Neuromuscular Flashcards
Of the trunk muscles which are the most frequently involved in MG?
Erector spinae
T or F: The proximal muscles are more vulnerable to weakness in MG similar to myopathies?
T
What antibody involved in MG causes atrophied tongue?
Anti-MuSK
What is the MG Foundation class of the ff:
- Intubated
- With NGT
- Ocular weakness only
- Moderate weakness of limb and axial muscles
- Severe weakness of oropharyngeal muscles
- Class 5
- Class 4b
- Class 1
- Class 3a
- Class 4b
How many percent of isolated ocular myasthenia generalize after being isolated to the eyes for 2 or more years?
15%
In patients with MG what percentage will have
- Non neoplastic lymphofollicular hyperplasia
- Thymic tumors
What are the types of tumors in the thymus?
- 65%
- 10-15%
- Histiocytic cells like the reticulum cells in the center of the follicles
- Lymphocytic– lymphosarcomatous
What are the ultrastructural changes in the neuromuscular junction in MG?
- Reduction and simplification of the post synaptic membrane
- Widening of the synaptic cleft
What percentage of patients with thyrotoxicosis with periodic paralysis also have MG?
T or F: All thymic tumor patients eventually developed MG, sometimes even 15-20 years post resection
5%
T
What percentage of MG patients will have antibodies to AChR protein?
- Generalized MG
- Ocular MG
- 85
2. 60
What is the most sensitive test for detecting a defect in neuromuscular transmission?
Single fiber EMG
How long should one wait for improvement in a postiive
- Edrophonium test
- Neuostigmine test
- 45s then increase dose
2. 10-15 mins
What percentage of diagnosis is confirmed when antibody test, edrophonium test and single muscle fiber test are all done?
95%
How to distinguish polymyositis and IBM from MG?
the absence of EOM involvement
How to distinguish botullism from MG?
Botulism has large unreactive pupils and the eye signs are followed in rapid succession by invovlement of bulbar, trunk and limb muscles
What is the “maximum” dose of Mestinon?
120mg Q3
What is the range of prednisone doses for MG?
15-60mg per day. May even do alternate day doses
What is the prodrug of azathioprine and the enzyme that is responsible for metabolizing it?
Mercaptopurine and thiopurine methyltransferase
What are the 2 drugs for MG backed up by large trials?
Azathioprine and cyclosporine
What is the dose for PLEX for MG?
125ml per kg
What is the dose of IVIG for MG?
2g per kg over 3-5 days
When should thymectomy not be done?
Ocular MG and those not yet at puberty
What anesthetic agents must be avoided in MG?
Neuromuscular blocking agents
T or F. Magnesium should not be used in eclamptic pregnant mothers
T
MG or LE? or both?
- First symptoms are attributable to trunk and girdle muscle weakness
- Increase in strength with first few contractions
- Single fiber with increaesd jitter
- Loss of voltage gated Ca channels in the presynaptic motor nerve terminal
- Treatment with IVIG, prednisone, azathioprine
- LE
- LE
- Both
- LE
- Both
How many percent of LEMS patients have small cell lung CA? How many have cancer?
60
2/3
What is the first line treatment for LEMS?
3,4-diaminopyridine
How long does neonatal myasthenia take to recover?
2 months at the most
Besides neonatal myasthenia complication can result in babies in mothers with MG?
Arthrogryposis
What common antibiotics cause MG exacerbation?
Gentamicin
Fluoroquinolones: Ciprofloxacin
What percentage of MG cases have eventual involvement of the levator palpebrae or extraoculat muscles?
90%
What trunk muscle is most often affected by MG?
Erector spinae
In the MG Foundation grading scale what is the grade for patients with:
- Ocular weakness only
- Use of NGT
- Intubation with mechanical ventilation except when employed for post operative management
- Intubation without mechanical ventilation except when employed for post operative management
- Moderate weakness affecting other than ocular muscles predominantly oropharyngeal muscles
What makes the classifications either a or b?
- Ocular weakness only: Class 1
- Use of NGT: 4b
- Intubation with mechanical ventilation except when employed for post operative management: 5
- Intubation without mechanical ventilation except when employed for post operative management: 5
- Moderate weakness affecting other than ocular muscles predominantly oropharyngeal muscles: 3b
What makes the classifications either a or b?
a predominantly affects limbs, axial muscles or both
b predominantly affects oropharyngeal muscles , respiratory muscles or both
What HLA are associated with MG?
