Flashcards in Myasthenia gravis Deck (12):
Describe the myasthenia gravis. What does it affect? How?
• Affects neuromuscular transmission
• Autoantibodies target POST-synaptic nicotinic Ach receptors --> no EPP
Clinical symptoms of myasthenia gravis?
• Problems chewing food and sometimes swallowing
• Fluctuating muscle weakness and fatigability
• Opthalmoparesis- difficulty executing eye movements in all directions
Muscle groups affected= extraocular, bulbar, face, neck, limb girdle, trunk
Treatment aim myasthenia gravis?
Treatment aim: to increase the amount of Ach in the synaptic cleft, by blocking its metabolism by acetylcholinesterase
Neurological signs for myasthenia gravis?
• Tendon reflexes intact- Why= synapses do not have time to become fatigued with such brief muscle contraction
Decremental muscle response to repetitive nerve stimulation
Describe the ICE test for myasthenia gravis
Used for ptosis. Apply ice block to affected eyelid and look for a reversal of the ptosis. It is thought to be due to the slowing down of the degradation of acetylcholine (reduced temperature, reduced activity of acetylcholinesterase)
Why would you do an CXR for myasthenia gravis?
Need to rule out a thymoma. --> malignancy of the thymus gland. Also lung cancer --> paraneoplastic effect--> lambert eaton syndrome
How do we distinguish myasthenia gravis from lambert eaton syndrome?
Affects presynaptic terminal.
Auto-antibodies interfere with depolarisation by preventing
Ca2+ channels from opening; Usually due to paraneoplasia (small cell lung cancer) but also autoimmune?
Autonomic involvement like constipation, impotence
Tendon reflexes are reduced
Whereas: Myasthenia gravis= Affects Post synaptic terminal!! Nicotinic receptors. Autoimmune, Somatic motor only, Normal tendon reflexes.
Management of myasthenia gravis?
• Pyridostigmine (anticholinesterase)
• Treat relapses with prednisolone with weekly methotrexate OR azathioprine
May need a thymectomy. Only if age of onset is before 50 and the disease is unresponsive to anti-acetylcholinesterases.
WHAT IS THE KEY CLINICAL FEATURE OF MYASTHENIA GRAVIS?
FATIGUEABLE WEAKNESS. WEAKNESS THAT WORSENS WITH EXERCISE OR REPETITION.
What is the MUSK protein for myasthenia gravis
some patients have autoantibodies against supporting MUSK protein at the NMJ rather than acetocholine receptor
how would you ix myasthenia graves?
-Tensilon test using short acting acetylcholinesterase antagonist
-Blood test for autoantibodies-ACH receptor/MUSK