Neuromuscular disorders Flashcards
What is myasthenia gravis?
Myasthenia gravis is an autoimmune condition affecting the neuromuscular junction.
It causes muscle weakness that progressively worsens with activity and improves with rest.
Who is commonly affected by myasthenia gravis?
Myasthenia gravis affects men and women at different ages, typically affecting women under 40 and men over 60.
Tumours of the _______ gland are associated strongly with myasthenia gravis?
Thymus
Strong link with thymomas (thymus gland tumours).
10-20% of patients with myasthenia gravis have a thymoma.
30% of patients with a thymoma develop myasthenia gravis.
Where is mostly affected in myasthenia gravis?
Affect the proximal muscles of the limbs and small muscles of the head and neck
What symptoms are associated with myasthenia gravis?
Difficulty climbing stairs, standing from a seat or raising their hands above their head
Extraocular muscle weakness, causing double vision (diplopia)
Eyelid weakness, causing drooping of the eyelids (ptosis)
Weakness in facial movements
Difficulty with swallowing
Fatigue in the jaw when chewing
Slurred speech
Treatment of myasthenia gravis?
Pyridostigmine is a cholinesterase inhibitor that prolongs the action of acetylcholine and improves symptoms
Immunosuppression (e.g., prednisolone or azathioprine) suppresses the production of antibodies
Thymectomy can improve symptoms, even in patients without a thymoma
Rituximab (a monoclonal antibody against B cells) is considered where other treatments fail
What is lambert-eaton myasthenic syndrome (LEMS)?
Lambert-Eaton myasthenic syndrome is an autoimmune condition affecting the neuromuscular junction, similar to myasthenia gravis.
However, symptoms for LEMS tend to be more insidious and less pronounced than myasthenia gravis.
In most cases, LEMS is a paraneoplastic syndrome occurring alongside small-cell lung cancer (SCLC). It can occur as a primary autoimmune disorder without the presence of SCLC. True/false?
True
Paraneoplastic syndrome = a group of rare disorders that occur when the immune system has a reaction to a cancerous tumour known as a “neoplasm.”
Pathophysiology of LEMS?
Lambert-Eaton myasthenic syndrome results from antibodies against voltage-gated calcium channels.
These antibodies may be produced in response to small-cell lung cancer (SCLC) cells that express voltage-gated calcium channels.
Key presenting features of LEMS?
Proximal muscle weakness, causing difficulty climbing stairs, standing from a seat or raising the arms overhead
Autonomic dysfunction, causing dry mouth, blurred vision, impotence and dizziness
Reduced or absent tendon reflexes
How does LEMS differ from myasthenia gravis?
Signs and symptoms improve after periods of muscle contraction, which is the reverse of what is seen in myasthenia gravis.
Reflexes may be absent in a rested patient but be present when testing immediately after the patient maximally contracts the associated muscles.
Equally, muscle strength may improve after use.
LEMS management?
Excluding underlying malignancy (e.g., small-cell lung cancer) is essential.
Amifampridine works by blocking voltage-gated potassium channels in the presynaptic membrane, which in turn prolongs the depolarisation of the cell membrane and assists calcium channels in carrying out their action.
