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NUR 202 Week 7 > Progressive Neuromuscular Disorders Pt 3: MG > Flashcards

Progressive Neuromuscular Disorders Pt 3: MG Flashcards

1
Q

MG: Epidemiology

  • Motor disorder characterized by fluctuating, localized skeletal muscle weakness & fatigue
  • Acquired autoimmune dz
A

MG: Pathophysiology

Presents as 1 of 3 serotypes
▻ Anti-AChR
▻ MuSK
▻ Seronegative MG (SNMG)

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2
Q
  • An acquired autoimmune neuromuscular junction disorder, is c/b antibodies that are directed toward skeletal muscle nicotinic ACh receptors & muscle-specific kinase
A
  • Is the most treatable of the chronic neurologic disorders
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3
Q
  • May be made worse by or induced by penicillamine (Cuprimine), used in the treatment of RA, but in most cases is idiopathic
  • Course varies from mild, w/ocular sx’s of ptosis & diplopia, to severe cases w/generalized weakness & resp involvement
A
  • Is c/b an autoimmune process in which antibodies attack acetylcholine (ACh) receptors, resulting in a dec # of ACh receptor (AChr) sites @ the neuromuscular junction
  • ACh lvls are ok, just prevented from binding w/the receptor sites
  • AChE acetylcholinesterase is the enzyme that normally terminates this activity
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4
Q

Clinical Manifestations

  • Ocular, bulbar, or generalized presentations
    > Diplopia (result of EOM weakness)
    > Ptosis (unilat or bilat)
  • Often seek medical care for muscular weakness/fatigue
A
  • Weakness in facial & throat muscles - bland facial expression, dysphonia
  • Generalized weakness - affecting all extremities, intercostal muscles
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5
Q
  • The primary feature of MG is increasing weakness w/sustained muscle contraction
  • Muscle weakness is greatest > exertion or @ the end of the day
  • Purely a motor disorder w/no effect on sensation or coordination
A
  • Reflexes normal
  • Poor posture
  • Bland expression
  • Dysphonia
  • Resp compromise
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6
Q

___ ___ are the 1st to appear in about 16% of MG pts, & refer to symptomatology involving CN’s IX, X, XI, & XII that emerge from the medulla of the brainstem

A

Bulbar symptoms

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7
Q
  • Weakness of the facial muscles produces an expressionless face w/droopy eyelids, smoothed features, & a tendency for the mouth to hang open; smile → snarl d/t weakness
  • Dysphagia & a nasal quality to speech
A
  • Laryngeal involvement produces dysphonia (voice impairment) & inc the pt’s risk for choking & aspiration
  • In severe cases, resp muscle weakness may occur, which may necessitate intubation & mechanical ventilation. Generalized weakness of intercostal muscles results in dec vital capacity & subseq resp failure
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8
Q
  • MG course varies w/remissions & exacerbations; clinical manifestations may progress slowly or quickly & fluctuate day to day; dz severity varies greatly
A
  • Bulbar weakness - muscles of the jaw, face, palate, pharynx, larynx, & tongue - facial nerve, vagus, & hypoglossal nerves
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9
Q

Exacerbations: Precipitating Factors

Rapid Development
▻ Infection
▻ Pregnancy
▻ Anesthesia

A

Temporary Increases
▻ Vaccination
▻ Menstruation
▻ Temp extremes

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10
Q

Management

  • Dx of MG is based upon clinical assessment as well as analysis of diagnostic tests
  • Serological tests, EMG, & the edrophonium test (Tensilon test) aid in establishing a dx
A
  • An assay for AChR antibodies is essential for making a dx of MG
  • The AChR-binding antibodies are found in roughly 80% of pts w/generalized MG but only 55% of pts w/ocular MG
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11
Q

?

Is a diagnostic tool used to evaluate neuromuscular transmission & measures muscle action potential >repeated nerve stimulations

A

Repetitive nerve stimulation

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12
Q

EMG

  • A decrementing response to repeated stimulation is indicative of muscle fatigue

Decrementing = a reduction in the response of the nervous system to repeated stimulation

A
  • A chest CT scan is routinely performed to eval the pt w/MG for thymoma; is more sensitive than plain x-rays
    > Surgical approach to MG management is thymectomy
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13
Q

?

