Myasthenia Gravis and Related Disorders Flashcards
T/F
Diplopia is common in MG but it does not correspond to the innervatory pattern of nerve
true
it is the result of asymmetrical weakness of several muscles in both eyes
Cogan’s signs
lid-twitch
twitching of the upper eyelid that appears a moment after the patient moves the eyes from a downward to the primary position
T/F
Bright sunlight aggravates the ocular signs and cold has been said to improve them
true
In MG, muscles of facial expressions, mastication, swallowing, speech, are affected in ____ of patients
80%
In MG, which muscles of the trunk are mostly affected
erector spinae
T/F
In advanced cases of MG, the sphincters of the bladder and bowel may be affected
True
T/F
In MG, smooth and cardiac muscles are involved
False
In MG, the tongue may atrophy as seen in which type of MG patients
those with MuSK
muscle-specific tyrosine kinase
How many percent of MG are seen in children younger than 10
10%
MG
peak age of first symptoms in women? men?
women 20-30
men 50-60
Clinical Grading of MG wherein use of feeding tube is indicated but without intubation
Class IVb
Periods of danger in MG (2)
- danger of death from generalized MG is greatest in 1st year after onset of disease
- 2nd danger in progressive case is 4-7 years after onset
T/F
An increasing duration of purely ocular myasthenia is associated with a decreasing risk of late generalization of weakness
True
T/F
A later age at onset was also associated with a higher incidence of fatal respiratory distress. In general, a patient whose disease begins at a younger age run a more benign course.
True
Localized ocular myasthenia present for a month was associated with a ___% likelihood of generalization
ocular myasthenia restricted for 1 year was associated with _____% to generalize
60%
16%
T/F
Progression of symptoms is more rapid in male than in female patients.
True
How many percent of MG patients attained maximun severity in 1 year? 3 years?
1 yr 67%
3 yrs 83%
How many % of MG patients have
nonneoplastic lymphofollicular hyperpalasia of the thymic medulla?
thymic tumors?
65%
10-15%
Cells found in the centers of follicles in hyperplasia of thymus
helper T lymphocytes
B lymphocytes
plasma cells
2 forms of thymic tumors
- composed of histiocytic cells like the reticulum cells in the center of the follicles
- lymphocytic and considered lymphosarcomatous
T/F
Myasthenia may develop after thymic tumors have been removed, even after 15-20 yrs.
True
In MG, the main ultrastructural alterations occur in the
motor endplate
describe changes in the motor endplate of MG
reduction and simplification in the surface area of the postsynaptic membrane (sparse, shallow, abnormally wide, or absent, secondary synaptic clefts)
widening of synaptic cleft
True or False
The number and size of the presynaptic vesicles and their quanta of acetylcholine ACh are normal.
True
Reason why the ocular and cranial muscles are usually the first to be affected in MG
these muscles are the most continuously active and have the fewest AChRs per motor unit
How many percent of Patients with MG have AChR antibodies
generalized
ocular
generalized - 85%
ocular - 60%
Neuromuscular transmission is impaired in MG in 3 ways
- the antibodies block the binding of ACh to the AChR
- serum IgG from myasthenic patients has been shown to induce an increase in the degradation of AChR
- antibodies cause a complement-mediated destruction of the postsynaptic folds
RNS in MG
rapid reduction in the amplitude of CMAPs during a series of repetitive nerve stimulation of a peripheral nerve at a rate of 3 Hz
reversal of response by neostigmine or edrophonium
Muscarinic effects of Neostigmine
salivation sweating bronchorhea borborygmi bowel cramps diarrhea
after how many minutes of injection with neostigmine can we detect improvement
objective improvement occurs after 10-15 mins
reaches peak at 20 mins
lasts up to 1 hr
dosing of pyridostigmine and neostigmine
30-90 mg given every 6 hrs; rarely exceeds 120mg every 3h
neostigmine 7.5-45mg given every 2-6 hrs
remission rate after thymectomy in MG
35% if done in the first 2 years of disease onset
to 50% will improve to some extent
Plasma exchange
several exchanges 2 to 3.5 L each (125mL/kg) performed over a week
IV Ig
2g/kg in divided doses over 3 to 5 days
how many weeks before deciding to do a tracheostomy
2-3 weeks
Physiologic mechanism in Lambert-Eaton myasthenic syndrome
loss of voltage-gated calcium channels on the presynaptic motor nerve terminal
calcium channels become cross-linked and aggregated by functioning channels
These antibodies against a specific component of the presynaptic membrane have the effect of reducing the presynaptic release of ACh
transitory phenomenon apparent at birth and has a mean duration of about 2-5 weeks; recovery is usually complete within 2 months of birth without later relapse
seen in 10-20 percent of babies born to mothers with myasthenia
Neonatal Myasthenia Gravis
defects in congenital myasthenic syndromes
presynaptic
synaptic
postsynaptic (3/4 of cases)
drugs which can cause myasthenic weakness
neomycin, kanamycin, colistin, streptomycin, polymyxin B, some tetracyclines
ciprofloxacin affects pre and postsynaptic activity
MOA of botolinum toxin
binds to cholinergic motor endings, blocking quantal release of ACh
MOA black widow spider venom
massive release of ACh resulting in muscular contraction and paralysis
MOA d-tubocurarine
binds to AChR
MOA suxamethonium and decamethonium
bind to AChR
MOA organophosphates
binds irreversibly to AChE
MOA malathion and parathion
inhibit AChE
Presynaptic Congenital Myasthenic Syndrome
Episodic apnea
Paucity of synaptic vesicles
reduced quantal release of acetylcholine
Synaptic Congenital Myasthenic Syndrome
AChE Deficiency
DOK-7 synopathy
Postsynaptic Congenital Myasthenic Syndrome
Slow Channel Syndrome Fast Channel Syndrome Primary AChR Deficiency Rapsyn Deficiency Plectin Deficiency Escobar Syndrome
