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NEURO CLERKSHIP > Neuromuscular Junction > Flashcards

Neuromuscular Junction Flashcards

1
Q

Which structures may be involved in the pathology of a neuromuscular disease?

A
  1. Muscle
  2. Neuromuscular Junction
  3. Peripheral Nerve + Cranial Nerves
  4. Spinal Nerve Root
  5. Nerve Plexus
  6. Nuclei in the brainstem or spinal cord
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2
Q

What is the most common NMJ disease?

A

Myasthenia Gravis

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3
Q

What are some examples of neuromuscular junction diseases (4)?

A
  1. Myasthenia Gravis
  2. Lambert-Eaton
  3. Botulism
  4. Tetanus
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4
Q

What is the age distribution for Myasthenia Gravis?

A

Bimodal- teens-30 (females) and 50-70 (males)

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5
Q

What is seen histologically at the nerve terminal in Myasthenia Gravis?

A

No invaginations of the nerve terminal

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6
Q

What are the three pathological causes of MG?

A
  1. Blocking
  2. Accelerated Internalization of ACh Receptors
  3. Complement lysis of the muscle end plate
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7
Q

Describe the blocking pathology of MG

A

Direct blocking of the skeletal muscle nicotinic ACh Receptor site by antibodies

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8
Q

Describe the accelerated internalization pathology of MG

A

ACh Receptors are more rapidly internalized and degraded due to the cross linking of IgG Antibodies

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9
Q

Describe the role of complement in MG

A

Complement mediated lysis results in distortion of the muscle end plate (fewer invaginations/less surface area)

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10
Q

Which pathophysiological cause of MG describes the decreased effectiveness of medications with time?

A

Complement destruction of the muscle end plate

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11
Q

50% of AChR Antibody + MG patients have what finding?

A

Thymic hyperplasia

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12
Q

What percent of MG patients have thymic tumors?

A

10-15%

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13
Q

How does a hyper plastic thymus correlate to MG?

A

Thymocytes can produce anti-ACh Receptor Antibodies

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14
Q

Typical presentation of MG

A

Fatiguable weakness often affecting the extra ocular, oropharyngeal, axial or limb muscles

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15
Q

How will reflexes be on a patient with MG?

A

Normal

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16
Q

How will the sensory exam be on a patient with MG?

A

Normal

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17
Q

What are the three types of MG and which muscle groups are involved with each?

A

Bulbar- Craniofascial weakness
Ocular- EOM
General- Entire body

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18
Q

Which EOM is usually most severely involved?

A

Medial Rectus

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19
Q

What is tested for by having the patient count aloud?

A

MG- enhances dysarthria

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20
Q

What are the clinical fatiguing maneuvers used to test for MG?

A
  1. Sustained Upgaze
  2. Sustained aBduction of the arms
  3. Sustained elevation of the leg while laying supine
  4. Repeated arising from chair w/o arms
  5. Counting aloud
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21
Q

Bulbar MG will be detected by

A

Changing pitch while counting aloud

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22
Q

What is the most common immunologic finding in MG?

A

ACh Receptor Binding Antibody

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23
Q

What percent of MG patients have the AChR Binding Antibody?

A

80-85%

as low as 50% in some ocular cases

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24
Q

Why is the AChR binding antibody the gold standard?

A

Low false positive rate (high specificity)

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25
Q

What is the anti-muscle specific tyrosine kinase?

A

A Neuromuscular Junction protein that clusters ACh Receptors

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26
Q

Which patients may test positive for anti-muscle specific tyrosine kinase?

A

Generalized MG patients

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27
Q

What percent of patients who test (-) for ACh Receptor Binding Antibody test + for the Anti-muscle specific tyrosine kinase?

A

Up to 40%

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28
Q

Which antibody is highly associated with thymomas in MG?

A

Anti-striated muscle

29
Q

When do you test for the anti-striated muscle antibody?

A
  1. Young patients as an adjunct way to detect thymomas

2. Older patients with mild disease (because this may be the only abnormality)

30
Q

Repetitive Nerve Stimulation is more sensitive in diagnosing which type of MG?

A

Generalized MG

31
Q

What is the next step if the RNS is normal but the patient has symptoms of MG?

A

Do a single fiber electromyography (SFEMG)

32
Q

Describe the EMG findings in MG

A

The end plate potential (EPP) is decreased in MG and there is a lower safety factor; repeated stimulation –> the EPP to fall below threshold needed for muscle fiber activation

33
Q

How does the edrophonium test work?

A

IV administration of edrophonium (ACh Esterase Inhibitor) results in rapid improvement of ptosis/weakness and only lasts 5-10mins

34
Q

What is the sensitivity of the edrophonium test?

