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Module 3 > Myasthenia Gravis > Flashcards

Myasthenia Gravis Flashcards

1
Q

What is the defining feature of MG?

A

painless muscle weakness that gets worse with use

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2
Q

What are the causes of myasthenia gravis?

A

idiopathic; drugs e.g penicillamine; congenital myasthenias

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3
Q

What is the difference in gender balance with MG in young vs old age groups?

A

in young: women are affected twice as much as men but in older its equal

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4
Q

What are the 3 main types of MG?

A

ocular; bulbar; generalised

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5
Q

How does ocular MG present?

A

ptosis and double vision

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6
Q

What defines ocular MG?

A

affects eyes only for >2 year s

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7
Q

What is a major differential for ocular MG?

A

chronic progressive external opthalmoplegia- mitochondrial disorder

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8
Q

How does bulbar MG present?

A

dysphagia/dysarthria; weight loss; chest infections

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9
Q

what age group is affected more often with bulbar MG?

A

older patinets

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10
Q

What is hte major differential for bulbar MG?

A

MND

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11
Q

When do generalised MG patients typically present?

A

post op or intensive care

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12
Q

What is the tensilon test?

A

edrophonium blocks the breakdown of ACh, if muscle strenght gets better in the muscle group

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13
Q

What is the main issue with ocular MG if the patietns are generally well?

A

can get worse if get other illness and drugs etc

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14
Q

What is seen at hte NMJ of MG patients?

A

have fewer ACh receptors

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15
Q

Who mainly uses the ice pack test?

A

opthalmologists

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16
Q

How does the icec pack test work?

A

ice pack over ptotic eyelid for 2 minutes, if there is an improvement in ptosis of 2mm-diagnostic

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17
Q

How does EMG in the diagnosis of MG work?

A

repetitively stimulate the muscle to deplet it of ACh and stimulated muscle contraction gets weaker by at least 20%

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18
Q

What is the function of single fibre EMG?

A

gold standard - tests for failure of faulty NMJ function

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19
Q

What type of ACh receptor is blocked by autoantibodies in MG?

A

nicotinic not muscarinic

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20
Q

what is the problem with anti-ACh-esterases?

A

they block both nicotinic and muscarinic receptors which causes problems in the gut

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21
Q

What is given to ameliorate the gut problems seen with anti-ACh esterases?

A

propanthelline

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22
Q

How many patients with MG have a positive antibody?

A

70%

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23
Q

Which form of MG is antibody more common in?

A

generalised MG

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24
Q

How many thymoma patients develop MG?

A

1/3rd

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25
Q

What other type of antibody is common in thymoma cases?

A

antistriational

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26
Q

What is the main stay of acute severe treatment for MG>

A

plasma exchange

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27
Q

What is the remission rate for thymectomy in MG?

A

40-60% at 7-10 years

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28
Q

What are the symptoms of lambert eaton syndrome?

A

proximal muscle weakness; fatiguability; dry mouth and impotence

29
Q

What is LEMS associated iwth?

A

small cell lung cancer

30
Q

What are the antibodies to in LEMS?

A

presynaptic calcium channels

31
Q

Why does LEMS improve with use?

A

with enough stimulation, calcium gets through allowing ACH release

32
Q

What suggested taht there was a problem with antibodies in seronegative MG?

A

still responded to plasma exchange adn immunosuppression

33
Q

What antibodies were found in seronegative MG?

A

muscle specific kinase antibodies

34
Q

What is the first line symptomatic treatment for MG?

A

pyrostigmine

35
Q

How does pyrostigmine work?

A

blocks breakdown of ACh by blocking ACh esterase

36
Q

Why are steroids often given initially in hospital to MG patietns?

A

can make MG deteriorate if given at high doses too quickly

37
Q

What immunotherapy is give nfor MG?

A

azathioprine

38
Q

How long does azathioprine take to work?

A

6-12 months

39
Q

What are the SE of azathioprine?

A

nausea; stomach problems; bone marrow suppression- regular bloods

40
Q

What is the function of immunoglobulins in the acute treatment of MG?

A

blocks the effects of antibodies

41
Q

When are immunoglobulins used in MG?

A

acute severe relapses in pregnancy/ post op

42
Q

What is thought to be the cause of such high association of thymomas and thymic hyperplasia in MG?

A

loss of negative regulation- cortex is maintained in thymoma but medulla lost; very low expression of AIRE in thymomas

43
Q

What factors are thought to play roles in patients with anti-AChr antibodies?

A

thymic abnormalities; defects in immune regulation; sex hormones

44
Q

What is the structure of the ACHr?

A

five protein chains that are arranged in a long tube

45
Q

What is the target of hte anti-ACHr antibodies?

