q

How many Ach vesicles are released during an action potentiation

A

150-200 vesicles are released and combined with AchR

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5
Q

how many subunits does an AchR have

A

5 subunits: 2a, 1beta, 1gamma, 1epsilon 1? arranged around a central core

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6
Q

Chief cation that produced depolarization

A

sodium

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7
Q

Addition pathophysiology MG aside from the decrease in available receptors

A

flattened or simplified postsynaptic folds leading to decreased efficiency of the neuromuscular transmission

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8
Q

refers to normal decline in amount of acetylcholine released on repeated activity

A

presynaptic rundown

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9
Q

what leads to myasthenic fatigue

A

presynaptic rundown and decrease in neuromuscular transmission leads to fewer and fewer mscule fiber activition with every succesive nerve impulses

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10
Q

what causes the autoimmune disorder in MG

A

anti AchR antibodies

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11
Q

how does this anti AcR antibodies reduce the number of receptors at the NMJ

A

acclerated turnover of AchR; damage to the postsynaptic muscle membrane by the antibody; blockade of the active site of the AchR

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12
Q

True or false. Thymus has a rule in the autoimmune response in MG

A

True.

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13
Q

True or false. The thymus is abnormal is 45% of patient with AchR antibody positive MG

A

False. As high as 75%

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14
Q

True or false. The thymus is hyperplastic in 65% of patients with MG

A

True. 10% have thymic tumors

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15
Q

Cardinal features of MG

A

weakness and fatigability

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16
Q

Describe the trend of muscle weakness in MG

A

weakness increases with repeated use or late in the day; and may improve with rest or sleep

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17
Q

Typically involved in the early course of MG

A

cranial muscles particularly the lids and extraocular muscles (EOM)

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18
Q

Initial complaints of MG

A

diplopia and ptosis

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19
Q

especially prominen tin MuSK antibody positive MG

A

bulbar weakness

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20
Q

Type of MG where weakness is restricted to the extraocular muscles for 3 years

A

ocular MG

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21
Q

Typical limb weakness in MG

A

proximal muscle and may be asymmetric

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22
Q

True or false. In MG, despite muscle weakness, deep tendon reflexes are preserved

A

True.

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23
Q

When is a patient with MG is said to be in crisis

A

when ventilatory weakness required respiratory assitance

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24
Q

What is the ice pack test in MG

A

when an ice pack is applied over a ptotic eye and it improved then it is due to an NMJ defect

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25
Virtually diagnostic of MG
presence of anti AchR antiboides
26
A small portion of MG patients without antibodies to AchR or to MuSK have antibodies to what
LRP4
27
May provide helpful diagnostic evidence of MG
repetitive nerve stimulation; there is rapid reduction of more than 10% in the amplitude of evoked responses in MG
28
How long should anti AchE medication be stopped prior to repetitive nerve stimulation
6-12 hours before testing
29
Used commonly for diagnostic testing for MG
edrophonium is used with rapid onset of 30 s and short duration of 5 minutes
30
How is the edrophonium test done
2 mg of edrophonium is given, if there is improvement of ptosis or muscle weakness it is considered positive and it terminated. If no improvement occurs, another 8 mg IV edrophonium is given. If improvement occurs then it considered postiive.
31
comprise a rare heterogenous group of disorders of the NMJ that are not immune mediated but due to genetic mutations in any component of the NMJ
congenital myasthenic syndromes (CMS)
32
presynaptic disorder of the NMJ that can cause weakness similar to that of the MG
Lambert-Eaton myasthenic syndrome (LEMS)
33
Muscles commonly affected in LEMS
proximal muscles of the lower limbs
34
How is MG differentiated from LEMS
in LEMS, reflexes are depressed or absent and patient experience autonomic change such as dry mouth and impotence
35
what is the cause of LEMS
autoantibodies against P/Q type calcium channels at the motor nerve terminals
36
in older adults, LEMS is associated with what and most commonly what
LEMS is associated with malignancy most commonly small cell lung cancer (SCLC)
37
what is the mechanism of action of pyridostigmine
prolongs the action of the Ach allowing repeated interactions with the AchR
38
differential for MG which is due to potent bacterial toxin
botulism
39
how does this toxin lead to MG like manifestations
the toxins cleave specific proteins for the release of Ach from the motor nerve terminal and thus interfere with the NMJ transmission
40
historic term for a myasthenic like fatigue syndrome without an organic basis
neurasthenia
41
a rare condition resulting in EOM weakness and weakness of the proximal muscles of the limbs and other systemic feature. Muscle biopsy reveals mitochondrial disorders
Progressive external opthalmoplegia
42
most widely used anticholinesterase drug and what dose it is initiated
Pyridostigmine 30-60 mg 3x-4x per day
43
what is the onset of action and duration of pyridostigmine
onset within 15-30 mins and last from 3-4 hours
44
maximum dose of pyridostigmine
300 mg per day
45
when can immunosuppresion be seen to produce clinical improvement
glucocorticoids, tacrolimus and cyclosporine generally produce clinical improvements within a period of 1-3 months
46
True or false. To minimize adverse side effects, prednisone should be given in a single dose rather than in divded doses throughout the day
True.
47
dosage of prednisone for patient with mild or moderate weakness
15-25 mg/day
48
how is prednisone dose adjusted
dose in increased in stepwise manner as tolerated at 5 mg/day at 2-3 days intervals until marked improvement or at a dose of 50-60 mg/day
49
true or false. In MG patients with severe weakness and those already hospitalized, starting at high dose is reasonable
True.
50
how is prednisone tapered
no faster than 10 mg a month until 20 mg daily and then by 2.5-5 mg a month
51
other immunotherapy for MG which widely used because of its presumed effectiveness and relative lack of side effects
myocphenolate mofetil at 1-1.5 g BID
52
given to reduce the dosage of prednisone necessary to control the symptoms of MG
azathiorprine initially at 50 mg/day for about a week before increasing the dose
53
how is azathioprine dosage adjusted
initially at 50 mg/day for a week and if no side effect increased gradually until 2-3 mg/kg per day dose is achieved or once there is leukopenia of 3000-4000/uL
54
one drug not to be given together with azathioprine and why
allopurinol is not given together as both drug lead to bone marrow suppresion
55
calcineurin inhibitors effective in MG but what is one major downside
cyclosporine and tacrolimus
56
what is the dosage and therapeutic level of cyclosporine
4-5 mg/kg per day; trough level of 150-200 ng/L
57
what is the dose and trough level of tacrolimus
tacrolimus at 0.07-1.0 mg/kg/day with trough at 5-15 ng/L
58
monoclonal antibody showing its benefit in MG
rituximab is particularly effective in MuSK antibody postive MG
59
what is the dosing of rituximab
1 g IV 2x at 2 weeks apart
60
given to refractory MG by inducing a reboot of the immune system
cyclophosphamide
61
how is plasmapharesis done for MG
5 exchanges (3-4 L per exchange) is administered over a 10- to 14- day period to mechanically separate the pathogenic antibodies
62
how is IVIg given
2 g/k administered 2-5 days
63
most common cause of crisis
intercurrent infection
64
True or false. Approx 20% of patients with MG can be tapered off all immunotherapies and achieve sustained remission. Mortality rate is at 1-2%
True.

Neurology (14 decks)

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