A3 B7 DRW2
Enumerate the 3 mechanisms by which neuromuscular transmission is impaired by MG:
- Ab blocking the binding of ACh to AChR
- Serum IgG from MG patients has been shown to induce an increase in the degradation rate of AChR
- Antibodies cause complement mediated destruction of the post synaptic folds
What findings in single fiber electromyography in consistent with MG?
NB: The variation in the time interval between the two action potentials of the same motor unit is called as “jitter”. SFEMG measures the variation of this inter potential interval (jitter). Jitter is the measurement of variation of the inter-potential interval. This is calculated between the triggered potential and the time-locked, second single muscle fiber action potential.
- Inconstancy of the normally invariant interval between the firing of muscle fibers
- Complete blocking of successive discharges from single muscle fibers belonging to the same motor unit
When neuromuscular transmission is sufficiently impaired, nerve impulses fail to elicit an action potential and this is called ‘blocking’.
The study is considered abnormal if one of the following criteria is met,
Mean jitter value exceeds the upper limit of the normal value
More than 10% of the pairs have increased jitter (two out of twenty pairs)
How to do the neostigmine test?
Neostigmine 1.5mg is given IM– prepare 1.5mg of atropine as rescue
Improvement should occur in 10-15 mins – peak at 20 min and last up to 1h; improvement will last for 60 min
OR 1mg of edrophonium– improvement in 45s. Keep giving 1mg until 10mg if no improvement. Improvement will last for 5 min
What is the maximal useful dosage of pyridostigmine according to Drachman?
120mg every 3 hours
What is the starting dose and the maximum daily dose for prednisone in MG?
How about for azathioprine
15-20mg
50-60mg
50mg BID (100mg daily) Max is 250mg daily
What is the dose for cyclophosphamide for MG
50mg per kg per day for 4 consecutive days
What is the standard dose of IVIG for MG? for GBS?
2g per kg over 3-5 days
400mg (0.4g) per kg IV daily for 5 days
What is the remission prate post thymectomy if the procedure is done int he first year or two after onset of the disease?
35%
50% will improve to some extent
What is the pattern of weakness in Lambert Eaton syndrome?
What is the pathophysiology?
Trunk and girdle muscles are affected are the ones that become weak and fatigable. They will also have a dry mouth, with aching muscles and diminished reflexes
Presynaptic: Autoimmune reduction in calcium mediated quantal release– 2/3 will ahve cancer
Besides MG, what is another example of a post synaptic pathology resulting in weakness?
Snake venom toxins
Lyse muscle, binds Na channels and K channels
Give all the diseases affecting the NMJ:
- Presynaptic
- Synaptic
- Post synaptic
- Botulism, Lambert eaton
- Insecticides/ organophosphates inihibit ACHe
- MG, Snake venom
Approximately 60% of lambert eaton cases have?
Small cell lung cancer
What is the single fiber findings in LEMS?
INCREASE in jitter as well
What is the treatment for LEMS
3,4-diaminopyridine an agent that blocks K channels int he distal motor terminal thus prolonging depolarizations and enhancing ACh vesicle release
Re: Hereditary Myasthenic syndromes:
What are the components of the escobar syndrome?
Arthrogryposis
Pterygia
Respiratory distress
Re: Hereditary Myasthenic syndromes:
How does the fast channel syndrome differ from the slow channel syndrome in terms of treatment?
Avoid 3,4,DAP in slow channel
use it for fast channel
Re: Hereditary Myasthenic syndromes:
What congenital myasthenic syndrome will also have epidermolysis bullosa?
Plectin deficiency
Re: Hereditary Myasthenic syndromes:
What is rapysn?
Plays a role in maintaining the integrity of the post synaptic membrane
Defect in gene causes congenital mysathenia– post synaptic
Re: Hereditary Myasthenic syndromes:
Which congenital myasthenic syndrome presents with limb girdle weakness and has pathology in the synaptic cleft itself?
DOK-7 synopathy
What antibiotics cannot be given to MG patients?
Aminoglycosides
Quinolones
Tetracyclines