A

alpha chains have binding sites for acetylcholine on the external side and contain the primary immunogenic region

46
Q

What is the primary mechanism of hte reduced ACHRs at hthe NMJ of MG patients?

A

destruction of the postsynaptic membrane by complement pathway activation leading to generation of MAC

47
Q

What is the difference between early onset and late onset MG?

A

early onset present with high level of ACHr ab and thymic follicular hyperplasia caharacterised by ectopic germinal centres- 80% women; late onset is associated with thymoma and anti-striated mucscle antibodies –more severe and generalised

48
Q

What is hte function of muscle specific kinase?

A

plays a major role in the development of the NMJ and is essential for clustering of ACHr- no aggregates of ACHrs are seen in its absence

49
Q

What is a newly identified antibody target in MG?

A

anti-LRP4 antibodies

50
Q

What is the function of the LRP4 protein?

A

receptor for the neural agrin that activates MuSK and AChR clustering

51
Q

What are the thymomas caused by?

A

abnormal development of epithelial cells- medullary vs cortical

52
Q

How are thymomas thought to relate to MG onset?

A

thymic medulla is site of neg selection- in thymoma, effective deletion of autoreactive T cells doesn’t occur; also- lack of AIRE, FOXP3 and MHC-II antigens

53
Q

What demonstrates that in thymic follicular hyperplasia the MG thyus contains B cells producting anti-AChR antibodies?

A

thymic tissue or thymic cells frmo the AChR-MG patients can induce the production of antibodies against AChR in immunodeficient mice and the loss of AChR at the muscle endplates

54
Q

What other autoimmune dieases have ectopic GCs been described in?

A

salivary glands in Sjogrens; joints in RA; meninges in secondary progressive MS–thymuc is the inflamed tissue in AChR-MG patients

55
Q

What was the inflammatory state of hte MG thymus demonstrated by?

A

overexpression of numberus IFNy induced genes

56
Q

What indicates that both Th1 and Th2 cells are involved in MG?

A

have larger numbers of cells that express IFNy or IL-4

57
Q

What does the activation of the immune system in MG patients suggest?

A

presence of a number of inflammatory signs suggests taht the efficiency of immune regulation mechanisms is compromised

58
Q

What is seen with the Tregs in MG?

A

severe defects in their suppressive function when cultured with CD4 cells and other PBMCs

59
Q

What suggests that Th1 and Th17 cells are involved in the pathology of MG?

A

higher levels of IL-17 in serum; many genes in the IL-17 family are increased in MG Tregs - tregs themselves are frive to secrete pro-inflammatory IL-17

60
Q

Give an overview of a model of the pathogenic mechnisms in MG leading to thymic hyperplasia?

A

triggering event e.g viral infection in genetically favourable environment–thymic epithlium overprduce IL-1; IL-6 and IFNb and lymphocytes produce TNFa and IFNy- increase MHC-II; AChR and chemokines which attract B cells. estrogens proote B cell proliferation- inflammatory mileu modulates the T cell phenotype- Tregs produce Th17; all T cells produce IFNy; TNfa; IL-21;IL17 favouring Tfh development and generation of GCs. Tregs become inefficient in inflam environment and T cells resistant to suppression

61
Q

What is thought to be the reason for reduced severity and remission with thymectomy?

A

eliminates the main site of anti-AChR autoantibody production and leads to decreased AChR

62
Q

What is the MZ concordance of MG?

A

35%

63
Q

What are the HLA associations?

A

HLA-B8; HLA-DR3

64
Q

What is the PTPN22 gene?

A

member of the tyrosine phosphatase subfamily and intereferes with signalling in T cells leading to inhibition of T cell activation

65
Q

What are microRNAs?

A

small non-coding RNAs that mediate post-transcriptional silencing of target genes

66
Q

What is the significance of miRNAs in autoimmune disease generally?

A

dysregulation has been described in a variety of AI diseases

67
Q

Is there a role for miRNAs in MG?

A

there was a decrease in miR-320a levels- correlated with increases in levels of pro-inflammatory cytokines–miR-320a regulates ERK pathway

68
Q

What is the function of estrogen in autoimmune disease?

A

favour processes involving CD4 Th2 cells nad B cells-B cell mediated AI disease- allows autoreactive B cells to escape? however other studies suggest that they promote Th1 responses—complex roles based on dose, timing, microenvionment

69
Q

What needs further addressing in MG?

A

role of miRNAs in the modulation of immune function; there has been recent research on the importance of physical exercise in MG, where there are no guidelines- previously been restricted , suggests that symptoms can be improved

Module 3 (33 decks)

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