S3_L1: Myasthenia Gravis Flashcards
Who wrote the first written description of myasthenia gravis about a woman who temporarily lost her power of speech and became mute as a fish?
Thomas Willis
What is the most common primary disorder of neuromuscular transmission that is chronic and autoimmune in nature?
Myasthenia gravis
What is the usual cause of myasthenia gravis?
acquired immunological abnormality
What does the Latin & Greek term “Myasthenia Gravis” mean?
grave muscle weakness
The hallmark of Myasthenia Gravis is muscle weakness that increases during (1)___ & improves after (2)___.
- periods of activity
- periods of rest
What is the most notorious drug known to adversely affect MG or trigger the recurrence of MG?
Antibiotics
What is the important immunological organ related to myasthenia gravis?
Thymus gland
Which cells found in the thymus express the AChR antigen?
Myoid cells
What is the age of onset of MG for males and females?
Male: middle aged (60-69)
Female: younger aged (20-30)
TRUE OR FALSE: MG is equally present in men and women older than the age of 40 years; however, it is three times more common in women than men under 40 years of age.
True
Source: Merritt
Which stage of MG classification by Osserman is described as mild generalized, slow progression, no crises, drug responsive?
2A
Which stage of MG classification by Osserman is described as acute fulminating, rapid progression with respiratory crises, poor response, some are with thymoma; Hook to mechanical tube and ventilated?
3
Which stage of MG classification by Osserman is described as late severe, severe myasthenia, progression of symptoms over 2 years from class 1 to 2?
4
Which stage of MG classification by Osserman is described as moderately severe, generalized severe skeletal and bulbar involvement, no crises, drug response is less satisfactory?
2B
Which stage of MG classification by Osserman is described as ocular myasthenia?
1
Which stage of MG classification by Osserman is described as MG with poor response to medication as well as muscle atrophy?
5
What is the most sensitive clinical test of neuromuscular transmission and shows increased jitter?
Single Fiber EMG
It is found to be greatest in weak muscles but may be abnormal even in muscles with normal strength
Jitter
TRUE OR FALSE: Patients with mild or purely ocular muscle weakness may have increased jitter only in facial muscles
True
In acquired myasthenia gravis, the ___ muscle membrane is distorted and simplified, having lost its normal folded shape.
Postsynaptic
It is the gold standard and mainstay of treatment for MG
Cholinesterase Inhibitors (pyridostigmine-Mestinon)
The most dramatic response to MG will be from taking what medication?
Pyridostigmine-Mestinon
TRUE OR FALSE: In MG, muscles that control eye and eyelid movement, facial expression, chewing, talking, and swallowing are more affected than muscles that control breathing and neck and limb movements.
True
It is the most commonly used diagnostic procedure for MG
Electromyography (Repetitive Nerve Stimulation)
In RNS and RNSS, the decrementing response of > or ≥ 10% from the initial value is usually seen in the ___ muscles
Proximal
SFEMG is indicated and helpful in pts c ____ RNS
Normal
In generalized MG, the RNS is (1)___, while in ocular MG, the RNS is (2)___.
- sensitive
- not as sensitive (depends on muscle tested)
It is a diagnostic test that determines the amount of antibodies against AChR
Antibodies Against Acetylcholine Receptor Test
3 types of cells present in the thymus that are necessary for the pathogenesis of MG
- Myoid cells
- Antigen presenting cells
- Immunocompetent T-cells
What is affected in MG
Neuromuscular junction
The presence of antibodies reaching the receptors before the released ACh do is an event termed as?
Competitive Inhibition
What are the most common initial symptoms in MG patients?
Ocular motor disturbances (ptosis or diplopia)
TRUE OR FALSE: Bilateral ptosis is a very common manifestation in patients with MG
True
This type of thymectomy approach assures a more complete removal of thymic tissue.
Transsternal
Match the cardinal features of MG with its description/details
- Extraocular muscle weakness
- Nasal speech, LMN
- It is often asymmetric
- Dyspnea, hypoxia (a late finding)
- Affects proximal arms or legs. Affects neck flexors more than extensors
A. Dysarthria
B. Fluctuating weakness
C. Diplopia
D. Ptosis
E. Respiratory insufficiency
- C
- A
- D
- E
- B
What are the two types of cells that interact with each other to produce antibodies within the lymphoid tissue of the thymus?
B-cells and helper T-cells
TRUE OR FALSE: Patients with thymoma usually have more severe disease, higher levels of AChR antibodies, and more severe EMG abnormalities than patients without thymoma
True
TRUE OR FALSE: A pattern is seen in patients whose sx began when they were young (30-60 y/o), a thymoma is detected; however, it is not detected in those whose sx began after age 60
True
Determine whether plasma exchange or IVIG is described
- Used as a short-term treatment for pts c acute/sudden worsening myasthenia
- Pts have a favorable response to high-dose: 2g/kg infused over 2-5 days
- A chronic intermittent treatment for pts who are refractory to all other treatments
- Mechanisms of action: Down-regulation of antibodies directed against AChR and introduction of anti-idiotypic antibodies
- Used to rapidly improve strength before surgery
A. Plasma exchange
B. Intravenous Immune Globulin (IVIG)
C. Both
- C
- B
- A
- B
- A
When during the day does the severity of weakness worsen?
As the day progresses after prolonged use of affected muscles
What stage is described as weakness often becomes fixed and the most severely involved muscles are frequently atrophic after 15-20 years?
Burnt-out stage
Differentiate Bell’s Palsy from Myasthenia gravis
Bell’s palsy - nerve problem
MG - neuromuscular junction problem
Determine which immunosuppressant drug is described
- It is reserved for refractory cases d/t toxicity
- Main adverse effect of the drug is diarrhea
- Acts as a calcineurin inhibitor and reduces the function of effector T cells
- Not as popular due to renal toxicity
- Useful adjunct to steroids in patients who cannot tolerate or fail to respond to prednisone. Most studied immunosuppressant
A. Azathioprine
B. Cyclosporine
C. Cyclophosphamide
D. Mycophenolate
E. Methotrexate
- C
- D
- B
- B
- A
Immunosuppressive drugs are also known as?
Steroid-sparing agents
Source: Merritt
Enumerate the 7 factors that worsen MG Sx
- Emotional upset
- Systemic illness
- Hypothyroidism or hyperthyroidism
- Pregnancy
- Menstrual cycle
- Drugs affecting neuromuscular transmission
- Increase in body temperature
What is the corticosteroid that patients with thymoma have an excellent response to before or after the removal of their tumor?
Prednisone
The maximal favorable response after a thymectomy generally occurs how long after the surgery?
2-5 years
TRUE OR FALSE: Patients with thymomas do not respond as well to thymectomy as do patients without thymoma
True
TRUE OR FALSE: Hyperplastic changes in the thymus indicate an ongoing active immune response
True
TRUE OR FALSE: In MG, ACh is released normally, but its effect on the postsynaptic membrane is reduced and the probability that any nerve impulse will cause a muscle action potential is reduced
True
TRUE OR FALSE: In the era before corticosteroids were used for treatment, approximately one-third of patients c MG improved spontaneously, one-third become worse, and one-third died of the disease. This is the same epidemiologic presentation with stroke
True
What stage is described where symptoms fluctuate over a relatively short period of time and then become progressively severe for several years?
Active stage
What stage is described where fluctuations in strength still occurred but are attributable to fatigue, intercurrent illness, or other identifiable factors?
Inactive stage
TRUE OR FALSE: In 2/3 of patients, maximum weakness occurs during the first year
True
