Myasthenia gravis Flashcards Preview

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Flashcards in Myasthenia gravis Deck (18):
1

What antibodies are associated with myasthenia gravis?

ACh receptor Ab
- 80-90% sensitive
MuSK Ab
- positive in 40% of AChR-negative patients.
- more severe weakness, particularly respiratory and proximal weakness (esp neck extension)
- recognised oculobulbar form, with diplopia, ptosis, dysarthria - not purely ocular
- not associated with thymic disease.
LRP4 Ab
- mild-moderate disease
- not associated with thymic disease.
Anti-striated muscle Ab
- positive in 90% of thymomas
Ryanodine receptor Ab
- positive in 70% of thymomas with MG
- marker for severe disease
Titin Ab (in addition to ACh R Ab)
- thymoma and late-onset MG
Agrin Ab
- poor sensitivity but specific for MG

2

What should be specifically checked for an examination?

Sustained upward gaze - weakness of eyelid elevators and oculomotor muscles
Peek sign - eyelids separate after 30sec of closing, and sclera is visible.
Dysarthria - palate weakness
Dysphonia on counting - bulbar weakness
Smiling causes snarling expression
Neck flexion weakness
Flap 1 arm then test muscle strength together - asymmetrical due to fatigue of one arm

3

What does EMG show?

Repetitive stimulation shows progressive decrease in amplitude of action potentials
Needle examination - motor unit potential variation and, sometimes, fibrillation potentials and myopathic changes
Single-fibre EMG - increased jitter and blocking

4

What other investigations should be performed in MG?

Thymoma search - CXR, chest CT or MRI
Respiratory function tests - weakness in muscles of respiration

5

What is myasthenic crisis and how is it treated?

Crisis involves respiratory weakness causing respiratory failure. Often caused by an infection. Treat with ABx, although aminoglycosides may worsen symptoms.

6

What is first line treatment for Myasthenia Gravis?

Acetylcholinesterase inhibitors - pyridostigmine
K supplements and K-sparing diuretics may improve symptoms but are rarely used

7

What if acetylcholinesterase inhibitors fail?

Steroids - may worsen symptoms and therefore should be monitored closely during initiation.
Immunosuppressants next line - AZA may be used as steroid-sparing agent, however should never be used as monotherapy.
Rituximab in desperate cases

8

What % of myasthenia gravis have isolated ocular signs?

15%

9

Which antibodies are implicated in isolated ocular myasthenia gravis?

ACh and LRP4 (not MuSK)

10

What autoimmune diseases are often associated with myasthenia gravis?

Thyroiditis (most commonly)
SLE and RA
NMO
ALS

11

Kv1.4 Ab in myasthenia gravis are associated with which coexisting cardiac condition?

Myocarditis

12

What is the most effective cholinesterase inhibitor used in myasthenia gravis?
Which subpopulation is it less effective in?

Pyridostigmine
Less effective in MuSK positive patients

13

What is second line Rx for myasthenia gravis?
Third? Fourth?

2nd - Prednisone + AZA
3rd - Mycophenolate (mild) or rituximab (moderate)
4th - MTX, cyclosporin, tacrolimus

14

How is myasthenic crisis treated?

IVIG or plasmapheresis

15

Which myasthenia patients should have a thymectomy?

Recommended in:
- Those with thymomas
- Early-onset myasthenia gravis
- Generalised myasthenia gravis and ACh receptor Abs. 70% of these show improvement after thymectomy.
- Seronegative MG with generalised disease and biomarkers similar to early-onset MG

Not recommended in:
- MuSK or LRP4 Ab positive
- Ocular MG
- Seronegative MG

16

Which medications may precipitate a myasthenic crisis?

Aminoglycosides
Tetracyclines
Fluoroquinolones
Macrolides
Muscle relaxants
Beta blockers
Calcium channel blockers
Botox
Iodine
Penicillamine

17

What is the mechanism of action of fingolimod?

Prevention of lymphocytes from migrating out of lymph nodes

18

What side effects are associated with alemtuzumab?

Autoimmune thyroid disease
Immune thrombotic thrombocytopenia
Renal disease - membranous GN