DISORDERS OF THE NEUROMUSCULAR JUNCTION Flashcards
What is the underlying pathology of in myasthenia gravis?
Antibodies directed against the postsynaptic acetylcholine receptor, which results in a reduction in overall stimulation by acetylcholine on the postsynaptic membrane.
Which muscles groups are most commonly affected by myasthenia gravis?
Proximal limb muscles
Ocular muscles
Bulbar muscles
An abnormality in which organ is often associated with myasthenia gravis?
Thymus - thymus hyperplasia is found in 70% of myasthenia gravis patients below the age of 40
What are the two distinct groups of patients who develop myasthenia gravis (in terms of demographic)?
Young women (20-35) Older men (60-75)
What are the feature of myasthenia gravis associated with young women as opposed to myasthenia gravis associated with older men?
Acute, severely fluctuating, more generalised condition, with increased association HLA-B8 and HLA-DR3.
What are the features of myasthenia gravis associated with older men as opposed to myasthenia gravis associated with young women?
Oculobulbar presentation
What are the ocular symptoms of myasthenia gravis?
Ptosis
Diplopia
What are the symptoms of myasthenia gravis with cranial nerve involvement?
Ptosis Diplopia Weak face and jaw Dysarthria - speech problems Dysphonia - impairment of voice Dysphagia - swallowing
What are the muscle groups of the limbs affected by myasthenia gravis?
Usually proximal - hips and shoulders
Neck flexion and extension - difficulty lifting their head
What are the symptoms associated with myasthenia gravis?
Ptosis Diplopia Weak face and jow Dyarthria Dysphonia Dysphagia Proximal muscle weakness Shortness of breath
What is the key feature of the all of the muscle weakness associated with myasthenia gravis?
Fatiguability
How can fatiguability be demonstrated in someone with myasthenia gravis?
Get a patient to keep their head still and look downward for a period. Then instruct them look up at an object. The eye lids will twitch on the way up.
What happens to the reflexes in someone with myasthenia gravis?
Normal at first but will then fatigue on repeated testing.
What are the signs of myasthenia gravis seen during a neurological examination?
Reduced power with fatiguability
Reduced reflexes with fatiguability
Some degree of muscle wasting (later disease)
Sensory normal
What investigations might you do for someone that presents with the signs and symptoms of myasthenia gravis?
Ice test
Edrophonium test
Look for serum acetylcholine receptor antibody
Look for anti-MUSK (muscle specific kinase) antibodies
Electromyography
Thymus imaging
Look for other autoantibodies