myasthenia gravis Flashcards
men or woman
more woman
what antibodies against
antibodies against the muscle acetylcholine receptor (AChR)
6% antibodies against the muscle-specific kinase (MuSK) are detected.
muscle specific kianses foudn where
Muscle-specific kinases are proteins found where nerve endings and muscle fibers come together (neuromuscular junctions).
moa of pyridostigmine
Pyridostigmine works by inhibiting the acetylcholinesterase (AChE) enzyme from breaking down the neurotransmitter acetylcholine (ACh), and thereby increases the bioavailability of ACh and enhances the transmission of nerve impulses at neuromuscular junctions. therfore improving muscle strength
what cancer is associated with myasthenia
Thymoma and thymic carcinomas are a type of cancer that affects the thymus, an organ located in between the lungs and is part of the lymphatic and immune systems.
sx of myasthenia
The key feature is muscle fatigability - muscles become progressively weaker during periods of activity and slowly improve after periods of rest:
extraocular muscle weakness: diplopia
proximal muscle weakness: face, neck, limb girdle
ptosis
dysphagia
first diplopia
stroke like dropping and dribbling
then speech
ptosois
problems with repeptiibve motions like chewing and eye blinking
what autoimmune disorders associate dwith myasthenia
autoimmune disorders: pernicious anaemia, autoimmune thyroid disorders, rheumatoid, SLE
why do you measure ck in myasthenia
Cases of myasthenia gravis with inflammatory myopathy usually show elevated creatine kinase (CK) levels. There are few case reports of myasthenia gravis with inflammatory myopathy without elevated CK levels, and clinical features and useful diagnostic methods for these patients are little known.
ix for myasthenia
single fibre electromyography: high sensitivity (92-100%)
CT thorax to exclude thymoma
CK normal
antibodies to acetylcholine receptors
positive in around 85-90% of patients
n the remaining patients, about about 40% are positive for anti-muscle-specific tyrosine kinase antibodies
Tensilon test: IV edrophonium reduces muscle weakness temporarily - not commonly used any more due to the risk of cardiac arrhythmia
mx
long-acting acetylcholinesterase inhibitors
pyridostigmine is first-line
immunosuppression is usually not started at diagnosis, but the majority of patients eventually require it in addition to long-acting acetylcholinesterase inhibitors:
prednisolone initially
azathioprine, cyclosporine, mycophenolate mofetil may also be used
thymectomy
myasthenic crisis
Myasthenic crisis is a complication of myasthenia gravis characterized by worsening of muscle weakness, resulting in respiratory failure that requires intubation and mechanical ventilation.
how to treat a myastehnic crisis
plasmapheresis
intravenous immunoglobulins
are antibodies commonly seen in disease limited to ocular muscles
no
antibodies are less commonly seen in disease limited to the ocular muscles
LE associated with whatcancer
Lambert-Eaton myasthenic syndrome is seen in association with small cell lung cancer and to a lesser extent breast and ovarian cance
lambert eaton contrast to myasthenia
repeated muscle contractions lead to increased muscle strength (in contrast to myasthenia gravis)
Features
repeated muscle contractions lead to increased muscle strength (in contrast to myasthenia gravis)
in reality, this is seen in only 50% of patients and following prolonged muscle use muscle strength will eventually decrease
limb-girdle weakness (affects lower limbs first)
hyporeflexia
autonomic symptoms: dry mouth, impotence, difficulty micturating
ophthalmoplegia and ptosis not commonly a feature (unlike in myasthenia gravis)
what drugs exacerbate myasthenia
The most common exacerbating factor is exertion resulting in fatigability, which is the hallmark feature of myasthenia gravis.. Symptoms become more marked during the day
The following drugs may exacerbate myasthenia:
penicillamine
quinidine, procainamide
beta-blockers
lithium
phenytoin
antibiotics: gentamicin, macrolides, quinolones, tetracyclines
what factors cause fatigue in myasthenia gravis
muscle weakness - due to MG - work harder.
If msucles are weak brain sends signals instructing body to do less , our boyd does less andthis i turn feeds back to brian that it is tired resuting in endless cycle - muscle then decondition and we brethe faster even if the exercises is minimal.
poor sleep pattern - steriods making sleeping pattern sbad
pain
low mood
poor nutrition and hydration
Anti-muscle-specific kinase (MuSK) antibodies is incorrect. Muscle-specific receptor tyrosine kinase antibodies are found in a specific subset of MG cases, known as MuSK-MG. MuSK-MG tends to occur more frequently in females and presents with severe muscle weakness, bulbar symptoms (such as difficulty chewing and swallowing), and a higher prevalence of neck and respiratory muscle involvement. While this option may be considered given the patient’s symptoms, the most common antibodies associated with MG are the anti-AChR antibodies, making it a more likely choice in this case.
A 56-year-old woman with myasthenia gravis is due for an elective abdominal hysterectomy. Which commonly used anaesthetic agent would she most likely be resistant to?
Myasthenia gravis (MG) is caused by autoantibodies to postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction. There are significant implications in the administration of anaesthesia, in particular muscle paralysis.
In this question, eliminating ketorolac and sevoflurane as likely distractors is a useful first step - their mechanisms are unrelated to the pathophysiology of MG.
Neostigmine is used in the treatment of MG, so the patient is unlikely to be resistant to its action.
Rocuronium and suxamethonium are both neuromuscular blocking drugs (NMBDs), however they act in different ways. Rocuronium is a non-depolarising NMBD, acting as an antagonist the post-synaptic receptor and leaving fewer receptors available for acetylcholine. In MG, there are already fewer functional receptors available and therefore patients with MG will be more sensitive to rocuronium and will require a lower dose for paralysis.
Suxamethonium is a depolarising NMBD - it acts by binding to and activating the receptor, at first causing muscle contraction, then paralysis. Again, due to a decreased number of available receptors, MG patients are typically resistant to depolarising NMBDs and may require significantly higher doses.