35
Q

What are potential drawbacks to the edrophonium test?

A
  1. Must blind physicians
  2. Bradycardia and Hypotension (keep Atropine close)
  3. Not specific/reliable
36
Q

What is the symptomatic treatment of MG?

A

Pyridostigmine (Mestinon)

37
Q

What drug class is pyridostigmine?

A

ACh Esterase Inhibitor

38
Q

What is the effect of pyridostigmine?

A

It increases the size and length of the end plate potential within 30mins and lasts 3-6hrs

39
Q

What are common side effects of pyridostigmine?

A
  1. Stomach Cramps/Diarrhea/Nausea/Vomiting
  2. Sweating
  3. Bronchial and nasal secretions
  4. Bradycardia
40
Q

What are the general types of treatments for MG?

A
  1. Symptomatic

2. Immunosuppressant (short and long term)

41
Q

What are short term immunotherapies used for MG?

A

Plasma Exchange and IV Ig

42
Q

What are the long term immune-directed therapies for MG?

A
  1. Thymectomy
  2. Corticosteroids
  3. Azathioprine and Mycophenolate
43
Q

How is plasma exchange used to treat MG?

A

It temporarily reduces the levels of circulating antibodies

44
Q

When do patients experience relief from plasma exchange for MG and how often are treatments?

A

Relief in days, usually receive 3-6 exchanges every other day

45
Q

Why is plasma exchange not done daily?

A

It depletes clotting factors

46
Q

When is plasma exchange done for MG?

A
  1. Acute Exacerbations

2. Drug resistant patients

47
Q

What is the MOA of IV Ig?

A

Either neutralizing or down regulation

48
Q

When will an MG patient experience relief on IV Ig and how long does it last?

A

Relief in days, effects last 4-8 weeks

49
Q

What is the dosing of IV Ig?

A

2g/kg given over 2-5 days

50
Q

When is IV Ig used?

A

Similar to PLEX-

  1. Acute Exacerbations
  2. Drug Resistant patients
51
Q

What is the indication for a thymectomy in an MG patient?

A
  1. Thymoma (only absolute indication)

2. Usually in patients under 50

52
Q

Which percent of SCLC patients will have LEMS?

53
Q

What percent of LEMS have an identifiable malignancy?

54
Q

Which patients develop LEMS who do not have SCLC?

A

Young females with other autoimmune diseases

55
Q

Describe the pathophysiology of LEMS

A

IgG antibody binds to voltage gated Ca++ Channels in the presynaptic neuron

56
Q

How does the antibody to VGCC cause LEMS?

A

Thought that the antibodies cross link multiple VGCCs which renders them ineffective by disrupting their proper positioning and function

57
Q

How does SCLC cause LEMS?

A

An antigen that is expressed in SCLC results in the formation of VGCC antibodies

58
Q

What is the consequence of decreased Ca++ influx into the presynaptic cell?

A

Decreased ACh released into the neuromuscular junction –> decreased end plate potential –> failed transmission

59
Q

What are the clinical symptoms of LEMS?

A
  1. Slow progressive proximal leg and arm weakness
  2. Tender/Aching
  3. Mild bulbar (cranial nerve) and respiratory symptoms
  4. Dry Mouth and Metallic Taste
  5. Weakness of Ca++ Channel Blocker meds
  6. Prolonged paralysis prior to intubation
60
Q

When does LEMS present in SCLC patients?

A

Up to 9 months before detection of the cancer

61
Q

What will be seen on physical exam for LEMS?

A
  1. Proximal weakness that improves with exercise
  2. Minimal Bulbar Findings (ptosis, blurred vision, difficulty chewing, dysphagia, dysarthria)
  3. Dry eyes and Dry mouth
62
Q

How will the sensory exam of a LEMS patient be?

63
Q

How will the reflexes be of a LEMS patient?

A

Reduced/absent

64
Q

How is LEMS diagnosed?

A
  1. Serum testing of voltage gates calcium channel antibody

2. Electrodiagnostic testing (repetitive stimulatio; 3Hz- decrement; 30-50Hz results in increment)

65
Q

Which disease (MG or LEMS) presents with a weakness that has fluctuation?

66
Q

Which disease (MG or LEMS) presents with autonomic issues?

67
Q

What is the treatment for LEMS?

A
  1. Symptomatic and immunosuppressive

2. PLEX or IV Ig

68
Q

What is the most common cause of myopathy?

A

Statins (followed by inclusion body, MG, poly/dermatomyositis and DMD)

NEURO CLERKSHIP (10 decks)

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