QuestionSBA
QuestionChoice
Although 10-20% of patients with myasthenia graves will have a thymoma, this is not the underlying pathophysiology causing the myasthenia gravis symptoms.
10027027
b
Thymoma
QuestionChoice
This is the pathophysiology of multiple sclerosis. Although this commonly presents in women under the age of 40, it would not account for the fatigue seen on EMG. Multiple sclerosis also classically presents with different symptoms, such as unilateral loss of vision with pain upon eye movement (optic neuritis).
10027029
d
Inflammation causes demyelination and axonal loss
QuestionChoice
This is the pathophysiology of amyotrophic lateral sclerosis, the commonest form of motor neurone disease. Degeneration of the corticospinal tract and alpha motor neurons results in the characteristic mix of upper and lower motor neurone signs seen.
10027030
e
Progressive degeneration of the corticospinal tract and alpha motor neurons
QuestionChoice
This is the pathophysiology of Lambert-Eaton myasthenic syndrome, which is characterised by muscle weakness that improves with exercise. Lower limb weakness, hyporeflexia and an incremental response to repetitive stimulation would be seen.
10027028
c
Autoantibodies against presynaptic voltage-gated calcium channels in the peripheral nervous system
QuestionChoice
The vignette describes the classical presentation of myasthenia gravis (MG). 85% of MG cases are caused by autoantibodies against the nicotinic acetylcholine receptors at the neuromuscular junction. This blockade stops the acetylcholine from triggering muscle contraction. During repeated or sustained muscle contraction, more receptors become blocked, accounting for the muscle weakness seen with increased activity.
10027026
a
Autoantibodies against the nicotinic acetylcholine receptors at the neuromuscular junction
Concept
Chapter
2693
3859
Myasthenia Gravis
Topic
158
Immunology
17803
A 34-year-old woman presents with double vision and eyelid drooping, which is worse at the end of the day. Upon investigation, all of her reflexes are normal, and an EMG shows a diminishing response of muscle fibres with repetitive electrical stimulation.

What is the most likely pathophysiology underlying this condition?
a