Is a medication that is a reversible inhibitor of AChE

Improves neuromuscular transmission by inc ACh stimulation of the AChRs that are avail

A

Pyridostigmine

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14
Q

?

Is a shorter-acting AChE inhibitor

A

Neostigmine

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15
Q

Immunosuppressant rx’s to treat MG -

prednisone
Imuran (azathioprine)
Cellcept (mycophenolate mofetil)
Cytoxin (cyclophosphamide)

A

Addl therapies

▻ IVIG
▻ Plasmapheresis

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16
Q

Edrophonium aka Tensilon Test

Positive

▻ Inc in muscle strength; improvement in facial weakness & ptosis

A

Negative

! No changes observed >incremental doses
! NOTE - that >incremental doses
Increases in ACh cause buildup in parasympathetic ANS as well

Result - bronchospasm, bradycardia, & diarrhea r/t inc in muscarinic receptors

ATROPINE - muscarinic BLOCKER & therefore the antidote

17
Q
  • Edrophonium or Tensilon is a short-acting, but very RAPID-acting IV anticholinesterase med
  • Temporarily improves neuromuscular transmission by inhibiting AChE [acetylcholine enzyme]; will lead to inc muscle strength in pts w/MG
A
  • Acetylcholine inhibitor Tensilon (edrophonium chloride) given in small doses IV
  • Inhibitor stops the breakdown of acetylcholine thereby inc avail @ the neuromuscular junction
  • Facial weakness, ptosis, is resolved for about 5 min - then test is (+) for MG
18
Q
  • Is also used to test for undermedication (cholinergic crisis 2° to overdose of anticholinesterase drug)
A
  • Clinical manifestations are facial muscle fasciculations, sweating, excessive salivation, & constricted pupils
  • In this case, the Tensilon doesn’t improve muscle weakness but actually inc the weakness
19
Q

?

Is on hand to counteract when used diagnostically

s/e’s - bradycardia, sweating, cramping

A

Atropine

20
Q

! When this test is being conducted, is essential that IV atropine sulfate be present

! IV atropine sulfate is the antidote; it counteracts any severe cholinergic reactions (cardiac dysrhythmias or abd cramping)

A
21
Q

Acetylcholinesterase inhibitor test

  • A short-acting anticholinesterase like edrophonium chloride (Tensilon) or neostigmine methylsulfate (Prostigmin) is given via IV to the pt
  • These rx’s inhibit cholinesterase (an enzyme that breaks down ACh in the neuromuscular junction)
  • This allows for more ACh to bind to the remaining ACh receptors
A
  • Pt is assessed for improvement in muscular strength & also given an IV infusion of a placebo & assessed
  • Improvement in muscle strength w/the med is a strong indicator that pt has MG
22
Q
  • If edrophonium chloride (Tensilon) is used the effects of the med wear off within 3-5 min of the inj
  • Neostigmine methylsulfate (Prostigmin) has a longer duration 1-2 hrs which allows for a better analysis
A
  • Dosing: 2 mg of edrophonium is admin IV as a test dose
    Monitoring HR - bradycardia or v-fib may develop
23
Q
  • Follow-up
    > After observing for about 2 min, if no clear response develops up to 8 addl mg of edrophonium is injected
A
  • A double-blind protocol w/a saline inj as placebo has been advocated
  • Testing should be performed w/pt free of all cholinesterase-inhibitor meds
24
Q

Cholinergic s/e’s of edrophonium

  • May incl inc salivation & lacrimation
  • Mild sweating, flushing, urgency & perioral fasciculations

! Atropine should be readily avail to reverse effects of edrophonium in case of hemodynamic instability

> extra precautions esp important in elderly pts

A

Positive test

  • Most myasthenic muscles respond in 30-45 sec >inj
  • Improvement in strength that may persist for up to 5 min
  • Requires objective improvement in muscle strength
    ! Subjective or minor responses, like reduction of a sense of fatigue, shouldn’t be over-interpreted
25
Q

?

