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Neurology > 440 Myasthenia > Flashcards

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
Q

Virtually diagnostic of MG

A

presence of anti AchR antiboides

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26
Q

A small portion of MG patients without antibodies to AchR or to MuSK have antibodies to what

A

LRP4

27
Q

May provide helpful diagnostic evidence of MG

A

repetitive nerve stimulation; there is rapid reduction of more than 10% in the amplitude of evoked responses in MG

28
Q

How long should anti AchE medication be stopped prior to repetitive nerve stimulation

A

6-12 hours before testing

29
Q

Used commonly for diagnostic testing for MG

A

edrophonium is used with rapid onset of 30 s and short duration of 5 minutes

30
Q

How is the edrophonium test done

A

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
Q

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

A

congenital myasthenic syndromes (CMS)

32
Q

presynaptic disorder of the NMJ that can cause weakness similar to that of the MG

A

Lambert-Eaton myasthenic syndrome (LEMS)

33
Q

Muscles commonly affected in LEMS

A

proximal muscles of the lower limbs

34
Q

How is MG differentiated from LEMS

A

in LEMS, reflexes are depressed or absent and patient experience autonomic change such as dry mouth and impotence

35
Q

what is the cause of LEMS

A

autoantibodies against P/Q type calcium channels at the motor nerve terminals

36
Q

in older adults, LEMS is associated with what and most commonly what

A

LEMS is associated with malignancy most commonly small cell lung cancer (SCLC)

37
Q

what is the mechanism of action of pyridostigmine

A

prolongs the action of the Ach allowing repeated interactions with the AchR

38
Q

differential for MG which is due to potent bacterial toxin

A

botulism

39
Q

how does this toxin lead to MG like manifestations

A

the toxins cleave specific proteins for the release of Ach from the motor nerve terminal and thus interfere with the NMJ transmission

40
Q

historic term for a myasthenic like fatigue syndrome without an organic basis

A

neurasthenia

41
Q

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

A

Progressive external opthalmoplegia

42
Q

most widely used anticholinesterase drug and what dose it is initiated

A

Pyridostigmine 30-60 mg 3x-4x per day

43
Q

what is the onset of action and duration of pyridostigmine

A

onset within 15-30 mins and last from 3-4 hours

44
Q

maximum dose of pyridostigmine

A

300 mg per day

45
Q

when can immunosuppresion be seen to produce clinical improvement

A

glucocorticoids, tacrolimus and cyclosporine generally produce clinical improvements within a period of 1-3 months

46
Q

True or false. To minimize adverse side effects, prednisone should be given in a single dose rather than in divded doses throughout the day

A

True.

47
Q

dosage of prednisone for patient with mild or moderate weakness

A

15-25 mg/day

48
Q

how is prednisone dose adjusted

A

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
Q

true or false. In MG patients with severe weakness and those already hospitalized, starting at high dose is reasonable

A

True.

50
Q

how is prednisone tapered

A

no faster than 10 mg a month until 20 mg daily and then by 2.5-5 mg a month

51
Q

other immunotherapy for MG which widely used because of its presumed effectiveness and relative lack of side effects

A

myocphenolate mofetil at 1-1.5 g BID

52
Q

given to reduce the dosage of prednisone necessary to control the symptoms of MG

A

azathiorprine initially at 50 mg/day for about a week before increasing the dose

53
Q

how is azathioprine dosage adjusted

A

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
Q

one drug not to be given together with azathioprine and why

A

allopurinol is not given together as both drug lead to bone marrow suppresion

55
Q

calcineurin inhibitors effective in MG but what is one major downside

A

cyclosporine and tacrolimus

56
Q

what is the dosage and therapeutic level of cyclosporine

A

4-5 mg/kg per day; trough level of 150-200 ng/L

57
Q

what is the dose and trough level of tacrolimus

A

tacrolimus at 0.07-1.0 mg/kg/day with trough at 5-15 ng/L

58
Q

monoclonal antibody showing its benefit in MG

A

rituximab is particularly effective in MuSK antibody postive MG

59
Q

what is the dosing of rituximab

A

1 g IV 2x at 2 weeks apart

60
Q

given to refractory MG by inducing a reboot of the immune system

A

cyclophosphamide

61
Q

how is plasmapharesis done for MG

A

5 exchanges (3-4 L per exchange) is administered over a 10- to 14- day period to mechanically separate the pathogenic antibodies

62
Q

how is IVIg given

A

2 g/k administered 2-5 days

63
Q

most common cause of crisis

A

intercurrent infection

64
Q

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%

A

True.

Neurology (14 decks)

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