During sustained, forced eyelid closure pt is unable to bury the eyelashes and, after 30 sec, is unable to keep the lids fully closed

A

“Peek” sign

26
Q

Medications/Goals

  1. Provide symptomatic treatment to inc the avail of ACh
  2. Immunosuppression
  3. Alter immunopathogenic mechanisms
  4. Immunomodulatory effect w/thymectomy

2 meds commonly used -
* Mestinon (Pyridostigmine)
* Prostigmine (Neostigmine)

= muscarine stimulation

A

! Important safety note = pts MUST get these meds @ the prescribed times to provide optimal muscle strength

Also important to adhere to med schedule(s) followed @ home

e.g., often taking Pyridostigmine 30-60 min before meals to minimize difficulty w/chewing & swallowing

27
Q

Muscarinic Effects

  • Inc GI motility
  • Inc GI secretion
  • N/V
  • Abd cramping
  • HR slowed
  • BP dec
  • Pupil constriction
A
  • Inc glandular secretions
  • Excessive salivation
  • Sweating, flushing
  • Blurred vision
  • Inc bronchial secretions; bronchospasms

Antidote: Atropine

28
Q

Treatment

▻ Plasmapheresis
- Treatment in exacerbations
- Plasma removed - antibodies believed to cause MG removed & re-infused
- Daily x5

A

▻ IV IgG
- 2nd line treatment for MG; supplies antidote antibodies
1. Given as acute therapy (as a rapidly acting but relatively short-lasting treatment for an autoimmune dz that is itself short-lasting (days to wks) or is currently flaring [e.g., given for GBS]

  1. For chronic autoimmune dz (given approx once every 1-3 mos over time for long-term immunosuppression)

▻ Min s/e’s incl HA, local skin rxn @ infusion site, & flu-like sx’s

29
Q

Treatment

▻ Thymectomy = surgical removal of the thymus gland can produce antigen-specific immunosuppression & result in clinical improvement
> May take up to 3 yrs for pt to benefit from this d/t long life of circulating T cells

A

Diet
▻ Professional eval for chewing and swallowing
▻ May need thickened liquids or even enteral feedings

30
Q

Contraindicated Medication

Anything that blocks muscle activity, such as magnesium, calcium channel blockers, & any meds like antacids & laxatives that contain Mg

⋫ anesthetics
⋫ anti-dysrhythmics - calcium channel blockers, Mg
⋫ some abx
⋫ quinine
⋫ antipsychotics
⋫ barbiturates
⋫ opioids

A

⋫ sedative-hypnotics
⋫ cathartics
⋫ diuretics
⋫ thyroid preparations
⋫ tranquilizers
⋫ Novocain (advise DMD of MG)
⋫ muscle relaxants

31
Q

?

Occurs d/t excessive anticholinesterase medication & is potentially secondary to the pt taking too much of the prescribed MG med

A

Cholinergic crisis

32
Q

?

Is an exacerbation of MG weakness that provokes an acute ep of resp failure that is often c/b a resp infection from viral or bacterial agents

⋫ Inc in weakness
⋫ Inability to clear secretions, swallow, or breathe
! Improves temporarily w/Tensilon

A

Myasthenic crisis

33
Q

Myasthenia Crisis

⋫ Resp, muscles, bulbar weakness

⋫ Myasthenia sx: weakness, incontinence, fatigue

⋫ HTN; inc HR

⋫ Acute treatment strategies; more meds!

A

Cholinergic Crisis

⋫ Muscle twitching to the point of resp weakness
- provide adequate ventilatory support

⋫ Cholinergic sx: hypersecretions, inc resp secretions, n/v, hypermotility (cramping)

⋫ Hypotension

⋫ Improve w/atropine (1 mg IV may be needed)

34
Q

Education

✓ Precipitating factors
✓ Med management
✓ Strategies to conserve energy

A

✓ Measures to minimize risk for aspiration
✓ Emergency care

NUR 202 Week 7 (5 decks)

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